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MathILy and MathILy-Er Math Jam: Views of the N-Cube

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AoPS Instructor and MathILy Director dr. sarah-marie belcastro leads students in exploration of the N-cube and answers questions about {MathILy, MathILy-Er}.

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Facilitator: sarah-marie belcastro

5space 2019-03-18 19:31:24
In this math jam, AoPS Instructor and MathILy Director dr. sarah-marie belcastro (smbelcas) will lead participants in an exploration of the N-cube from geometric and combinatorial viewpoints. Time will be reserved for a discussion of {MathILy, MathILy-Er} along with any questions you may have about the programs and application process.
5space 2019-03-18 19:31:37
For now, please hold your questions -- we'll let you know when you can start asking questions. Also, due to the number of people attending tonight, we may not be able to get to every question.
5space 2019-03-18 19:31:54
sarah-marie belcastro (smbelcas) earned her Ph.D. in mathematics from the University of Michigan back in 1997 and did her undergraduate work in mathematics and astronomy at Haverford College well before that. She currently directs the summer program MathILy, and has taught a huge variety of mathematics courses---standard and non-standard, undergraduate and graduate in level---to college students and to high-ability high-school students, at institutions including Smith College, Bowdoin College, Sarah Lawrence College, and the Hampshire College Summer Studies in Mathematics. sarah-marie's favorite research is in topological graph theory. Among her many non-pure-mathematics interests are the mathematics of knitting, pharmacokinetics, dance (principally ballet and modern), and changing the world. You may find tons of information (about her, and about other things) at her website http://www.toroidalsnark.net.
smbelcas 2019-03-18 19:32:12
Hi, everybody!
smbelcas 2019-03-18 19:32:18
I see there are some students from my past AoPS classes here .
smbelcas 2019-03-18 19:32:26
Welcome to this combined-topic Math Jam! We are going to do some MAAAAAAAATH, and then I'll tell you a tiny bit about {MathILy, MathILy-Er}, and then I will answer questions about {MathILy, MathILy-Er}.
fibonacci11101 2019-03-18 19:32:35
yay
NoDealsHere 2019-03-18 19:32:35
hey
SwimWithDolphin 2019-03-18 19:32:35
H0i
evankeri 2019-03-18 19:32:35
hi
5space 2019-03-18 19:32:38
Okay, I'll now hand the room off to your discussion leader for today, sarah-marie!
smbelcas 2019-03-18 19:32:45
You might like to have some scratch paper handy.
smbelcas 2019-03-18 19:32:54
Those of you who have had me for class know that after I ask a question, I usually won't say anything until you have collectively responded. So don't be surprised if things look quiet for a few moments---I'm trying to give you a little bit of thinking/typing space.
smbelcas 2019-03-18 19:33:05
Additionally, please explain your reasoning when you respond. And pay some attention to the responses that get passed into the classroom---they are chosen to help everyone's thinking.
smbelcas 2019-03-18 19:33:16
Finally, the math we do this evening is a tiny sample of what is done at {MathILy, MathILy-Er}. We do this same material faster and we take it much further; today we're just scratching the surface. (If you think it's slow/easy at the start, be patient---it will ramp up!) And of course because {MathILy, MathILy-Er} are face-to-face, class is all much louder and laughier and more student-run.
smbelcas 2019-03-18 19:33:29
Let's start with a picture:
smbelcas 2019-03-18 19:33:32
http://aops-docs.s3.amazonaws.com/MathILy/square-seq.jpg
smbelcas 2019-03-18 19:33:39
What do you think comes next in this sequence? (Just the one thing that comes next...)
Redragon 2019-03-18 19:34:10
cube
cad314 2019-03-18 19:34:10
cube
jechi7 2019-03-18 19:34:10
cube
Rishi763 2019-03-18 19:34:10
a cube
EXL 2019-03-18 19:34:10
cube
Mathpluspianoequalslife 2019-03-18 19:34:10
lol I mean just a cube
sansae 2019-03-18 19:34:10
Cube!
Bananaman27 2019-03-18 19:34:10
a cube?
PugLord 2019-03-18 19:34:10
cube
bkim0325 2019-03-18 19:34:10
a cube
Purplegrape 2019-03-18 19:34:10
cube
smbelcas 2019-03-18 19:34:13
Right, it should be a cube.
smbelcas 2019-03-18 19:34:19
http://aops-docs.s3.amazonaws.com/MathILy/cube-seq.jpg
smbelcas 2019-03-18 19:34:23
And what do you think comes after that?
gozomete 2019-03-18 19:35:15
4 dimension cube
evankeri 2019-03-18 19:35:15
4d cube? idk
Rishi763 2019-03-18 19:35:15
a 4-d cube?
bever209 2019-03-18 19:35:15
tesseract
bkim0325 2019-03-18 19:35:15
a 4-dimensional cube thing
sansae 2019-03-18 19:35:15
Four dimensional cube?!
SwimWithDolphin 2019-03-18 19:35:15
tessaract
cad314 2019-03-18 19:35:15
4d "cube"
monkeycalculator 2019-03-18 19:35:15
Tesseract
claserken 2019-03-18 19:35:15
hypercube
haha0201 2019-03-18 19:35:15
tesseract
AwesomeDude86 2019-03-18 19:35:15
tesseract
Damalone 2019-03-18 19:35:15
4 dimensional cube
gozomete 2019-03-18 19:35:15
4d cube comes next
smbelcas 2019-03-18 19:35:18
Now we run into a problem. Who knows what a tesseract or a hypercube mean? These terms aren't defined. Let's back up a little bit.
smbelcas 2019-03-18 19:35:25
We understand at a glance that there is a progression here. What exactly is progressing as we go further in the sequence---what's changing?
Hermain 2019-03-18 19:36:03
the dimension
villagevinegar 2019-03-18 19:36:03
the number of dimensions
bkim0325 2019-03-18 19:36:03
one dimension is added every time
ad46578 2019-03-18 19:36:03
the dimensions?
rubixsolver 2019-03-18 19:36:03
number of dimensions
PugLord 2019-03-18 19:36:03
the dimensions
AwesomeDude86 2019-03-18 19:36:03
the number of dimensions
spoamath321 2019-03-18 19:36:03
dimensions
EXL 2019-03-18 19:36:03
num of dimensions
Mathlete99s 2019-03-18 19:36:07
the dimension it seems
smbelcas 2019-03-18 19:36:10
Indeed, it's the dimension. What are the dimensions of each of those first four objects in the sequence?
MrMXS 2019-03-18 19:36:43
$0,1,2,3$
matharcher 2019-03-18 19:36:43
0,1,2,3
imatrashloser 2019-03-18 19:36:43
0, 1 , 2, 3
avisioner 2019-03-18 19:36:43
0 1 2 3
cad314 2019-03-18 19:36:43
0, 1, 2, 3
monkeycalculator 2019-03-18 19:36:43
0, 1, 2, 3 respectively
StickyWashington 2019-03-18 19:36:43
0, 1, 2, and 3
Damalone 2019-03-18 19:36:43
0,1,2,3
StanDaMan 2019-03-18 19:36:43
0, 1, 2, 3
rubixsolver 2019-03-18 19:36:43
0, 1, 2, 3
AwesomeDude86 2019-03-18 19:36:43
0, 1, 2, and 3
Mathpluspianoequalslife 2019-03-18 19:36:43
0,1,2,3
gozomete 2019-03-18 19:36:43
0, 1, 2, 3, 4...
