function value = r8_modp ( x, y )
%*****************************************************************************80
%
%% R8_MODP returns the nonnegative remainder of real division.
%
% Discussion:
%
% If
% REM = R8_MODP ( X, Y )
% RMULT = ( X - REM ) / Y
% then
% X = Y * RMULT + REM
% where REM is always nonnegative.
%
% The MOD function computes a result with the same sign as the
% quantity being divided. Thus, suppose you had an angle A,
% and you wanted to ensure that it was between 0 and 360.
% Then mod(A,360.0) would do, if A was positive, but if A
% was negative, your result would be between -360 and 0.
%
% On the other hand, R8_MODP(A,360.0) is between 0 and 360, always.
%
% Example:
%
% I J MOD R8_MODP R8_MODP Factorization
%
% 107 50 7 7 107 = 2 * 50 + 7
% 107 -50 7 7 107 = -2 * -50 + 7
% -107 50 -7 43 -107 = -3 * 50 + 43
% -107 -50 -7 43 -107 = 3 * -50 + 43
%
% Licensing:
%
% This code is distributed under the GNU LGPL license.
%
% Modified:
%
% 09 January 2005
%
% Author:
%
% John Burkardt
%
% Input:
%
% real X, the number to be divided.
%
% real Y, the number that divides X.
%
% Output:
%
% real VALUE, the nonnegative remainder when X is divided by Y.
%
if ( y == 0.0 )
fprintf ( 1, '\n' );
fprintf ( 1, 'R8_MODP - Fatal error!\n' );
fprintf ( 1, ' R8_MODP ( X, Y ) called with Y = %f\n', y );
error ( 'R8_MODP - Fatal error!' );
end
value = mod ( x, y );
if ( value < 0.0 )
value = value + abs ( y );
end
return
end