c = [ -1 -1 0 0 0 0 0 ]' ;
b = [ 7 40 50 9 70 ]' ;
A = [-1   1   1  0  0  0  0
      1   4   0  1  0  0  0
      3   2   0  0  1  0  0
      1  -3   0  0  0  1  0  
      7  -4   0  0  0  0  1 ];
bix = [3 4 5 6 7];
zcheat = -19; 
xcheat = [12 7 12 0 0 18 14]';