PugLord 2019-03-18 19:36:43
0d, 1d, 2d, 3d
EXL 2019-03-18 19:36:43
0,1,2,3
smbelcas 2019-03-18 19:36:45
Without getting into the details of the definition of "dimension" (which turns out to need some fairly advanced mathematics to describe precisely), we will agree that a point has $0$ dimensions, so these four objects have dimension $0, 1, 2, 3$.
smbelcas 2019-03-18 19:36:56
Now, what can we say about the next object in the sequence?
ad46578 2019-03-18 19:37:35
4d
bkim0325 2019-03-18 19:37:35
it's 4 dimensions
smartninja2000 2019-03-18 19:37:35
it has 4 dimensions?!
fibonacci11101 2019-03-18 19:37:35
4d
kshah21 2019-03-18 19:37:35
4d
MrMXS 2019-03-18 19:37:35
$4$-dimensional
rubixsolver 2019-03-18 19:37:35
it has four dimensions!
silverpiano 2019-03-18 19:37:35
It would be 4D?
evankeri 2019-03-18 19:37:35
it is 4d, or four-dimensional
sansae 2019-03-18 19:37:35
Its has dimension 4
cad314 2019-03-18 19:37:35
it is 4d
avisioner 2019-03-18 19:37:35
it is 4d
phanithans1 2019-03-18 19:37:35
It will have 4-dimensions
Damalone 2019-03-18 19:37:35
4 dimensions
StickyWashington 2019-03-18 19:37:35
It will apparently have 4 dimensions according to the sequence
villagevinegar 2019-03-18 19:37:35
it should have 4 dimensions and equal length along each dimension
smbelcas 2019-03-18 19:37:37
Right, it should be $4$-dimensional. This sets us up for thinking more deeply:
smbelcas 2019-03-18 19:37:38
How do we form this sequence? That is, how do we go from one object in the sequence to the next one?
smartninja2000 2019-03-18 19:38:32
Increase the number of dimensions by 1
gozomete 2019-03-18 19:38:32
add 1d
MathGenius_ 2019-03-18 19:38:32
add a dimension
kshah21 2019-03-18 19:38:32
We keep on going up and up in dimension
del-math 2019-03-18 19:38:32
How do we add a 4th dimension?
smbelcas 2019-03-18 19:38:34
Somehow we're going up a dimension. But how, precisely, do we do that?
imatrashloser 2019-03-18 19:39:10
here's the thing: points determine lines, lines determine squares, squares determine cubes, cubes determine tesseracts
fishy15 2019-03-18 19:39:10
take 2 copies of the object and connect the corresponding vertices
SwimWithDolphin 2019-03-18 19:39:10
You pull the last one out into a new, orthogonal dimension
monkeycalculator 2019-03-18 19:39:10
Duplicate the object. Connect pairwise corresponding points
cad314 2019-03-18 19:39:10
extending lines from points and planes from lines
villagevinegar 2019-03-18 19:39:10
we add one more copy in the same dimension, then connect the two copies
smbelcas 2019-03-18 19:39:14
These are reasonable general descriptions. Let's look at the process one step at a time. What do we do to go from a point to a line segment?
ad46578 2019-03-18 19:40:10
add a point and draw a line connecting the points
DOGSTREET1 2019-03-18 19:40:10
we draw another point and connect the points
MrMXS 2019-03-18 19:40:10
copy the point then connect the two
villagevinegar 2019-03-18 19:40:10
we add one more point, then connect the two points
Damalone 2019-03-18 19:40:10
we double the number of vertices and connect them with a line
phanithans1 2019-03-18 19:40:10
add another point and connect it
ChickenAgent2227-_- 2019-03-18 19:40:10
sweep it across the next dimension?
bkim0325 2019-03-18 19:40:10
add a point and connect the original and the new one
StickyWashington 2019-03-18 19:40:10
Add a new line at a right angle and duplicate the object along it
smbelcas 2019-03-18 19:40:12
We moosh the point one unit over, and keep the trail it leaves.
smbelcas 2019-03-18 19:40:20
(Points to ChickenAgent for the best answer.)
smbelcas 2019-03-18 19:40:23
http://aops-docs.s3.amazonaws.com/MathILy/p-moosh.jpg
smbelcas 2019-03-18 19:40:29
What do we do to go from a line segment to a square?
mgrimalo 2019-03-18 19:41:18
sweep the whole segment
fishy15 2019-03-18 19:41:18
same process but upwards for the entire line
cad314 2019-03-18 19:41:18
move the line up one unit and keep the trail
Damalone 2019-03-18 19:41:18
sweep the line up through the second dimension
ad46578 2019-03-18 19:41:18
scoot the line segment across to another dimension and keep its trail
ChickenAgent2227-_- 2019-03-18 19:41:18
moosh the line segment over a bit
jumpmonkey 2019-03-18 19:41:18
stratch the line
villagevinegar 2019-03-18 19:41:18
we sweep the line segment over by one unit
smbelcas 2019-03-18 19:41:20
http://aops-docs.s3.amazonaws.com/MathILy/l-moosh.jpg
smbelcas 2019-03-18 19:41:24
We moosh the segment one unit over, and keep the trail it leaves. But wait---what direction do we moosh in? Does it matter?
Mathpluspianoequalslife 2019-03-18 19:42:13
perpendicular
Captain_Crush 2019-03-18 19:42:13
the direction does matter
monkeycalculator 2019-03-18 19:42:13
in any orthogonal direction
StickyWashington 2019-03-18 19:42:13
At a right angle to the other dimension...s...
Allen31415 2019-03-18 19:42:13
it is perpendicular to all other directions.
lcalvert99 2019-03-18 19:42:13
Perpendicular
fishy15 2019-03-18 19:42:13
as long as its a new dimension perpendicular to the line
JCN360 2019-03-18 19:42:13
it is moved perpendicularly to the line segment.
smbelcas 2019-03-18 19:42:15
Yes, it matters a lot. We have to moosh perpendicular to the line segment, or else we'll get a parallelogram instead of a square.
smbelcas 2019-03-18 19:42:32
(Or just a line if we choose really badly.)
smbelcas 2019-03-18 19:42:36
(If you're worried about what moosh really means, it is a type of Cartesian product. Of course, for that to make sense, you have to already know what a Cartesian product is...)
smbelcas 2019-03-18 19:42:48
Okay. What about going from a square to a cube?
Mathpluspianoequalslife 2019-03-18 19:43:42
moosh it perpendicular to the square (upwards)
ad46578 2019-03-18 19:43:42
moosh the square into a perpendicular dimension and keep the trail it leaves
EXL 2019-03-18 19:43:42
moosh perpendicularly
cad314 2019-03-18 19:43:42
extend the square out and keep the trail
MathGenius_ 2019-03-18 19:43:42
push the entire square over forward and keep the trail
villagevinegar 2019-03-18 19:43:42
moosh the square by one unit
StickyWashington 2019-03-18 19:43:42
Moosh the square 'backwards'
ChickenAgent2227-_- 2019-03-18 19:43:42
moosh it along the z-axis
mgrimalo 2019-03-18 19:43:42
sweep the square in a perpendicular manner to get a 3d object
kshah21 2019-03-18 19:43:42
push the square in a direction perpendicular to the square and keep the path
smbelcas 2019-03-18 19:43:44
Right, we moosh the square one unit in a direction perpendicular to the square, and keep the trail it leaves.
smbelcas 2019-03-18 19:43:47
http://aops-docs.s3.amazonaws.com/MathILy/s-moosh.jpg
smbelcas 2019-03-18 19:43:58
And what comes next?
EXL 2019-03-18 19:44:58
moosh again
avisioner 2019-03-18 19:44:58
moosh outwards
ad46578 2019-03-18 19:44:58
moosh the cube one unit perpendicular to the cube and keep the trail it leaves
MrMXS 2019-03-18 19:44:58
move it in another direction perpendicular to those three
cad314 2019-03-18 19:44:58
moosh the cube one unit in a perpendicular direction and keep the trail
Allen31415 2019-03-18 19:44:58
moosh the cube into a direction perpendicular to it?
JCN360 2019-03-18 19:44:58
Just moosh the cube into the fourth dimension (which we cannot picture).
StickyWashington 2019-03-18 19:44:58
...We moosh it at a right angle to a cube 'towards the fourth dimension' 0.O
rubixsolver 2019-03-18 19:44:58
we moosh the cube one unit perpendicular to the cube and keep the trail
StanDaMan 2019-03-18 19:44:58
move it perpendicular again??? Which way even is perpendicular?
smbelcas 2019-03-18 19:45:00
Exactly. We moosh the cube one unit in a direction perpendicular to the cube, and keep the trail it leaves.
smbelcas 2019-03-18 19:45:01
http://aops-docs.s3.amazonaws.com/MathILy/c-moosh.jpg
smbelcas 2019-03-18 19:45:19
We have agreed that the resulting object is $4$-dimensional, and it's certainly cube-like, so let's call it a 4-cube.
smbelcas 2019-03-18 19:45:36
Here are all the cubes we've made so far, for reference:
smbelcas 2019-03-18 19:45:38
http://aops-docs.s3.amazonaws.com/MathILy/four-seq.jpg
smbelcas 2019-03-18 19:46:04
How do we make a $5$-cube? Can you draw one (on paper, not on screen---that would take too long)?
