[Question]
  [
It has been proven that the following 13 square [Wang tiles](http://en.wikipedia.org/wiki/Wang_tile) always tile the plane [aperiodically](http://en.wikipedia.org/wiki/Aperiodic_tiling). This means that when the squares are arranged in a grid with all neighboring sides the same color, a translation of the pattern will never match up with itself.
![Wang tiles](https://i.stack.imgur.com/F249x.png)
We'll represent each tile textually by a 3×3 grid filled with spaces at the center and corners, and the numbers 1 through 5 instead of the colors red, green, blue, yellow, grey, at the edges:
```
 2      2      2      1      1      1      4      3      2      2      4      3      2
1 2    1 3    2 3    2 1    3 1    3 2    4 4    4 4    4 5    4 5    5 5    5 5    5 4
 3      2      3      2      3      2      1      2      1      4      1      2      2
```
# Goal
Your task is to write a program that takes in a width and height and outputs a valid Wang tile grid with those dimensions. A valid tiling is one in which all the adjacent tile edges have the same color (or number). The smallest program in bytes wins.
Your input should come from stdin or command line arguments and output should go to stdout. The exact input format can be anything reasonably obvious, like `>>> wangtiler 3 2`. The width and height are always positive integers.
### Example (width = 3, height = 2)
Notice that when we layout the textual tiles the neighboring edges form necessary redundant pairs of digits:
```
 1  2  1 
2 11 22 1
 2  3  2 
 2  3  2 
4 55 55 4
 1  2  2 
```
(This is NOT the proper output format.)
We can compress these horizontally and vertically to get:
```
 1 2 1 
2 1 2 1
 2 3 2 
4 5 5 4
 1 2 2 
```
This compressed format is the proper output format you must use. The odd numbered lines must include their trailing space.
# Graphical Bonus
Instead of having any textual output, your program may output an image of the tiled grid. The graphical tiles must be made up of four 45-45-90 triangles arranged in a square and use five easily distinguishable colors like the tiles above. The black borders are not required. The graphical tiles must be at least 32×32 pixels in size. No "compression" is applied to them.
**Example bonus image:** (same grid as example above)
![bonus example](https://i.stack.imgur.com/rLcIT.png)
The bonus is worth minus 150 bytes.
# Notes
* You must use this set of 13 tiles.
* Tiles may not be rotated.
* Tiles may appear any number of times (including none at all).
* You may assume a valid tiling with any dimensions is possible.
  
[Answer]
## Python (565 - 150 = 415)
Btw... it seems that we can't naively just decide the next tile by the its left and top tile. There's some combination of tiles that will fit each other.  
This solution fills in left->right, top->down brute forces through all possible combinations and backtracks if a tile cannot fit in. 
For more info about the 13 tile proof: [An aperiodic set of 13 Wang tiles](http://www.sciencedirect.com/science/article/pii/S0012365X96001185) 
Width and Height are specified by `W` and `H`
