B1=transpose([1,5,-1 ;4,1,1;2,-2,1])
B2=transpose([2,3,0 ;1,1,0; 3,0,1])
xb1=transpose([1,0,-1])
b2min1=inv(B2)
xb2=b2min1*B1*xb1
b1dual=transpose(inv(B1))
si=transpose([1,2,3])
sib1=b1dual*si