StickyWashington 2019-03-18 19:47:18
You would moosh the 4-cube
mandrake41 2019-03-18 19:47:18
moosh it perpendicular again
Allen31415 2019-03-18 19:47:18
moosh the 4-cube perpendicular to it.
kshah21 2019-03-18 19:47:18
We push it to the right and leave the trail it left behind.
cad314 2019-03-18 19:47:18
moosh the 4-cube in a perpendicular direction and keep the trail
shrungpatel 2019-03-18 19:47:18
We moosh the 4-cube one unit in a direction perpendicular to the 4-cube, and keep the trail it leaves.
ad46578 2019-03-18 19:47:18
moosh the 4-cube one unit perpendicular to the 4-cube and keep the trail it leaves. drawing it is perhaps possible but not pretty
Mathlete99s 2019-03-18 19:47:18
Move the 4 cubes perpendicular with respect to the 5th dimension i think....
smbelcas 2019-03-18 19:47:22
Just as we have done for earlier dimensions, we moosh the $4$-cube one unit in a direction perpendicular to the $4$-cube, and keep the trail it leaves.
smbelcas 2019-03-18 19:47:29
How do we make an $n$-cube?
ChickenAgent2227-_- 2019-03-18 19:48:32
moosh an $n-1$-cube
SwimWithDolphin 2019-03-18 19:48:32
You moosh the $n-1$cube
shrungpatel 2019-03-18 19:48:32
We moosh the (n-1)cube one unit in a direction perpendicular to the (n-1)cube, and keep the trail it leaves.
ad46578 2019-03-18 19:48:32
moosh the (n-1)-cube one unit perpendicular to the (n-1) cube and keep the trail
MrMXS 2019-03-18 19:48:32
take an $(n-1)$-cube and move it in a new perpendicular direction
Rishi763 2019-03-18 19:48:32
we moosh an n-1 cube
evankeri 2019-03-18 19:48:32
mush an n-1 cube into the nth dimension, keep the trail
Allen31415 2019-03-18 19:48:32
moosh an $(n-1)$ cube perpendicular to it.
cad314 2019-03-18 19:48:32
moosh the (n-1)-cube in a perpendicular direction and keep the trail
smbelcas 2019-03-18 19:48:33
Yup. We moosh a $(n-1)$-cube one unit in a direction perpendicular to the $(n-1)$-cube, and keep the trail it leaves.
EXL 2019-03-18 19:48:57
moosh a point n times
gozomete 2019-03-18 19:48:57
moosh it one unit perpendiculary and keep the trail
avisioner 2019-03-18 19:48:57
moosh one unit in a perpendicular direction n times
smbelcas 2019-03-18 19:48:58
Another way to do this is to start with a point and moosh $n$ times.
smbelcas 2019-03-18 19:49:01
Some of you have wondered where these extra perpendicular directions are.
smbelcas 2019-03-18 19:49:08
One answer: Usually when you graph things, you use the $x$ axis and the $y$ axis, and for $3$-dimensional things, the $z$ axis. Here, we also use the $w$ axis, and for the $5$-cube, the $v$ axis.
smbelcas 2019-03-18 19:49:19
The $w$ axis is perpendicular to the $x, y$, and $z$ axes. The $v$ axis is perpendicular to the $x, y, z$, and $w$ axes.
smbelcas 2019-03-18 19:49:27
Just like you can't draw the $z$ axis as perpendicular to the $x$ and $y$ axes on paper, but you can still understand where it goes in $3$ dimensions...
smbelcas 2019-03-18 19:49:43
...you can't place the $w$ axis as perpendicular to the $x, y$, and $z$ axes in regular space, but you can still understand where it goes in $4$ dimensions. There isn't room for the $w$ axis in regular space, but there is enough room in your head. With practice, you can visualize it pretty clearly.
smbelcas 2019-03-18 19:50:10
Anyway: $5$-cube!
smbelcas 2019-03-18 19:50:11
http://aops-docs.s3.amazonaws.com/MathILy/5-cube.jpg
imatrashloser 2019-03-18 19:50:31
my eyes
cad314 2019-03-18 19:50:31
Wow!
SwimWithDolphin 2019-03-18 19:50:31
Holy guacamole
Nami24 2019-03-18 19:50:31
WOW
gozomete 2019-03-18 19:50:31
WHOA!!
avisioner 2019-03-18 19:50:31
what?
mandrake41 2019-03-18 19:50:40
wat
Purplegrape 2019-03-18 19:50:40
coool
smbelcas 2019-03-18 19:50:41
$6$-cube!
smbelcas 2019-03-18 19:50:43
http://aops-docs.s3.amazonaws.com/MathILy/6-cube.jpg
DOGSTREET1 2019-03-18 19:51:05
too many lines!!! brain overload
ChickenAgent2227-_- 2019-03-18 19:51:05
help me please
Mathlete99s 2019-03-18 19:51:05
WOW
Mathlete161 2019-03-18 19:51:05
Holy goly godapppers
PracticingMath 2019-03-18 19:51:05
Ouch my brain
Nami24 2019-03-18 19:51:05
wut is life
MathGenius_ 2019-03-18 19:51:05
omg
kshah21 2019-03-18 19:51:05
(X_X)
avisioner 2019-03-18 19:51:05
cough cough
bkim0325 2019-03-18 19:51:05
wow
Allen31415 2019-03-18 19:51:05
It looks complicated...
ad46578 2019-03-18 19:51:05
my brain hurts
smbelcas 2019-03-18 19:51:07
Okay, that was just for fun. Sometimes I get a bit excited.
karthik_malasani 2019-03-18 19:51:15
Looks great! How did you draw these?
spoamath321 2019-03-18 19:51:15
How did you do it?
avisioner 2019-03-18 19:51:15
wowowowowowow where did you get this
smbelcas 2019-03-18 19:51:25
I drew these diagrams in a technical illustration program.
smbelcas 2019-03-18 19:51:35
(Not in Asymptote.)
smbelcas 2019-03-18 19:51:39
So far we have only constructed the $n$-cube visually. Let us now situate it in space. Again, we'll go dimension by dimension.
smbelcas 2019-03-18 19:51:47
The most convenient place to put a single point (a $0$-cube) is at $0$.
smbelcas 2019-03-18 19:51:52
What should the ends of our $1$-cube line segment be, in terms of coordinates?
villagevinegar 2019-03-18 19:52:43
0 and 1
Allen31415 2019-03-18 19:52:43
$(0), (1)$
ad46578 2019-03-18 19:52:43
wait it could be anywhere 1 unit away from 0! cool!
Damalone 2019-03-18 19:52:52
Or 0 and 1 on the number line
smbelcas 2019-03-18 19:52:54
Yes, we put them at $0$ and at $1$.
smbelcas 2019-03-18 19:53:03
What about the corners of a square (a $2$-cube)?
villagevinegar 2019-03-18 19:53:39
(0,0), (0,1), (1,0), (1,1)
Mathlete99s 2019-03-18 19:53:39
(0,0) (1,0) (0,1) (1,1)
MrMXS 2019-03-18 19:53:39
$(0,0),(1,0),(0,1),(1,1)$
spoamath321 2019-03-18 19:53:39
(0,0)(1,0)(0,1)(1,1)
Allen31415 2019-03-18 19:53:39
$(0,0), (0,1), (1,0), (1,1)$
ChickenAgent2227-_- 2019-03-18 19:53:39
$(0,0);(0,1);(1,0);(1,1)$
cad314 2019-03-18 19:53:39
(0,0) (0,1) (1,1) (1,0)
mandrake41 2019-03-18 19:53:39
(0,0), (1,0), (1,1), (0,1)
karthik_malasani 2019-03-18 19:53:39
(0,0),(0,1),(1,1),(1,0)
SwimWithDolphin 2019-03-18 19:53:39
$(0, 0), (0, 1), (1, 0), (1, 1)$
Damalone 2019-03-18 19:53:39
(0,0),(1,0),(0,1),(1,1)
smbelcas 2019-03-18 19:53:39
For consistency, we place them at $(0,0), (0,1), (1,0)$, and $(1,1)$.
smbelcas 2019-03-18 19:53:47
Now I'm just going to ask you a volley of questions: How many corners does a $3$-cube have? What about a $4$-cube? ...an $n$-cube? What are the coordinates of those corners? Is there an easy way to describe them?
smbelcas 2019-03-18 19:56:28
I'm going to pass your responses through in batches by common theme.
kshah21 2019-03-18 19:57:04
8
da-rong_wae 2019-03-18 19:57:04
2^(n-1)
karthik_malasani 2019-03-18 19:57:04
3 cube 8 corners, 4 cube 16 corners, n cube 2^n corners
motorfinn 2019-03-18 19:57:04
A 3-cube has the vertices of a cube, or 8.
rubixsolver 2019-03-18 19:57:04
8 and 16, powers of 2
evankeri 2019-03-18 19:57:04
8 corners, but the real name is vertices
smbelcas 2019-03-18 19:57:05
A $3$-cube has $8$ corners. A $4$-cube has $16$ corners.
villagevinegar 2019-03-18 19:57:43
8, 16...2^n
SwimWithDolphin 2019-03-18 19:57:43
$2^n$ for number
spoamath321 2019-03-18 19:57:43
2^n
da-rong_wae 2019-03-18 19:57:43
2^n
cad314 2019-03-18 19:57:43
3-cube: 8 verticies 4-cube: 18 verticies n-cube:$2^n$ verticies
motorfinn 2019-03-18 19:57:43
We can model the number of corners by 2^(n) where our figure is an n-cube.
