%row reduction algorithm%
A=[0,-3,-6,4,9;-3,-5,-1,6,0;-1,1,5,-6,-8;1,4,5,-9,-7]
A=i(A,1,4)
A=r(A,3,1,2)
A=r(A,1,1,3)
A=s(A,2,1/7)
A=r(A,-5,2,3)
A=r(A,3,2,4)
A=i(A,3,4)