function variance = student_variance ( a, b, c ) %*****************************************************************************80 % %% STUDENT_VARIANCE returns the variance of the central Student T PDF. % % Discussion: % % For the variance to exist, it is necessary that 2 < C. % % Licensing: % % This code is distributed under the GNU LGPL license. % % Modified: % % 02 November 2005 % % Author: % % John Burkardt % % Parameters: % % Input, real A, B, shape parameters of the PDF, % used to transform the argument X to a shifted and scaled % value Y = ( X - A ) / B. It is required that B be nonzero. % For the standard distribution, A = 0 and B = 1. % % Input, real C, is usually called the number of % degrees of freedom of the distribution. C is typically an % integer, but that is not essential. It is required that % C be strictly positive. % % Output, real VARIANCE, the variance of the PDF. % if ( c <= 2.0 ) fprintf ( 1, '\n' ); fprintf ( 1, 'STUDENT_VARIANCE - Fatal error!\n' ); fprintf ( 1, ' Variance not defined for C <= 2.\n' ); error ( 'STUDENT_VARIANCE - Fatal error!' ); end variance = b * b * c / ( c - 2.0 ); return end