Mathlete99s 2019-03-18 19:57:43
it seems n cube 2^n corners
ad46578 2019-03-18 19:57:43
a 3-cube has 8, a 4-cube has 16, and an n-cube has 2^n corners
mjz6202007 2019-03-18 19:57:43
a n-cube would have 2^n
DOGSTREET1 2019-03-18 19:57:43
an n cube as 2^n corners!
smbelcas 2019-03-18 19:57:45
There are lots of conjectures that an $n$-cube has $2^n$ corners.
jerry_yang 2019-03-18 19:57:55
(0,0,0)(0,0,1)(0,1,0)(1,0,0)(0,1,1)(1,0,1)(1,1,0)(1,1,1)
jumpmonkey 2019-03-18 19:57:55
(0,0,0), (0,0,1), (0,1,1), (0.1.0) , (1,1,0) , (1, 0,0)
avisioner 2019-03-18 19:57:55
ok

3d is 0,0,0;0,0,1;0,1,0;0,1,1;1,0,0;1,0,1;1,1,0 and 1,1,1 in other words binary
kshah21 2019-03-18 19:58:06
oops, (0,0,0) (0,0,1) (0,1,0) (1,0,0) and so on
avisioner 2019-03-18 19:58:13
4d is

0,0,0,0;0,0,0,1;0,0,1,0;0,0,1,1;0,1,0,0;0,1,0,1;0,1,1,0;0,1,1,1;1,0,0,0;1,0,0,1;1,0,1,0;1,0,1,1;1,1,0,0;1,1,0,1;1,1,1,0;1,1,1,1
smbelcas 2019-03-18 19:58:15
A 3-cube has corners at $(0,0,0), (1,0,0), (0,1,0), (0,0,1), (1,1,0), (1,0,1), (0,1,1)$, and $(1,1,1)$.
Allen31415 2019-03-18 19:58:47
There are $2^n$ vertices on an $n-$cube, the vertices are all possible configurations of 0 and 1 as coordinates.
ChickenAgent2227-_- 2019-03-18 19:58:47
a $n$-cube has $2^n$ vertices. They are all in the form $(x,y,z,...)$ where there are $n$ coordinates and each one can be 0 or 1
mandrake41 2019-03-18 19:58:47
an n-cube has 2^n corners, and they go from(0,0,...0(n zeroes)) to (1,1,...1(n ones))
Damalone 2019-03-18 19:58:47
2^n corners. The corners are of the form (a_1,a_2,...a_n) where a_i can be 0 or 1
MrMXS 2019-03-18 19:58:47
yeah basically the $2^{n}$ points represented by $(c_{1},c_{2},\dots c_{n})$ where each $c_{i}=0$ or $1$
villagevinegar 2019-03-18 19:58:47
for an n-cube, there are 2^n corners. Each vertex is described by n numbers -- all zeros and ones: for example for n=6, one of the vertices might be (p1,p2,p3,p4,p5,p6) where p_i=0 or 1
cad314 2019-03-18 19:58:47
n-cube: all coordinates of (n-1)-cube with both a 0 added and a 1 added
smbelcas 2019-03-18 19:58:49
People think that the corners of an $n$-cube can be described as all $n$-tuples with entries that are $0$ or $1$. But this is a conjecture...
smbelcas 2019-03-18 19:58:51
...and so here are more questions. Can you prove that an $n$-cube has $2^n$ corners? Are you sure that every corner of an $n$-cube should have coordinates with entries that are $0$ or $1$; why? Does every $n$-tuple with $0$ and/or $1$ entries represent a corner of an $n$-cube?
smbelcas 2019-03-18 20:00:09
These questions are much tougher, but here is where we are really getting to understand the $n$-cube. Let's answer them one at a time.
smbelcas 2019-03-18 20:00:11
Prove that an $n$-cube has $2^n$ corners.
MrMXS 2019-03-18 20:01:00
it has $2^{n}$ corners by induction since at each step we "copy" our previous cube, going from $v$ vertices to $2v$ vertices
ChickenAgent2227-_- 2019-03-18 20:01:00
Yes, by induction. Every time you sweep an n-1 cube it you make a copy of it and have double the vertices in an n cube
DOGSTREET1 2019-03-18 20:01:00
yes, because you double the number of corners every time you moosh the cube
mandrake41 2019-03-18 20:01:00
Each time you moosh an n cube to an n+1 cube, you double the number of corners. One for the starting position and one for the ending position.
spoamath321 2019-03-18 20:01:00
Yes, a 0-cube (not really a cube) is 2^0, a 1-cube is 2^1 points
rubixsolver 2019-03-18 20:01:00
Every time we moosh an n-cube, we double the number of corners it has. This results in (current number of corners * 2) which is doubling it.
cad314 2019-03-18 20:01:06
verticies always double everytime we add a dimension because we are just copying the (n-1)-cube and connecting all the verticies
smbelcas 2019-03-18 20:01:07
When we make an $n$-cube from an $(n-1)$-cube, we moosh that $(n-1)$-cube by one unit. There are the "starting" corners and the "ending" corners, so there are twice as many corners in an $n$-cube as in an $(n-1)$-cube.
smbelcas 2019-03-18 20:01:20
That's not enough to say that the number of corners is $2^n$, though. We also have to remember that we can manually count to see that the number of corners of the $\{0$-cube, $1$-cube, $2$-cube, $3$-cube$\}$ is $\{1, 2, 4, 8\}$ so if we continue to double we'll always get $2^n$.
smbelcas 2019-03-18 20:01:36
Are you sure that every corner of an $n$-cube should have coordinates with entries that are $0$ or $1$; why?
ad46578 2019-03-18 20:02:41
if it has a corner on the origin, then yes because the corners must always be 1 unit away from the origin
spoamath321 2019-03-18 20:02:41
It starts with one point and the unit increases by one
cad314 2019-03-18 20:02:41
because all the side lengths are always 1 (why they are cubes)
mandrake41 2019-03-18 20:02:41
since each time you moosh in a perpendicular direction, you will only ever reach a maximum of 1 for any corner; corners that are already at 1 for one axis will never go past 1 on that dimension
Damalone 2019-03-18 20:02:41
Because mooshing is a type of Cartesian product as you said
ChickenAgent2227-_- 2019-03-18 20:02:41
yes, you just moosh it 1 unit in the next dimension, so if each previous cube has coordinates with entries that are all 0 or 1, then each new cube should have those, but with 0 or 1 added on at the end
smbelcas 2019-03-18 20:02:43
The corners of an $n$-cube must have coordinate entries that are $0$ or $1$ if we situate our original point at $0$, because every corner is either a "starting" corner ($0$ entry) or an "ending" corner ($1$ entry) in the last coordinate, and has the $0$ and/or $1$ entries from lower-dimensional cubes in the first $n-1$ coordinates.
smbelcas 2019-03-18 20:02:56
Does every $n$-tuple with $0$ and/or $1$ entries represent a corner of an $n$-cube?
Allen31415 2019-03-18 20:04:16
Every direction has an axis, each axis can have two possible coordinates
mandrake41 2019-03-18 20:04:16
As you increase the dimensions of a cube, the number of corners double, as do the number of combinations of 1s and 0s. Since each corner ends up in a different location, this means that each combination of 1s and 0s are used.
ChickenAgent2227-_- 2019-03-18 20:04:16
yes, there are 2^n such n-tuples and each corresponds to a corner, which there are 2^n of
Allen31415 2019-03-18 20:04:16
Yes, it is a 1-1 correspondence between the coordinates and vertices on an $n$-cube.
smbelcas 2019-03-18 20:04:20
One way we can say that every $n$-tuple with $0$ and/or $1$ entries represents a corner of an $n$-cube is by using our previous two arguments: There are $2^n$ $n$-tuples with $0$ and/or $1$ entries, and every corner must be among them. However, there are also $2^n$ corners, so each of those $n$-tuples represents a corner!
