www.gusucode.com > elmat工具箱matlab源码程序 > elmat/diag.m
%DIAG Diagonal matrices and diagonals of a matrix. % DIAG(V,K) when V is a vector with N components is a square matrix % of order N+ABS(K) with the elements of V on the K-th diagonal. K = 0 % is the main diagonal, K > 0 is above the main diagonal and K < 0 % is below the main diagonal. % % DIAG(V) is the same as DIAG(V,0) and puts V on the main diagonal. % % DIAG(X,K) when X is a matrix is a column vector formed from % the elements of the K-th diagonal of X. % % DIAG(X) is the main diagonal of X. DIAG(DIAG(X)) is a diagonal matrix. % % Example % m = 5; % diag(-m:m) + diag(ones(2*m,1),1) + diag(ones(2*m,1),-1) % produces a tridiagonal matrix of order 2*m+1. % % See also SPDIAGS, TRIU, TRIL, BLKDIAG. % Copyright 1984-2006 The MathWorks, Inc. % Built-in function.