function [ a, q, lambda, seed ] = r8symm_test ( n, lambda_mean, lambda_dev, ... seed ) %*****************************************************************************80 % %% R8SYMM_TEST determines a symmetric matrix with a certain eigenstructure. % % Discussion: % % An R8SYMM is a real symmetric matrix stored using full storage, and % using R8 arithmetic. % % Licensing: % % This code is distributed under the GNU LGPL license. % % Modified: % % 21 February 2012 % % Author: % % John Burkardt % % Parameters: % % Input, integer N, the order of the matrix. % % Input, real LAMBDA_MEAN, the mean value of the normal % distribution from which the eigenvalues will be chosen. % % Input, real LAMBDA_DEV, the standard deviation of the normal % distribution from which the eigenvalues will be chosen. % % Input/output, integer SEED, a seed for the random % number generator. % % Output, real A(N,N), the test matrix. % % Output, real Q(N,N), the eigenvector matrix. % % Output, real LAMBDA(N), the eigenvalue vector. % % % Choose the eigenvalues LAMBDA. % [ lambda, seed ] = r8vec_normal ( n, lambda_mean, lambda_dev, seed ); % % Get a random orthogonal matrix Q. % [ q, seed ] = r8mat_orth_uniform ( n, seed ); % % Set A = Q * Lambda*I * Q'. % a = q * diag ( lambda ) * q'; return end