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+/* gdtr.c
+ *
+ * Gamma distribution function
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * double a, b, x, y, gdtr();
+ *
+ * y = gdtr( a, b, x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns the integral from zero to x of the gamma probability
+ * density function:
+ *
+ *
+ * x
+ * b -
+ * a | | b-1 -at
+ * y = ----- | t e dt
+ * - | |
+ * | (b) -
+ * 0
+ *
+ * The incomplete gamma integral is used, according to the
+ * relation
+ *
+ * y = igam( b, ax ).
+ *
+ *
+ * ACCURACY:
+ *
+ * See igam().
+ *
+ * ERROR MESSAGES:
+ *
+ * message condition value returned
+ * gdtr domain x < 0 0.0
+ *
+ */
+ /* gdtrc.c
+ *
+ * Complemented gamma distribution function
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * double a, b, x, y, gdtrc();
+ *
+ * y = gdtrc( a, b, x );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Returns the integral from x to infinity of the gamma
+ * probability density function:
+ *
+ *
+ * inf.
+ * b -
+ * a | | b-1 -at
+ * y = ----- | t e dt
+ * - | |
+ * | (b) -
+ * x
+ *
+ * The incomplete gamma integral is used, according to the
+ * relation
+ *
+ * y = igamc( b, ax ).
+ *
+ *
+ * ACCURACY:
+ *
+ * See igamc().
+ *
+ * ERROR MESSAGES:
+ *
+ * message condition value returned
+ * gdtrc domain x < 0 0.0
+ *
+ */
+
+/* gdtr() */
+
+
+/*
+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 );
+#else
+double igam(), igamc();
+#endif
+
+double gdtr( a, b, x )
+double a, b, x;
+{
+
+if( x < 0.0 )
+ {
+ mtherr( "gdtr", DOMAIN );
+ return( 0.0 );
+ }
+return( igam( b, a * x ) );
+}
+
+
+
+double gdtrc( a, b, x )
+double a, b, x;
+{
+
+if( x < 0.0 )
+ {
+ mtherr( "gdtrc", DOMAIN );
+ return( 0.0 );
+ }
+return( igamc( b, a * x ) );
+}