load('can_256') who Your variables are: Problem Problem Problem = title: '1SYMMETRIC PATTERN FROM CANNES,LUCIEN MARRO,JUNE 1981. ' A: [256x256 double] name: 'HB/can_256' A = Problem.A; spy(A) p = bfs(A,1); B = A(p,p); spy(B) [L U] = lu(A); nnz(L+U) ans = 30811 [L U] = lu(B); nnz(L+U) ans = 25426 p = cmk1(A,1); C = A(p,p); [L U] = lu(C); nnz(L+U) ans = 19692 nnz(A) ans = 2916 p = p (end:-1:1); C = A(p,p); [L U] = lu(C); nnz(L+U) ans = 11773 p = cmk1(A,1); C = A(p,p); spy(C) p = p (end:-1:1); C = A(p,p); spy(C) p = symrcm(A); C = A(p,p); [L U] = lu(C); nnz(L+U) ans = 10934 p(end) ans = 255 p = cmk1(A,255); p = p(end:-1:1); C = A(p,p); nnz(L+U) ans = 10934 [L U] = lu(C); nnz(L+U) ans = 10934 p = symamd(A); C = A(p,p); [L U] = lu(C); nnz(L+U) ans = 7521 diary off