www.gusucode.com > 矩阵计算工具箱 - mctoolbox源码程序 > matrixcomp\sub.m
function S = sub(A, i, j) %SUB Principal submatrix. % SUB(A,i,j) is A(i:j,i:j). % SUB(A,i) is the leading principal submatrix of order i, % A(1:i,1:i), if i>0, and the trailing principal submatrix % of order ABS(i) if i<0. if nargin == 2 if i >= 0 S = A(1:i, 1:i); else n = min(size(A)); S = A(n+i+1:n, n+i+1:n); end else S = A(i:j, i:j); end