1 files changed, 184 insertions, 0 deletions
diff --git a/libm/double/pdtr.c b/libm/double/pdtr.c
new file mode 100644
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+/*							pdtr.c
+ *
+ *	Poisson distribution
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * int k;
+ * double m, y, pdtr();
+ *
+ * y = pdtr( k, m );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns the sum of the first k terms of the Poisson
+ * distribution:
+ *
+ *   k         j
+ *   --   -m  m
+ *   >   e    --
+ *   --       j!
+ *  j=0
+ *
+ * The terms are not summed directly; instead the incomplete
+ * gamma integral is employed, according to the relation
+ *
+ * y = pdtr( k, m ) = igamc( k+1, m ).
+ *
+ * The arguments must both be positive.
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ * See igamc().
+ *
+ */
+/*							pdtrc()
+ *
+ *	Complemented poisson distribution
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * int k;
+ * double m, y, pdtrc();
+ *
+ * y = pdtrc( k, m );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns the sum of the terms k+1 to infinity of the Poisson
+ * distribution:
+ *
+ *  inf.       j
+ *   --   -m  m
+ *   >   e    --
+ *   --       j!
+ *  j=k+1
+ *
+ * The terms are not summed directly; instead the incomplete
+ * gamma integral is employed, according to the formula
+ *
+ * y = pdtrc( k, m ) = igam( k+1, m ).
+ *
+ * The arguments must both be positive.
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ * See igam.c.
+ *
+ */
+/*							pdtri()
+ *
+ *	Inverse Poisson distribution
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * int k;
+ * double m, y, pdtr();
+ *
+ * m = pdtri( k, y );
+ *
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Finds the Poisson variable x such that the integral
+ * from 0 to x of the Poisson density is equal to the
+ * given probability y.
+ *
+ * This is accomplished using the inverse gamma integral
+ * function and the relation
+ *
+ *    m = igami( k+1, y ).
+ *
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ * See igami.c.
+ *
+ * ERROR MESSAGES:
+ *
+ *   message         condition      value returned
+ * pdtri domain    y < 0 or y >= 1       0.0
+ *                     k < 0
+ *
+ */
+
+/*
+Cephes Math Library Release 2.8:  June, 2000
+Copyright 1984, 1987, 1995, 2000 by Stephen L. Moshier
+*/
+
+#include <math.h>
+#ifdef ANSIPROT
+extern double igam ( double, double );
+extern double igamc ( double, double );
+extern double igami ( double, double );
+#else
+double igam(), igamc(), igami();
+#endif
+
+double pdtrc( k, m )
+int k;
+double m;
+{
+double v;
+
+if( (k < 0) || (m <= 0.0) )
+	{
+	mtherr( "pdtrc", DOMAIN );
+	return( 0.0 );
+	}
+v = k+1;
+return( igam( v, m ) );
+}
+
+
+
+double pdtr( k, m )
+int k;
+double m;
+{
+double v;
+
+if( (k < 0) || (m <= 0.0) )
+	{
+	mtherr( "pdtr", DOMAIN );
+	return( 0.0 );
+	}
+v = k+1;
+return( igamc( v, m ) );
+}
+
+
+double pdtri( k, y )
+int k;
+double y;
+{
+double v;
+
+if( (k < 0) || (y < 0.0) || (y >= 1.0) )
+	{
+	mtherr( "pdtri", DOMAIN );
+	return( 0.0 );
+	}
+v = k+1;
+v = igami( v, y );
+return( v );
+}