Prime Number Matrix: Something Unexpected

After spending some time thinking about what most would consider "unrelated" to this subject, i.e. the necessary figure/ground basis of consciousness, I decided to switch gears and play around with GNU Octave. After about an hour, I came up with this code. What it basically does is take all the possible sums of prime numbers in the interval [2,arg1]. The program computes all possible sums of this prime vector with itself and puts them into a matrix. It then assigns a '1' or '0' depending on the result being what I called "singular even" or "composite even." Definitions are further explained in the comment block. The resulting '1s and 0s' matrix is then rasterized, producing the image below (be sure to check it in the thumbnails strip).

##
## visprimes
## Yet another visualization scheme for prime numbers
## Internal Variables:
## arg1 - maximum order (primes up to "arg1")
## arg2 - return type "raw" or "bin":
##              "raw" gives a matrix of all possible sums of the primes in pvec
##              "bin" returns a 1 or 0 depending on the type of even number returned
##              according to the following definitions:
##                      Singular Even <=> arg/2 is prime
##                      Composite Even <=> arg/2 is composite
## USAGE: [] = visprimes(arg1,arg2)
## Author: AllenMi

Created: 2009-3-11

function [ a ] = visprimes (arg1,arg2)

   more off ## turns off the output supression
   printf("Loading the prime vector...\n")
   pvec = primes(arg1);
   printf("Finished...\n")
   printf("Obtaining dimensions of prime vector...\n")
   pvecSize = size(pvec)(2);
   printf("Finished...\n")
   flag = 0; ## Flag for graphing if bin only
   ## Case for raw
   if (arg2 == "raw")
      flag = 1
      for i=1:pvecSize
         if (mod(i,20) == 0)
           printf("Progress is %d%%.\n",i/pvecSize*100)
         endif
         for j=1:pvecSize
            a(i,j) = pvec(i)+pvec(j);
         endfor
      endfor
     ## Case for bin
     elseif(arg2 == "bin")
        for i=1:pvecSize
           if (mod(i,20) == 0)
              printf("Progress is %d%%.\n",i/pvecSize*100)
           endif
           for j=1:pvecSize
              a(i,j) = isprime((pvec(i)+pvec(j))/2);
           endfor
         endfor
      endif
## Case for bin-ng

## Graphing output
newplot();
if(flag == 0)
printf("Setting colormap...\n")
colormap(bone(64)); ## sets colormap to black and white
printf("Create image...\n")
image(gray2ind(a));
printf("Done!\n")
else
printf("Cancelling graphics...\n")
endif
more on ##turns back on the output supression
endfunction