Red, Green, Blue, Yellow and Noir specified by `R`, `G`, `B`, `Y` and `N`
```
import Image,sys
W,H=map(int,sys.argv[1:])
R=99
G=R<<8
B=G<<8
Y=G+R
N=0
s="RGB";u=32;g=[[0,0]]*W*H;k=f=0
def t(c):i=Image.new(s,(2,2));k=i.load();q=16;k[1,0],k[1,1],k[0,1],k[0,0]=c;return i.resize([64]*2).rotate(45).crop((q,q,q+u,q+u))
while k<H*W:
 z=g[k][1];v=-1;j=k/W;i=k%W
 while z<13:
    l=map(eval,"GGGRRRYBGGYBGGBBRRGYYNNNNYBGBGBGRGRYRGGRRGGBBYYYYNNN"[z::13])
    if(j<1or g[(j-1)*W+i][0][2]==l[0])and(i<1or g[j*W+i-1][0][1]==l[3]):g[k]=[l,z+1];v=1;z=99
    z+=1
 g[k][1]*=(v>0);k+=v
m=Image.new(s,(W*u,H*u))
for e in g:m.paste(t(e[0]),(f%W*u,(f/W)*u));f+=1
m.show()
```
Output. Not the actual color scheme... cuz too glaring. This might make some interesting interior decor patterns...:
![enter image description here](https://i.stack.imgur.com/IVakV.png)
[Answer]
### GolfScript, 200 characters
```
~\:W*):R;1,{)\:C"=QCy_~{MTKAis]?OyJE?~WvM"[64 2400]{base}/@{>}+,{:T;[C,W<!{C W~)=T 64/^8/8%}*C,W%0>{C-1=64/T^8%}*]0-!},1<.!!{1,+}*+.,R<}do);W/.0={' '\512/8%`}%n@{.[.0=8%\{' '\64/8%}/n]\{' '\8/8%`}%n}/
```
ASCII version with no graphic output. Give the input on STDIN - try [here](http://golfscript.apphb.com/?c=OyIzIDIiCgp%2BXDpXKik6UjsxLHspXDpDIj1RQ3lffntNVEtBaXNdP095SkU%2Ffld2TSJbNjQgMjQwMF17YmFzZX0vQHs%2BfSssezpUO1tDLFc8IXtDIFd%2BKT1UIDY0L144LzglfSpDLFclMD57Qy0xPTY0L1ReOCV9Kl0wLSF9LDE8LiEhezEsK30qKy4sUjx9ZG8pO1cvLjA9eycgJ1w1MTIvOCVgfSVuQHsuWy4wPTglXHsnICdcNjQvOCV9L25dXHsnICdcOC84JWB9JW59Lw%3D%3D&run=true). The code uses a plain backtracking approach and fills the space line by line.
Examples:
```
> 3 2
 1 2 1
2 1 2 1
 2 3 2
5 4 4 5
 2 2 1
> 8 5
 1 2 1 2 1 2 1 2
2 1 2 1 2 1 2 1 2
 2 3 2 3 2 3 2 3
5 4 4 5 5 4 4 5 5
 2 2 4 2 2 2 4 2
5 4 5 5 4 5 4 4 5
 2 1 1 2 1 2 1 1
1 3 2 1 2 1 3 2 1
 2 2 2 3 2 2 2 2
5 4 5 4 4 5 4 5 4
 2 1 2 2 1 2 1 2
```
### Graphical Bonus, score 122, 272 characters - 150 bonus
```
~\:W*):R;1,{)\:C"=QCy_~{MTKAis]?OyJE?~WvM"[64 2400]{base}/@{>}+,{:T;[C,W<!{C W~)=T 64/^8/8%}*C,W%0>{C-1=64/T^8%}*]0-!},1<.!!{1,+}*+.,R<}do);W["P3\n"32W*" "3$,32*n 1n]\{{:^;512:X;16,{[^8%]1$*[^X/8%]31*@.+>[^64/8%]31*++32<}:F%8:X;16,-1%{F}%+}%zip{{+}*{8+2base(;~}%' '*n}/}/
```
Same basic code with a different output formatter. The output is an image in PPM format (i.e. simply redirect the output to a file `image.ppm`). The colors are slightly different than the tiles in the question, but clearly distinguishable (1->blue, 2->green, 3->cyan, 4->red, 5->magenta).
16x12 example:
![16x12 wang example](https://i.stack.imgur.com/fxudq.png)
[Answer]
# Haskell, 208 bytes
```
p x|x<2/3=(3!x)3"3212"3
p x=(0.5!x)1"45423"2
f=floor
(k!x)l s m=do{i<-[0,x..];[' ',s!!(2+f(i+x)-f i)]}:do{i<-[0,l*x..];s!!mod(f i)m:" "}:p(k*x)
t n=take$2*n+1
main=do(w,h)<-readLn;putStr.unlines.t h$t w<$>p 1
```
No searching, just math. Example run: given `(8,5)` on stdin, outputs
```
 2 2 2 2 2 2 2 2 
4 5 4 5 4 5 4 5 4
 1 2 1 2 1 2 1 2 
3 2 3 2 3 2 3 2 3
 2 3 2 3 2 3 2 3 
4 5 5 4 4 5 5 4 4
 4 2 2 2 4 2 2 2 
4 4 5 4 5 5 4 5 4
 1 1 2 1 1 2 1 2 
3 2 1 3 2 1 3 2 3
 2 2 2 2 2 2 2 3 
```
[Run online at Ideone](http://ideone.com/ZHZxNf)
]