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authorEric Andersen <andersen@codepoet.org>2001-05-10 00:40:28 +0000
committerEric Andersen <andersen@codepoet.org>2001-05-10 00:40:28 +0000
commit1077fa4d772832f77a677ce7fb7c2d513b959e3f (patch)
tree579bee13fb0b58d2800206366ec2caecbb15f3fc /libm/double/ellik.c
parent22358dd7ce7bb49792204b698f01a6f69b9c8e08 (diff)
uClibc now has a math library. muahahahaha!
-Erik
Diffstat (limited to 'libm/double/ellik.c')
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+/* ellik.c
+ *
+ * Incomplete elliptic integral of the first kind
+ *
+ *
+ *
+ * SYNOPSIS:
+ *
+ * double phi, m, y, ellik();
+ *
+ * y = ellik( phi, m );
+ *
+ *
+ *
+ * DESCRIPTION:
+ *
+ * Approximates the integral
+ *
+ *
+ *
+ * phi
+ * -
+ * | |
+ * | dt
+ * F(phi_\m) = | ------------------
+ * | 2
+ * | | sqrt( 1 - m sin t )
+ * -
+ * 0
+ *
+ * of amplitude phi and modulus m, using the arithmetic -
+ * geometric mean algorithm.
+ *
+ *
+ *
+ *
+ * ACCURACY:
+ *
+ * Tested at random points with m in [0, 1] and phi as indicated.
+ *
+ * Relative error:
+ * arithmetic domain # trials peak rms
+ * IEEE -10,10 200000 7.4e-16 1.0e-16
+ *
+ *
+ */
+
+
+/*
+Cephes Math Library Release 2.8: June, 2000
+Copyright 1984, 1987, 2000 by Stephen L. Moshier
+*/
+
+/* Incomplete elliptic integral of first kind */
+
+#include <math.h>
+#ifdef ANSIPROT
+extern double sqrt ( double );
+extern double fabs ( double );
+extern double log ( double );
+extern double tan ( double );
+extern double atan ( double );
+extern double floor ( double );
+extern double ellpk ( double );
+double ellik ( double, double );
+#else
+double sqrt(), fabs(), log(), tan(), atan(), floor(), ellpk();
+double ellik();
+#endif
+extern double PI, PIO2, MACHEP, MAXNUM;
+
+double ellik( phi, m )
+double phi, m;
+{
+double a, b, c, e, temp, t, K;
+int d, mod, sign, npio2;
+
+if( m == 0.0 )
+ return( phi );
+a = 1.0 - m;
+if( a == 0.0 )
+ {
+ if( fabs(phi) >= PIO2 )
+ {
+ mtherr( "ellik", SING );
+ return( MAXNUM );
+ }
+ return( log( tan( (PIO2 + phi)/2.0 ) ) );
+ }
+npio2 = floor( phi/PIO2 );
+if( npio2 & 1 )
+ npio2 += 1;
+if( npio2 )
+ {
+ K = ellpk( a );
+ phi = phi - npio2 * PIO2;
+ }
+else
+ K = 0.0;
+if( phi < 0.0 )
+ {
+ phi = -phi;
+ sign = -1;
+ }
+else
+ sign = 0;
+b = sqrt(a);
+t = tan( phi );
+if( fabs(t) > 10.0 )
+ {
+ /* Transform the amplitude */
+ e = 1.0/(b*t);
+ /* ... but avoid multiple recursions. */
+ if( fabs(e) < 10.0 )
+ {
+ e = atan(e);
+ if( npio2 == 0 )
+ K = ellpk( a );
+ temp = K - ellik( e, m );
+ goto done;
+ }
+ }
+a = 1.0;
+c = sqrt(m);
+d = 1;
+mod = 0;
+
+while( fabs(c/a) > MACHEP )
+ {
+ temp = b/a;
+ phi = phi + atan(t*temp) + mod * PI;
+ mod = (phi + PIO2)/PI;
+ t = t * ( 1.0 + temp )/( 1.0 - temp * t * t );
+ c = ( a - b )/2.0;
+ temp = sqrt( a * b );
+ a = ( a + b )/2.0;
+ b = temp;
+ d += d;
+ }
+
+temp = (atan(t) + mod * PI)/(d * a);
+
+done:
+if( sign < 0 )
+ temp = -temp;
+temp += npio2 * K;
+return( temp );
+}