Pivot[A_,k_,l_]:=Module[{B=A},
m=Dimensions[A][[1]];n=Dimensions[A][[2]];
For[i=1,i<=m,i++,
If[i==k,
B[[i]]=A[[i]]/A[[k,l]],
   B[[i]]=-A[[i,l]]/A[[k,l]]*A[[k]]+A[[i]]]
];
B
]