function f = caseI( w, x ) % % evaluate the functions describing the eignenmode of case I, % a uniform string. argument w(3) is actually the eigenfrequency % c_sq = 100.0; % the square of the wave speed, c^2 f1 = w(2); f2 = - w(1)*w(3)^2/c_sq; f3 = 0; % never change the eigenvalue --- trick! f = [ f1, f2, f3 ];