function value = von_mises_circular_variance ( a, b )

%*****************************************************************************80
%
%% von_mises_circular_variance() returns the circular variance of the von Mises PDF.
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    02 December 2004
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    real A, B, the parameters of the PDF.
%    -PI <= A <= PI,
%    0.0 < B.
%
%  Output:
%
%    real VALUE, the circular variance of the PDF.
%
  value = 1.0 - bessel_i1 ( b ) / bessel_i0 ( b );

  return
end
