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authorEric Andersen <andersen@codepoet.org>2001-11-22 14:04:29 +0000
committerEric Andersen <andersen@codepoet.org>2001-11-22 14:04:29 +0000
commit7ce331c01ce6eb7b3f5c715a38a24359da9c6ee2 (patch)
tree3a7e8476e868ae15f4da1b7ce26b2db6f434468c /libm/float/igamf.c
parentc117dd5fb183afb1a4790a6f6110d88704be6bf8 (diff)
Totally rework the math library, this time based on the MacOs X
math library (which is itself based on the math lib from FreeBSD). -Erik
Diffstat (limited to 'libm/float/igamf.c')
-rw-r--r--libm/float/igamf.c223
1 files changed, 0 insertions, 223 deletions
diff --git a/libm/float/igamf.c b/libm/float/igamf.c
deleted file mode 100644
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--- a/libm/float/igamf.c
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@@ -1,223 +0,0 @@
-/* igamf.c
- *
- * Incomplete gamma integral
- *
- *
- *
- * SYNOPSIS:
- *
- * float a, x, y, igamf();
- *
- * y = igamf( a, x );
- *
- *
- *
- * DESCRIPTION:
- *
- * The function is defined by
- *
- * x
- * -
- * 1 | | -t a-1
- * igam(a,x) = ----- | e t dt.
- * - | |
- * | (a) -
- * 0
- *
- *
- * In this implementation both arguments must be positive.
- * The integral is evaluated by either a power series or
- * continued fraction expansion, depending on the relative
- * values of a and x.
- *
- *
- *
- * ACCURACY:
- *
- * Relative error:
- * arithmetic domain # trials peak rms
- * IEEE 0,30 20000 7.8e-6 5.9e-7
- *
- */
- /* igamcf()
- *
- * Complemented incomplete gamma integral
- *
- *
- *
- * SYNOPSIS:
- *
- * float a, x, y, igamcf();
- *
- * y = igamcf( a, x );
- *
- *
- *
- * DESCRIPTION:
- *
- * The function is defined by
- *
- *
- * igamc(a,x) = 1 - igam(a,x)
- *
- * inf.
- * -
- * 1 | | -t a-1
- * = ----- | e t dt.
- * - | |
- * | (a) -
- * x
- *
- *
- * In this implementation both arguments must be positive.
- * The integral is evaluated by either a power series or
- * continued fraction expansion, depending on the relative
- * values of a and x.
- *
- *
- *
- * ACCURACY:
- *
- * Relative error:
- * arithmetic domain # trials peak rms
- * IEEE 0,30 30000 7.8e-6 5.9e-7
- *
- */
-
-/*
-Cephes Math Library Release 2.2: June, 1992
-Copyright 1985, 1987, 1992 by Stephen L. Moshier
-Direct inquiries to 30 Frost Street, Cambridge, MA 02140
-*/
-
-#include <math.h>
-
-/* BIG = 1/MACHEPF */
-#define BIG 16777216.
-
-extern float MACHEPF, MAXLOGF;
-
-#ifdef ANSIC
-float lgamf(float), expf(float), logf(float), igamf(float, float);
-#else
-float lgamf(), expf(), logf(), igamf();
-#endif
-
-#define fabsf(x) ( (x) < 0 ? -(x) : (x) )
-
-
-
-float igamcf( float aa, float xx )
-{
-float a, x, ans, c, yc, ax, y, z;
-float pk, pkm1, pkm2, qk, qkm1, qkm2;
-float r, t;
-static float big = BIG;
-
-a = aa;
-x = xx;
-if( (x <= 0) || ( a <= 0) )
- return( 1.0 );
-
-if( (x < 1.0) || (x < a) )
- return( 1.0 - igamf(a,x) );
-
-ax = a * logf(x) - x - lgamf(a);
-if( ax < -MAXLOGF )
- {
- mtherr( "igamcf", UNDERFLOW );
- return( 0.0 );
- }
-ax = expf(ax);
-
-/* continued fraction */
-y = 1.0 - a;
-z = x + y + 1.0;
-c = 0.0;
-pkm2 = 1.0;
-qkm2 = x;
-pkm1 = x + 1.0;
-qkm1 = z * x;
-ans = pkm1/qkm1;
-
-do
- {
- c += 1.0;
- y += 1.0;
- z += 2.0;
- yc = y * c;
- pk = pkm1 * z - pkm2 * yc;
- qk = qkm1 * z - qkm2 * yc;
- if( qk != 0 )
- {
- r = pk/qk;
- t = fabsf( (ans - r)/r );
- ans = r;
- }
- else
- t = 1.0;
- pkm2 = pkm1;
- pkm1 = pk;
- qkm2 = qkm1;
- qkm1 = qk;
- if( fabsf(pk) > big )
- {
- pkm2 *= MACHEPF;
- pkm1 *= MACHEPF;
- qkm2 *= MACHEPF;
- qkm1 *= MACHEPF;
- }
- }
-while( t > MACHEPF );
-
-return( ans * ax );
-}
-
-
-
-/* left tail of incomplete gamma function:
- *
- * inf. k
- * a -x - x
- * x e > ----------
- * - -
- * k=0 | (a+k+1)
- *
- */
-
-float igamf( float aa, float xx )
-{
-float a, x, ans, ax, c, r;
-
-a = aa;
-x = xx;
-if( (x <= 0) || ( a <= 0) )
- return( 0.0 );
-
-if( (x > 1.0) && (x > a ) )
- return( 1.0 - igamcf(a,x) );
-
-/* Compute x**a * exp(-x) / gamma(a) */
-ax = a * logf(x) - x - lgamf(a);
-if( ax < -MAXLOGF )
- {
- mtherr( "igamf", UNDERFLOW );
- return( 0.0 );
- }
-ax = expf(ax);
-
-/* power series */
-r = a;
-c = 1.0;
-ans = 1.0;
-
-do
- {
- r += 1.0;
- c *= x/r;
- ans += c;
- }
-while( c/ans > MACHEPF );
-
-return( ans * ax/a );
-}