function f = caseII( w, x ) % % evaluate the functions describing the eignenmode of case I, % a uniform string. argument w(3) is actually the eigenfrequency % c_sq = 1/( 0.001 + 0.018*x ); % **** the only line changed **** f1 = w(2); f2 = - w(1)*w(3)^2/c_sq; f3 = 0; % never change the eigenvalue --- trick! f = [ f1, f2, f3 ];