MrMXS 2019-03-18 20:04:28
yeah cause for each dimension and for each vertex that vertex was either translated or not translated in that dimension, which correspond to a $1$ and a $0$, respectively (and we represent this by having each coordinate correspond to a dimension/translation)
da-rong_wae 2019-03-18 20:04:32
Suppose one isnt, then we have 2^n corners but fewer n-tuples
smbelcas 2019-03-18 20:04:48
Now let's count parts of $n$-cubes: Please help to fill in the table:
smbelcas 2019-03-18 20:04:52
$$\begin{array}{c||c|c|c|c|c|c|c}
{\rm dim} &0&1&2&3&4&5&\dots\\ \hline
\hline
{\rm points} & 1 &2&&& &&\dots\\
\hline
{\rm lines} &0 &1 & & & & &\dots\\
\hline
{\rm squares} &0 &0 & & & & &\dots\\
\hline
{\rm 3-cubes} &0 &\hspace{1cm} & & & & &\dots\\
\hline
{\rm 4-cubes}&\hspace{1cm} &0 &\hspace{1cm}&\hspace{1cm}&\hspace{1cm}&\hspace{1cm}&\dots\\
\hline
\end{array}$$
smbelcas 2019-03-18 20:04:56
So, for example, you can say "points in $2$-cube is $4$" to fill in the next entry of the "points" row.
smbelcas 2019-03-18 20:06:39
I'll pass the answers through, column by column.
smbelcas 2019-03-18 20:06:48
For $2$-cubes:
mjz6202007 2019-03-18 20:06:50
squares in 2-cube is 1
ChickenAgent2227-_- 2019-03-18 20:06:50
points in $2$-cube is $4$
cad314 2019-03-18 20:06:50
lines in 2-cube is 4
cad314 2019-03-18 20:06:50
squares in 2-cube is 1
avisioner 2019-03-18 20:06:50
lines in 2 cube is 4
DOGSTREET1 2019-03-18 20:06:50
lines in 2 cube is 4
DOGSTREET1 2019-03-18 20:06:50
squares in 2 cube is 1
mjz6202007 2019-03-18 20:06:50
lines in 2-cube is 4
karthik_malasani 2019-03-18 20:07:11
2 dimensions: points = 4, lines = 4, squares = 1, 3-cubes = 0, 4-cubes = 0
smbelcas 2019-03-18 20:07:44
For $3$-cubes:
mandrake41 2019-03-18 20:07:46
lines in 3-cube is 12
mandrake41 2019-03-18 20:07:46
squares in 3-cube is 6
Mathlete161 2019-03-18 20:07:46
squares in 3 cubes is 6
mjz6202007 2019-03-18 20:07:46
points in 3-cube is 8
avisioner 2019-03-18 20:07:46
points in 3-cube is 8
mjz6202007 2019-03-18 20:07:46
lines in 3-cube is 12
avisioner 2019-03-18 20:07:46
lines in 3 cube is 12
DOGSTREET1 2019-03-18 20:07:46
points in 3 cube is 8
cad314 2019-03-18 20:07:46
points in 3-cube is 8
DOGSTREET1 2019-03-18 20:07:46
lines for 3 cube is 12
DOGSTREET1 2019-03-18 20:07:46
squares in 3 cube 6
DOGSTREET1 2019-03-18 20:07:46
3 cubes in 3 cube is 1
mandrake41 2019-03-18 20:07:46
3-cubes in 3-cube is 1
karthik_malasani 2019-03-18 20:08:31
3- dimensions: points = 8, lines = 12, squares = 6, 3-cubes = 1, 4-cubes = 0
smbelcas 2019-03-18 20:09:25
For $4$-cubes:
avisioner 2019-03-18 20:09:27
points in 4 cube is 16
karthik_malasani 2019-03-18 20:09:27
4- dimensions: points = 2^4 = 16, lines = 4*2^3 = 32, squares = 12?, 3-cubes = 2, 4-cubes = 1
DOGSTREET1 2019-03-18 20:09:27
points in 4 cube is 16
ChickenAgent2227-_- 2019-03-18 20:09:27
4-cubes in 4-cube is 1
Allen31415 2019-03-18 20:09:27
$3$-cubes in 4-cube is 8
StickyWashington 2019-03-18 20:09:27
points in 4-cube is 16
DOGSTREET1 2019-03-18 20:09:27
4 cube in 4 cube is 1
Allen31415 2019-03-18 20:09:27
Lines in 4-cube is 32
Allen31415 2019-03-18 20:09:27
points in 4-cube is 16
ChickenAgent2227-_- 2019-03-18 20:09:27
3-cubes in 4-cube is 8?
smbelcas 2019-03-18 20:10:29
For $5$-cubes:
mandrake41 2019-03-18 20:10:31
points in 5-cube is 32
ad46578 2019-03-18 20:10:31
points in 5- cube is 32
avisioner 2019-03-18 20:10:31
points in 5 cube is 32
als123 2019-03-18 20:10:31
points in 5-cube is 32
DOGSTREET1 2019-03-18 20:10:31
points in 5 cube is 32
avisioner 2019-03-18 20:11:04
lines in a 5d cube is 80
Allen31415 2019-03-18 20:11:04
lines in 5 cube is 80
mandrake41 2019-03-18 20:11:04
5-cubes in 5-cube is 1
avisioner 2019-03-18 20:11:04
5d cube has 80 lines
Allen31415 2019-03-18 20:11:04
3-cubes in 5-cube is 40
smbelcas 2019-03-18 20:11:07
Wait a minute. Where are those numbers coming from? Did you draw a $5$-cube earlier, and have been counting from it?
DOGSTREET1 2019-03-18 20:11:30
nope
avisioner 2019-03-18 20:11:30
no!
mandrake41 2019-03-18 20:11:30
...maybe
smbelcas 2019-03-18 20:11:32
I'm just not sure of all those numbers. Well, here is the updated table:
smbelcas 2019-03-18 20:11:33
$$\begin{array}{c||c|c|c|c|c|c|c}
{\rm dim} &0&1&2&3&4&5&\dots\\ \hline
\hline
{\rm points} & 1 &2&4&8&16&32&\dots\\
\hline
{\rm lines} &0 &1 &4 &12 &32 & &\dots\\
\hline
{\rm squares} &0 &0 &1 &6 &24 & &\dots\\
\hline
{\rm 3-cubes} &0 &0 &0 &1 &8 & &\dots\\
\hline
{\rm 4-cubes}&0 &0 &0 &0 &1 & &\dots\\ \hline
&\hspace{1cm} &\hspace{1cm}&\hspace{1cm}&\hspace{1cm}&\hspace{1cm}&\hspace{1cm}& \\
\end{array}$$
smbelcas 2019-03-18 20:11:40
The $5$-cube numbers are mostly left out because I'm just not convinced yet.
smbelcas 2019-03-18 20:11:46
Let me give you some notation: Let $C_n$ denote the $n$-cube.
smbelcas 2019-03-18 20:11:52
And let $f_k(C_n) = $ the number of $k$-cubes in $C_n$. (The $f$ stands for $f$aces.)
smbelcas 2019-03-18 20:12:08
We already proved that $f_0(C_n) = 2^n$. Do you have any conjectures based on the data we have in the table?
Allen31415 2019-03-18 20:14:50
$f_1(C_n)=n \cdot 2^{n-1}$
MrMXS 2019-03-18 20:14:50
$f_{1}(C_{n})=2f_{1}(C_{n-1})+2^{n-1}$
ChickenAgent2227-_- 2019-03-18 20:14:50
$f_1(C_n) = n\cdot 2^{n-1}$
mandrake41 2019-03-18 20:14:50
f1(cn) = n * 2^n
da-rong_wae 2019-03-18 20:14:50
F0(c_(n+1))=2f0(c_n)
ChickenAgent2227-_- 2019-03-18 20:14:50
$f_2(C_n) = n(n-1)\cdot 2^{n-3}$
jerry_yang 2019-03-18 20:14:50
f_1(C_n)=n*2^(n-1)
ChickenAgent2227-_- 2019-03-18 20:14:50
$f_3(C_n) = n(n-1)(n-2)\cdot 2^{n-3}$
mandrake41 2019-03-18 20:14:50
f1(cn) = n * 2^(n-1)
ChickenAgent2227-_- 2019-03-18 20:14:50
sum of columns is 3^n!
