Using matlab to create a list of y=x1 x2 ... 
  for all possible combinations of x variables.

  k = number of variables (unlimited number of variables)

Look in temp.txt for results.  The diary command will APPEND to temp.txt.

Start matlab and run the following code:

=== BEGIN ===
diary('temp.txt');
k=4;
n=2^k-1;
b=zeros(1,k);
for i=1:n;
 temp=i;
 for j=1:k;
  b(1,j)=mod(temp,2);
  temp=temp-b(1,j);
  temp=temp/2;
 end;
 fprintf(1,'y =');
 for j=1:k;
  if b(1,j) == 1;
   fprintf(1,' x%u',j);
  end;
 end;
 fprintf(1,'\n');
end;
diary('off');
==== END ====