Number 1

Read a matrix, for example:

  4 4
     1 0 1 -1
     1 -1 0 6
     1 0 -1 7
     1 1 0 -2

This is a matrix for the following inequalities:

     1 = inequality,  0x +  1y -1 >=0  -->	y >= 1
     1 = inequality, -1x +  0y +6 >=0  -->	x <= 6
     1 = inequality,  0x + -1y +7 >=0  -->	y <= 7
     1 = inequality,  1x +  0y -2 >=0  -->	x >= 2

Notice that if the first number was a 0 instead of a 1, then that constraint would be an equality instead of an inequality.