DoingWhatCounts 2019-03-18 20:14:50
coefficients in expansion of (1 + 2)^n
smbelcas 2019-03-18 20:15:58
These are interesting.
smbelcas 2019-03-18 20:16:16
Does anyone have a conjecture for what $f_k(C_n)$ is?
smbelcas 2019-03-18 20:16:26
Either in terms of smaller cubes or faces, or directly?
da-rong_wae 2019-03-18 20:18:04
N!/k!*2^n-k
MrMXS 2019-03-18 20:18:04
$f_{k}(C_{n})=\cfrac{n!}{(n-k)!}2^{n-k}$?? Kind of a guess
da-rong_wae 2019-03-18 20:18:04
M!/(n-k)!*2^n-k
smbelcas 2019-03-18 20:18:09
These are all close.
smbelcas 2019-03-18 20:18:31
Any ideas for a recurrence?
smbelcas 2019-03-18 20:19:15
Here are cleaned-up versions of what some of you have been saying:
smbelcas 2019-03-18 20:19:19
Conjecture 1: $f_k(C_n) = 2f_k(C_{n-1})+f_{k-1}(C_{n-1})$.
smbelcas 2019-03-18 20:19:24
Conjecture 2: $f_k(C_n) = {n\choose k}2^{n-k}$. (This one only makes sense if you know binomial coefficients already.)
smbelcas 2019-03-18 20:19:38
Conjecture 3: The sum of the $n$-th column is $3^n$.
smbelcas 2019-03-18 20:19:44
Can you prove any of these?
smbelcas 2019-03-18 20:20:54
Conjecture 1 follows from our construction of the $n$-cube. How does that work, exactly?
smbelcas 2019-03-18 20:21:28
Let's go through the details. What happens to a corner point when we moosh?
Allen31415 2019-03-18 20:22:07
It copies itself, creating an edge.
smbelcas 2019-03-18 20:22:10
It turns into a line segment. Basically it has the "starting" (or $0$) point, and the "ending" (or $1$) point, and the trail left is a line segment.
mandrake41 2019-03-18 20:22:17
copies, creating a line
smbelcas 2019-03-18 20:22:20
What happens to a line segment when we moosh?
ChickenAgent2227-_- 2019-03-18 20:22:51
creates a face
mandrake41 2019-03-18 20:22:51
copies, creating a 2-cube
Allen31415 2019-03-18 20:22:51
It copies itself, creating a square.
gozomete 2019-03-18 20:22:51
creats a square
mjz6202007 2019-03-18 20:22:51
It copies itself and moves perpendicular to the original shape, leaving the trail it took to get to the new shape.
MrMXS 2019-03-18 20:22:51
gives us a square
smbelcas 2019-03-18 20:22:54
It turns into a square. Basically it has the "starting" (or $0$) segment, and the "ending" (or $1$) segment, and the trail left is a square.
smbelcas 2019-03-18 20:22:56
What happens to a square when we moosh?
cad314 2019-03-18 20:23:12
and a plane becomes a cube
Allen31415 2019-03-18 20:23:12
It copies itself, creating a cube
mandrake41 2019-03-18 20:23:12
creates a cube
ChickenAgent2227-_- 2019-03-18 20:23:12
It copies itself and makes a cube
cad314 2019-03-18 20:23:12
a square becomes a cube
phanithans1 2019-03-18 20:23:12
into a cube
smbelcas 2019-03-18 20:23:13
It turns into a $3$-cube. Basically it has the "starting" (or $0$) square, and the "ending" (or $1$) square, and the trail left is a $3$-cube.
smbelcas 2019-03-18 20:23:16
So, more generally, what happens to a $k$-cube when we moosh?
MrMXS 2019-03-18 20:23:39
a $k$-dimensional object gives us a $(k+1)$-dimensional object
Allen31415 2019-03-18 20:23:39
It copies itself, creating a $k+1$-cube.
mandrake41 2019-03-18 20:23:39
k+1 cube
ChickenAgent2227-_- 2019-03-18 20:23:39
It copies itself and makes a k+1 cube
da-rong_wae 2019-03-18 20:23:39
Becomes k+1 cube
spoamath321 2019-03-18 20:23:39
it becomes a k+1 cube
gozomete 2019-03-18 20:23:39
k+1-cube
smbelcas 2019-03-18 20:23:41
It turns into a $(k+1)$-cube. Basically it has the "starting" (or $0$) $k$-cube, and the "ending" (or $1$) $k$-cube, and the trail left is a $(k+1)$-cube.
smbelcas 2019-03-18 20:23:44
How does that help us prove Conjecture 1?
smbelcas 2019-03-18 20:24:23
The formula says the number of $k$-cubes in an $n$-cube is the same as $2($the number of $k$-cubes in an $(n-1)$-cube$) + ($the number of $(k-1)$-cubes in an $(n-1)$-cube$)$.
da-rong_wae 2019-03-18 20:24:42
We count twice everything in previous step, cuz we are copying the whole Cn, then account for the "mooshed" stuff
smbelcas 2019-03-18 20:25:00
The $2($the number of $k$-cubes in an $(n-1)$-cube$)$ counts the "starting" and "ending" $k$-cubes from a moosh.
mandrake41 2019-03-18 20:25:17
everything is doubled, plus the k-1 cubes are mooshed into k cubes
MrMXS 2019-03-18 20:25:17
the number of $k$-dimensional objects is twice the number of $k$-dimensional objects in our previous cube (because it's copied) plus all of the $(k-1)$ dimensional stuff which becomes $k$-dimensional stuff
ChickenAgent2227-_- 2019-03-18 20:25:17
Each k-dimesnional face of a n-cube can be a new one made from mooshing, or an old one that alredy existed. The new ones are made from each $k-1$ D face of the old cube. The old ones are the k-D faces from the old cube, copies to have 2 times as much
smbelcas 2019-03-18 20:25:22
The $($the number of $(k-1)$-cubes in an $(n-1)$-cube$)$ counts the new $k$-cubes from the moosh, which all came from the trails of $(k-1)$-cubes.
cad314 2019-03-18 20:25:26
the first term is that every one of the objects gets duplicated from the (n-1)-cube, the second term is that everything that is (k-1)-cube becomes 1 k-cube
smbelcas 2019-03-18 20:25:38
Conjecture 2 is tougher, so we won't discuss it tonight.
smbelcas 2019-03-18 20:26:04
But we can use Conjecture 1 to prove Conjecture 3. Do you see how?
ChickenAgent2227-_- 2019-03-18 20:26:46
induction and adding everything up?
Allen31415 2019-03-18 20:26:46
induction?
sansae 2019-03-18 20:26:46
Just a induction!
MrMXS 2019-03-18 20:26:46
induction?
da-rong_wae 2019-03-18 20:26:46
Telescopic sums?
smbelcas 2019-03-18 20:26:57
Before working on Conjecture 3, let's restate it in mathematical notation: $\sum_{k=0}^n f_k(C_n)= 3^n.$
smbelcas 2019-03-18 20:27:29
We'll use Conjecture 1: $\sum_{k=0}^n f_k(C_n) = \sum_{k=0}^n 2f_k(C_{n-1})+f_{k-1}(C_{n-1})$.
smbelcas 2019-03-18 20:27:38
What can we do?
ChickenAgent2227-_- 2019-03-18 20:28:00
Split into two sums
smbelcas 2019-03-18 20:28:01
If we distribute, we have $\sum_{k=0}^n 2f_k(C_{n-1})+ \sum_{k=0}^nf_{k-1}(C_{n-1})$.
smbelcas 2019-03-18 20:28:24
So that's $2$ times the total sum for an $(n-1)$-cube, plus another sum that represents all that stuff from the mooshing. What is that sum from the mooshing?
ChickenAgent2227-_- 2019-03-18 20:28:35
reindex
smbelcas 2019-03-18 20:28:43
$\sum_{k=0}^nf_{k-1}(C_{n-1}) = \sum_{k=0}^nf_{k}(C_{n-1}) $ because the first term on the left-hand side is just $0$, and the last term on the right-hand side is also $0$. Why?
smbelcas 2019-03-18 20:29:30
There are no $(-1)$-cubes! And there are no $n$-cubes in an $(n-1)$-cube.
smbelcas 2019-03-18 20:29:35
So now our total sum is $\sum_{k=0}^n2f_k(C_{n-1})+f_k(C_{n-1}) = 3 \sum_{k=0}^nf_k(C_{n-1})$.
smbelcas 2019-03-18 20:29:51
Just one more step---how do we finish the proof?
