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 *
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 *
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 *    The t density is evaluated as
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 *    The t density is evaluated as
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 *         sqrt(n/2) / ((n+1)/2) * Gamma((n+3)/2) / Gamma((n+2)/2).
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 *         sqrt(n/2) / ((n+1)/2) * Gamma((n+3)/2) / Gamma((n+2)/2).
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 *             * (1+x^2/n)^(-n/2)
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 *             * (1+x^2/n)^(-n/2)
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 *             / sqrt( 2 pi (1+x^2/n) )
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 *             / sqrt( 2 pi (1+x^2/n) )
- 
 
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 *
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 *    This form leads to a stable computation for all
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 *    This form leads to a stable computation for all
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 *    values of n, including n -> 0 and n -> infinity.
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 *    values of n, including n -> 0 and n -> infinity.
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 *
 - 
 
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 */
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 */
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#include "nmath.h"
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#include "nmath.h"
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#include "dpq.h"
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#include "dpq.h"
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double dt(double x, double n, int give_log)
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double dt(double x, double n, int give_log)
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{
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{
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    double t, u;
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    double t, u;
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#ifdef IEEE_754
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#ifdef IEEE_754
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    if (ISNAN(x) || ISNAN(n))
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    if (ISNAN(x) || ISNAN(n))
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	return x + n;
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	return x + n;
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#endif
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#endif