function x = fisk_cdf_inv ( cdf, a, b, c )

%*****************************************************************************80
%
%% fisk_cdf_inv() inverts the Fisk CDF.
%
%  Licensing:
%
%    This code is distributed under the MIT license.
%
%  Modified:
%
%    12 January 2021
%
%  Author:
%
%    John Burkardt
%
%  Input:
%
%    real CDF, the value of the CDF.
%    0.0 <= CDF <= 1.0.
%
%    real A, B, C, the parameters of the PDF.
%    0.0 < B,
%    0.0 < C.
%
%  Output:
%
%    real X, the corresponding argument of the CDF.
%
  if ( cdf < 0.0 | 1.0 < cdf )
    fprintf ( 1, '\n' );
    fprintf ( 1, 'FISK_CDF_INV - Fatal error!\n' );
    fprintf ( 1, '  CDF < 0 or 1 < CDF.\n' );
    error ( 'FISK_CDF_INV - Fatal error!' );
  end

  if ( cdf <= 0.0 )
    x = a;
  elseif ( cdf < 1.0 )
    x = a + b * ( cdf / ( 1.0 - cdf ) )^( 1.0 / c );
  elseif ( 1.0 <= cdf )
    x = Inf;
  end

  return
end