Allen31415 2019-03-18 20:30:19
Base Case when $n=0$
MrMXS 2019-03-18 20:30:19
look at the sum in the first column
smbelcas 2019-03-18 20:30:21
Because our first few sums are powers of $3$, that pattern continues.
smbelcas 2019-03-18 20:30:51
There is also a neat proof based on Conjecture 2---you can think about that later.
smbelcas 2019-03-18 20:30:55
Okay, let's switch gears and talk about {MathILy, MathILy-Er} so that there's time for you to ask lots of questions. (I hope you enjoyed the math!)
smbelcas 2019-03-18 20:31:07
{MathILy, MathILy-Er} are intensive residential summer programs for mathematically excellent secondary students.
smbelcas 2019-03-18 20:31:14
As we say on the website (http://www.mathily.org), {MathILy, MathILy-Er} focus on participants exploring and creating mathematics. Instructors provide the framework and you get to make (and prove!) the conjectures. You will encounter new ideas, improve your problem-solving skills, learn lots and lots of advanced mathematics, and hone your overall thinking skills. You'll meet others like you. (Yes, really. We promise.) Most of all, you will find serious mathematics infused with levity.
{MathILy, MathILy-Er} are five weeks of maximized mathematical marvelousness.
smbelcas 2019-03-18 20:31:30
The programs share an application process---you apply to both programs at once. You take an Exam Assessing Readiness and fill out some information on the Short Form and Not-as-Short Form. Based on these things (and comments from a recommender) the {MathILy, MathILy-Er} Directors decide whether you are qualified, and if so, for which program. MathILy-Er is designed for students who are a little bit earlier in their mathematical development than MathILy students.
smbelcas 2019-03-18 20:31:46
Please ask questions!
Potato12 2019-03-18 20:31:50
what are the combined admission rates of mathily and mathily EAR? If we don't solve all the problems do we still have a chance of getting in?
smbelcas 2019-03-18 20:32:09
I don't know what you mean by "combined admission rates." But no one solves all the problems correctly.
spoamath321 2019-03-18 20:32:17
How long is it?
smbelcas 2019-03-18 20:32:20
5 weeks!
ibtstrash_ 2019-03-18 20:32:23
What ages are these programs for?
smbelcas 2019-03-18 20:32:40
We focus on 14--17, but we take applications from younger and older students.
smbelcas 2019-03-18 20:33:02
That said, we haven't admitted anyone younger than 13 (no one has done well enough on the EAR) or older than 18.
Potato12 2019-03-18 20:33:07
Like out of all the students who apply, what are the percentage of those accepted?
smbelcas 2019-03-18 20:33:17
Last year it was something like 20%.
smbelcas 2019-03-18 20:33:21
I think this year it will be lower.
Allen31415 2019-03-18 20:33:31
Have you been in MathILY, and is it fun?
smbelcas 2019-03-18 20:33:39
Yes, always, and yes, always.
Potato12 2019-03-18 20:33:43
Are the admissions rolling?
smbelcas 2019-03-18 20:33:46
Yup.
cad314 2019-03-18 20:33:50
What typical high school courses are helpful as prerequisites for {MathILy, MathILy-Er} respectively?
mjz6202007 2019-03-18 20:33:50
Around what grade level material are most of the problems centered around?
BeastAtMath12 2019-03-18 20:33:50
Are there any middle schoolers there?
smbelcas 2019-03-18 20:34:07
We don't have prerequisites, or grade-level material. There are sometimes middle-schoolers.
SandyK 2019-03-18 20:34:17
@Allen I've gone to MathILy-Er twice. Oh yeah. Best experience of my life.
Allen31415 2019-03-18 20:34:32
Are the questions in the program roughly the same level as the conjectures we just have proven?
smbelcas 2019-03-18 20:34:40
OOh! great question!
smbelcas 2019-03-18 20:34:48
The problems in the program are much harder.
Potato12 2019-03-18 20:35:00
What is the percentage of applicants accepted to just Mathily?
smbelcas 2019-03-18 20:35:17
Something like 20%, and then there's another selection process for MathILy-Er that's roughly the same.
ww1234 2019-03-18 20:35:21
Is the flavor of the camp more "fun" type that touch different variety of topics in discrete math? or is the camp more systematic and goes in depth like AoPS classes?
smbelcas 2019-03-18 20:35:25
All of the above!
DOGSTREET1 2019-03-18 20:35:32
Do you get to choose what you learn?
smbelcas 2019-03-18 20:35:41
During some parts of the program, yes; during other parts,no.
phanithans1 2019-03-18 20:35:46
why will the percent of applicants passing be lower this year?
smbelcas 2019-03-18 20:35:57
More applications, and fewer of those are qualified.
mgrimalo 2019-03-18 20:36:01
What is the dorm situation at the college? (Room accompaniment, curfew, rule strictness, etc.)
smbelcas 2019-03-18 20:36:16
I don't know how to answer that. But it's kind of like college.
ww1234 2019-03-18 20:36:22
Are there lots of exercises and problems in addition to classroom introduction/discussion?
smbelcas 2019-03-18 20:36:39
This... we don't have that kind of classroom.
smbelcas 2019-03-18 20:36:44
It's all mixed together.
smbelcas 2019-03-18 20:36:50
We do problems in class.
ww1234 2019-03-18 20:36:52
What is the percentage of girls in the past?
smbelcas 2019-03-18 20:37:17
That's varied from year to year. Often it's near 1/3. I hope it will be more this year.
Potato12 2019-03-18 20:37:29
What is the cost of the program? And is there a significant amount of financial aid provided?
smbelcas 2019-03-18 20:37:56
$4600 and all financial aid is need-based. We expect that we'll be able to meet all demonstrated need, as we have in the past several years.
ibtstrash_ 2019-03-18 20:37:59
What level of math is taught in the programs?
smbelcas 2019-03-18 20:38:02
college.
smbelcas 2019-03-18 20:38:06
And sometimes graduate.
ww1234 2019-03-18 20:38:09
Does the dorm has AC? Are there different cafeteria open during the camp and different variety of food available?
smbelcas 2019-03-18 20:38:28
At MathILy, there are room ACs and at MathILy-Er the weather is cool so no AC is needed.
smbelcas 2019-03-18 20:38:45
There is exactly one dining hall for each campus and it has lots of different interesting food.
Allen31415 2019-03-18 20:38:50
Where and when can I take this EAR exam?
del-math 2019-03-18 20:38:50
Is the exam the same every year, or does it change?
smbelcas 2019-03-18 20:39:04
You can take the EAR, new every year, by submitting a Short Form on the website.
BeastAtMath12 2019-03-18 20:39:12
Is the application process done for this year?
smbelcas 2019-03-18 20:39:16
HA HA HA HA HA no.
mandrake41 2019-03-18 20:39:19
How long will applications be open for
smbelcas 2019-03-18 20:39:24
At least until April 23rd.
smbelcas 2019-03-18 20:39:29
And then after, if there are spaces left.
Damalone 2019-03-18 20:39:38
How does this compare to Mathcamp?
smbelcas 2019-03-18 20:39:48
Good question. It's philosophically very different.
smbelcas 2019-03-18 20:40:00
Mathcamp has everything optional, and focuses on forming community.
smbelcas 2019-03-18 20:40:13
MathILy and MathILy-Er have everything required, and focus on learning a lot.
smbelcas 2019-03-18 20:40:20
We are sillier than Mathcamp is.
ww1234 2019-03-18 20:40:27
How long will we hear back after submit the application?
smbelcas 2019-03-18 20:40:39
Usually about a week, but sometimes two or more during heavy admissions times.
del-math 2019-03-18 20:40:46
Is there an age limit? I know you said 13-ish to 18-ish, but is there an age where you draw the line?
smbelcas 2019-03-18 20:41:04
We tend not to draw lines except on chalkboards.
Potato12 2019-03-18 20:41:08
Where are the locations of the programs?
smbelcas 2019-03-18 20:41:12
MathILy: Bryn Mawr.
smbelcas 2019-03-18 20:41:18
MathILy-Er: Bowdoin.
Allen31415 2019-03-18 20:41:25
If I got a 6 on the AIME, is it possible for me to make the program?
smbelcas 2019-03-18 20:41:35
How would I know? I know nothing about contests or scoring them.
ww1234 2019-03-18 20:41:41
How different is MathIly compared with Promys?
smbelcas 2019-03-18 20:41:46
Extremely different.
smbelcas 2019-03-18 20:42:00
At PROMYS the focus is on number theory, and at MathILy the focus is on discrete math.
smbelcas 2019-03-18 20:42:30
At PROMYS there are problem sets done independently. At MathILy we do pretty much everything communally.
ChickenAgent2227-_- 2019-03-18 20:42:34
do you teach at MathIly?
smbelcas 2019-03-18 20:42:44
Yes, ChickenAgent. I've taught there every summer and I run the program.
ww1234 2019-03-18 20:42:49
But depth are similar other than the topics?
smbelcas 2019-03-18 20:42:52
Yes.
mgrimalo 2019-03-18 20:42:56
Are there ever one-on-one sessions with the instructors? Maybe something like office hours?
smbelcas 2019-03-18 20:43:00
Yes, and no.
smbelcas 2019-03-18 20:43:11
That is, there are constantly one-on-one sessions, but not office hours.
smbelcas 2019-03-18 20:43:43
We talk to students approximately all the time. Well, actually, we listen to them. And then ask them questions after they've also talked to each other.
