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* Gamma distribution function
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* double a, b, x, y, gdtr();
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* y = gdtr( a, b, x );
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* Returns the integral from zero to x of the Gamma probability
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* The incomplete Gamma integral is used, according to the
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* message condition value returned
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* gdtr domain x < 0 0.0
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* Complemented Gamma distribution function
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* double a, b, x, y, gdtrc();
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* y = gdtrc( a, b, x );
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* Returns the integral from x to infinity of the Gamma
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* probability density function:
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* The incomplete Gamma integral is used, according to the
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* message condition value returned
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* gdtrc domain x < 0 0.0
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Cephes Math Library Release 2.3: March,1995
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Copyright 1984, 1987, 1995 by Stephen L. Moshier
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double igam(), igamc();
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double gdtri(double,double,double);
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double gdtr( a, b, x )
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mtherr( "gdtr", DOMAIN );
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return( igam( b, a * x ) );
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double gdtrc( a, b, x )
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mtherr( "gdtrc", DOMAIN );
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return( igamc( b, a * x ) );
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double gdtri( a, b, y)
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if ((y < 0.0) || (y > 1.0) || (a <= 0.0) || (b < 0.0))
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mtherr("gdtri", DOMAIN);
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return ( igami (b, 1.0-y) / a);