function [ n_data_new, x, fx ] = psi_values ( n_data ) %*****************************************************************************80 % %% PSI_VALUES returns some values of the Psi or Digamma function. % % Discussion: % % PSI(X) = d LN ( GAMMA ( X ) ) / d X = GAMMA'(X) / GAMMA(X) % % PSI(1) = - Euler's constant. % % PSI(X+1) = PSI(X) + 1 / X. % % Licensing: % % This code is distributed under the GNU LGPL license. % % Modified: % % 26 May 2004 % % Author: % % John Burkardt % % Reference: % % Milton Abramowitz and Irene Stegun, % Handbook of Mathematical Functions, % US Department of Commerce, 1964. % % Parameters: % % Input, integer N_DATA, indicates the index of the previous test data % returned, or is 0 if this is the first call. For repeated calls, % set the input value of N_DATA to the output value of N_DATA_NEW % from the previous call. % % Output, integer N_DATA_NEW, the index of the test data. % % Output, real X, the argument of the function. % % Output, real FX, the value of the function. % n_max = 11; fx_vec = [ ... -0.5772156649E+00, -0.4237549404E+00, -0.2890398966E+00, ... -0.1691908889E+00, -0.0613845446E+00, -0.0364899740E+00, ... 0.1260474528E+00, 0.2085478749E+00, 0.2849914333E+00, ... 0.3561841612E+00, 0.4227843351E+00 ]; x_vec = [ ... 1.0E+00, 1.1E+00, 1.2E+00, ... 1.3E+00, 1.4E+00, 1.5E+00, ... 1.6E+00, 1.7E+00, 1.8E+00, ... 1.9E+00, 2.0E+00 ]; n_data_new = n_data; if ( n_data_new < 0 ) n_data_new = 0; end n_data_new = n_data_new + 1; if ( n_max < n_data_new ) n_data_new = 0; x = 0.0E+00; fx = 0.0E+00; else x = x_vec(n_data_new); fx = fx_vec(n_data_new); end return end