Potato12 2019-03-18 20:43:47
Should I wait to submit my application after I receive my AIME score or will it not make a big difference?
smbelcas 2019-03-18 20:44:02
If you're even asking that question, I think you maybe haven't read my earlier responses...
aopsUserNY 2019-03-18 20:44:13
What is the daily schedule like?
smbelcas 2019-03-18 20:44:22
Morning class: 4 hours.
smbelcas 2019-03-18 20:44:25
Evening class: 3 hours.
smbelcas 2019-03-18 20:44:31
Daily Gather in the late afternoon.
smbelcas 2019-03-18 20:44:35
And meals. Three of them.
smbelcas 2019-03-18 20:44:41
Also optional bedtime stories.
gozomete 2019-03-18 20:44:47
what type of math do you do at mathily-er?
smbelcas 2019-03-18 20:45:08
Very similar to what is done at MathILy, and yet totally different. That is, both programs do discrete math but do different parts of it.
ChickenAgent2227-_- 2019-03-18 20:45:12
Do earlier applicants have higher priority?
smbelcas 2019-03-18 20:45:40
We have rolling admissions, so not really. The only way in which earlier applicants have priority is if we were to run out of spots, which we never do before our "deadline."
spoamath321 2019-03-18 20:45:55
Do you stay there for 5 weeks?
smbelcas 2019-03-18 20:46:03
I do. I live in the dorms with the students, as do all instructors.
Allen31415 2019-03-18 20:46:12
What are the dates of the program?
smbelcas 2019-03-18 20:46:33
Uhhh.... I think June 30 to August 3? Check the website (I would have to check in order to be sure).
ChickenAgent2227-_- 2019-03-18 20:46:36
how many days a week are there classes?
smbelcas 2019-03-18 20:46:44
5.5 days per week.
smbelcas 2019-03-18 20:47:15
We have morning/evening class and Daily Gather Monday--Friday, and morning class on Saturday, and then Life Seminar on Saturday afternoon.
cad314 2019-03-18 20:47:19
what do students do on the days without classes?
smbelcas 2019-03-18 20:47:44
Depends on the day. We have big activities on some of the days. On others people play games and stuff.
smbelcas 2019-03-18 20:47:52
But people also play games and stuff on class days.
smbelcas 2019-03-18 20:47:53
So.
StickyWashington 2019-03-18 20:47:56
I play saxophone. Would I have time and a place to practice every day?
smbelcas 2019-03-18 20:48:26
Time? Yes. Place? Depends on how private you want it to be. We usually have a practice room, and people sign it out for various times.
Waterfall1234 2019-03-18 20:48:29
What is the difference between Mathily and Mathily-er
smbelcas 2019-03-18 20:48:51
MathILy-Er is for students who are slightly younger in their mathematical development.
aopsUserNY 2019-03-18 20:48:58
Is there access to an athletic center?
smbelcas 2019-03-18 20:49:16
Yes, of sorts. Some of the parts can only be accessed with a staff member around.
Allen31415 2019-03-18 20:49:20
Is there an electronic policy?
smbelcas 2019-03-18 20:49:31
What is an electronic policy? One that we post on the internet?
Damalone 2019-03-18 20:49:38
what are some advantages of this over other math camps?
smbelcas 2019-03-18 20:49:45
That depends on who you are.
smbelcas 2019-03-18 20:50:10
The different math programs fit different people well.
smbelcas 2019-03-18 20:50:39
We do inquiry-based learning at MathILy and MathILy-Er, so students who like to invent math and discuss their ideas are well suited to our approach.
smbelcas 2019-03-18 20:50:45
Students who are gooftastic also tend to fit in.
Potato12 2019-03-18 20:51:08
Will there be shuttles to take people from the airport to the site?
smbelcas 2019-03-18 20:51:17
No, just cars and trains and vans.
smbelcas 2019-03-18 20:51:23
We don't have access to the space program.
ww1234 2019-03-18 20:52:49
Will the program help to pickup kids flying unaccompanied minor?
smbelcas 2019-03-18 20:52:55
As much as we can, yes!
smbelcas 2019-03-18 20:53:14
Usually if someone needs to fly unaccompanied minor, our Minion works with the family to arrange things in advance.
PracticingMath 2019-03-18 20:53:23
Do they provide resources, for example food?
smbelcas 2019-03-18 20:53:33
Does *who* provide resources?
Potato12 2019-03-18 20:54:04
If I submit within the next three days, will I get my decision back within a week or is this a busy time?
smbelcas 2019-03-18 20:54:15
That depends on how easy the decision is
phanithans1 2019-03-18 20:54:26
what about unacomppannied major
smbelcas 2019-03-18 20:54:41
That's a pretty good question. I think there is a piano in our dorm, or maybe two?
smbelcas 2019-03-18 20:54:48
So no need for unaccompanied majors.
casi 2019-03-18 20:55:18
What's the minimum age?
smbelcas 2019-03-18 20:55:34
We don't do minimums, or deadlines, or (for the most part) rules.
smbelcas 2019-03-18 20:55:42
We just do stuff that makes sense.
smbelcas 2019-03-18 20:56:09
I think I might have missed some questions earlier.
smbelcas 2019-03-18 20:56:21
If I didn't answer something you tried to ask, please try again now!
cooljoseph 2019-03-18 20:56:43
How hard are the classes?
smbelcas 2019-03-18 20:56:54
Super-hard! Also not that hard.
bkim0325 2019-03-18 20:56:57
will we be doing original research?
smbelcas 2019-03-18 20:57:18
No. That's for research programs. I don't think we've ever had a student who arrived qualified to do research.
pad 2019-03-18 20:57:25
where can I find the ear for mathily?
smbelcas 2019-03-18 20:57:28
You can't!
cooljoseph 2019-03-18 20:57:33
Hard is relative. What do you mean by hard? Is it harder than AIME level questions?
smbelcas 2019-03-18 20:57:43
I know nothing about math contests.
Potato12 2019-03-18 20:57:52
Since it's 20% for mathily and 20% for mathilyear, does that mean there is about a 40% admittance rate to either program?
smbelcas 2019-03-18 20:58:01
There are a lot of ways of measuring.
smbelcas 2019-03-18 20:58:21
Because the missions of the programs are slightly different, it's not quite additive.
Damalone 2019-03-18 20:58:36
is this a good way to prepare myself for a research program?
smbelcas 2019-03-18 20:58:39
Yes!
smbelcas 2019-03-18 20:58:55
It's an excellent way, because we structure our classrooms to be research-like experiences.
Potato12 2019-03-18 20:58:59
If we get rejected but there are spots open at the end or if someone drops out, can we still join?
smbelcas 2019-03-18 20:59:18
Nope. If you're not admitted, then it's generally because you're not qualified this year.
cad314 2019-03-18 20:59:41
is there a waitlist?
smbelcas 2019-03-18 20:59:46
If we fill up near the "deadline", we will make a waitlist.
smbelcas 2019-03-18 21:00:10
So far we've managed to avoid an actual waitlist by asking people to make decisions more quickly.
Potato12 2019-03-18 21:00:13
So there's no advantage towards applying early?
smbelcas 2019-03-18 21:00:18
You get a decision earlier!
Potato12 2019-03-18 21:00:43
I mean like application-wise, is there a higher chance we will be admitted?
smbelcas 2019-03-18 21:00:46
Nope.
smbelcas 2019-03-18 21:01:34
Okay! Any last questions?
Waterfall1234 2019-03-18 21:02:31
Would the program be too hard for people who aren't very experienced in proofs?
smbelcas 2019-03-18 21:02:58
That depends on the person. Some people have no experience in proofs and do really well. Others can't handle it. That's why we have the EAR!
gozomete 2019-03-18 21:03:01
Is Mathil-er online?
smbelcas 2019-03-18 21:03:05
Nope, it's in person.
smbelcas 2019-03-18 21:04:20
Okay, I'm not hearing any more questions, so I think that's about it!
smbelcas 2019-03-18 21:04:30
Thanks for coming to the {MathILy, MathILy-Er} Math Jam.
StickyWashington 2019-03-18 21:04:33
Thanks for the class!
smbelcas 2019-03-18 21:04:37
You are super welcome!
smbelcas 2019-03-18 21:04:47
As a reminder, the website is http://www.mathily.org

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