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-/* ellpjf.c
- *
- * Jacobian Elliptic Functions
- *
- *
- *
- * SYNOPSIS:
- *
- * float u, m, sn, cn, dn, phi;
- * int ellpj();
- *
- * ellpj( u, m, _&sn, _&cn, _&dn, _&phi );
- *
- *
- *
- * DESCRIPTION:
- *
- *
- * Evaluates the Jacobian elliptic functions sn(u|m), cn(u|m),
- * and dn(u|m) of parameter m between 0 and 1, and real
- * argument u.
- *
- * These functions are periodic, with quarter-period on the
- * real axis equal to the complete elliptic integral
- * ellpk(1.0-m).
- *
- * Relation to incomplete elliptic integral:
- * If u = ellik(phi,m), then sn(u|m) = sin(phi),
- * and cn(u|m) = cos(phi). Phi is called the amplitude of u.
- *
- * Computation is by means of the arithmetic-geometric mean
- * algorithm, except when m is within 1e-9 of 0 or 1. In the
- * latter case with m close to 1, the approximation applies
- * only for phi < pi/2.
- *
- * ACCURACY:
- *
- * Tested at random points with u between 0 and 10, m between
- * 0 and 1.
- *
- * Absolute error (* = relative error):
- * arithmetic function # trials peak rms
- * IEEE sn 10000 1.7e-6 2.2e-7
- * IEEE cn 10000 1.6e-6 2.2e-7
- * IEEE dn 10000 1.4e-3 1.9e-5
- * IEEE phi 10000 3.9e-7* 6.7e-8*
- *
- * Peak error observed in consistency check using addition
- * theorem for sn(u+v) was 4e-16 (absolute). Also tested by
- * the above relation to the incomplete elliptic integral.
- * Accuracy deteriorates when u is large.
- *
- */
-
-/* ellpj.c */
-
-
-/*
-Cephes Math Library Release 2.2: July, 1992
-Copyright 1984, 1987, 1992 by Stephen L. Moshier
-Direct inquiries to 30 Frost Street, Cambridge, MA 02140
-*/
-
-#include <math.h>
-extern float PIO2F, MACHEPF;
-
-#define fabsf(x) ( (x) < 0 ? -(x) : (x) )
-
-#ifdef ANSIC
-float sqrtf(float), sinf(float), cosf(float), asinf(float), tanhf(float);
-float sinhf(float), coshf(float), atanf(float), expf(float);
-#else
-float sqrtf(), sinf(), cosf(), asinf(), tanhf();
-float sinhf(), coshf(), atanf(), expf();
-#endif
-
-int ellpjf( float uu, float mm,
- float *sn, float *cn, float *dn, float *ph )
-{
-float u, m, ai, b, phi, t, twon;
-float a[10], c[10];
-int i;
-
-u = uu;
-m = mm;
-/* Check for special cases */
-
-if( m < 0.0 || m > 1.0 )
- {
- mtherr( "ellpjf", DOMAIN );
- return(-1);
- }
-if( m < 1.0e-5 )
- {
- t = sinf(u);
- b = cosf(u);
- ai = 0.25 * m * (u - t*b);
- *sn = t - ai*b;
- *cn = b + ai*t;
- *ph = u - ai;
- *dn = 1.0 - 0.5*m*t*t;
- return(0);
- }
-
-if( m >= 0.99999 )
- {
- ai = 0.25 * (1.0-m);
- b = coshf(u);
- t = tanhf(u);
- phi = 1.0/b;
- twon = b * sinhf(u);
- *sn = t + ai * (twon - u)/(b*b);
- *ph = 2.0*atanf(expf(u)) - PIO2F + ai*(twon - u)/b;
- ai *= t * phi;
- *cn = phi - ai * (twon - u);
- *dn = phi + ai * (twon + u);
- return(0);
- }
-
-
-/* A. G. M. scale */
-a[0] = 1.0;
-b = sqrtf(1.0 - m);
-c[0] = sqrtf(m);
-twon = 1.0;
-i = 0;
-
-while( fabsf( (c[i]/a[i]) ) > MACHEPF )
- {
- if( i > 8 )
- {
-/* mtherr( "ellpjf", OVERFLOW );*/
- break;
- }
- ai = a[i];
- ++i;
- c[i] = 0.5 * ( ai - b );
- t = sqrtf( ai * b );
- a[i] = 0.5 * ( ai + b );
- b = t;
- twon += twon;
- }
-
-
-/* backward recurrence */
-phi = twon * a[i] * u;
-do
- {
- t = c[i] * sinf(phi) / a[i];
- b = phi;
- phi = 0.5 * (asinf(t) + phi);
- }
-while( --i );
-
-*sn = sinf(phi);
-t = cosf(phi);
-*cn = t;
-*dn = t/cosf(phi-b);
-*ph = phi;
-return(0);
-}