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574 ihaka 1 
/*
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 *  Mathlib : A C Library of Special Functions
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 *  Copyright (C) 1998 Ross Ihaka
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 *  Copyright (C) 2000-2001 The R Development Core Team
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 *
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 *  This program is free software; you can redistribute it and/or modify
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 *  it under the terms of the GNU General Public License as published by
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 *  the Free Software Foundation; either version 2 of the License, or
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 *  (at your option) any later version.
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 *
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 *  This program is distributed in the hope that it will be useful,
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 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
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 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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 *  GNU General Public License for more details.
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 *
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 *  You should have received a copy of the GNU General Public License
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 *  along with this program; if not, write to the Free Software
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 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA.
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 *
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 *  DESCRIPTION
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 *
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 *    Pseudo-random variates from a t distribution.
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 *
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 *  NOTES
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 *
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 *    This function calls rchisq and rnorm to do the real work.
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 */
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#include "nmath.h"
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double rt(double df)
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{
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    double num;
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    if (ISNAN(df) || df <= 0.0)	ML_ERR_return_NAN;
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    if(!R_FINITE(df))
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	return norm_rand();
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    else {
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/* Some compilers (including MW6) evaluated this from right to left
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	return norm_rand() / sqrt(rchisq(df) / df); */
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	num = norm_rand();
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	return num / sqrt(rchisq(df) / df);
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    }
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}