int gsl_sf_hyperg_2F1_renorm_e(const double a, const double b, const double c, const double x, gsl_sf_result * result ) { const double rinta = floor(a + 0.5); const double rintb = floor(b + 0.5); const double rintc = floor(c + 0.5); const int a_neg_integer = ( a < 0.0 && fabs(a - rinta) < locEPS ); const int b_neg_integer = ( b < 0.0 && fabs(b - rintb) < locEPS ); const int c_neg_integer = ( c < 0.0 && fabs(c - rintc) < locEPS ); if(c_neg_integer) { if((a_neg_integer && a > c+0.1) || (b_neg_integer && b > c+0.1)) { /* 2F1 terminates early */ result->val = 0.0; result->err = 0.0; return GSL_SUCCESS; } else { /* 2F1 does not terminate early enough, so something survives */ /* [Abramowitz+Stegun, 15.1.2] */ gsl_sf_result g1, g2, g3, g4, g5; double s1, s2, s3, s4, s5; int stat = 0; stat += gsl_sf_lngamma_sgn_e(a-c+1, &g1, &s1); stat += gsl_sf_lngamma_sgn_e(b-c+1, &g2, &s2); stat += gsl_sf_lngamma_sgn_e(a, &g3, &s3); stat += gsl_sf_lngamma_sgn_e(b, &g4, &s4); stat += gsl_sf_lngamma_sgn_e(-c+2, &g5, &s5); if(stat != 0) { DOMAIN_ERROR(result); } else { gsl_sf_result F; int stat_F = gsl_sf_hyperg_2F1_e(a-c+1, b-c+1, -c+2, x, &F); double ln_pre_val = g1.val + g2.val - g3.val - g4.val - g5.val; double ln_pre_err = g1.err + g2.err + g3.err + g4.err + g5.err; double sg = s1 * s2 * s3 * s4 * s5; int stat_e = gsl_sf_exp_mult_err_e(ln_pre_val, ln_pre_err, sg * F.val, F.err, result); return GSL_ERROR_SELECT_2(stat_e, stat_F); } } } else { /* generic c */ gsl_sf_result F; gsl_sf_result lng; double sgn; int stat_g = gsl_sf_lngamma_sgn_e(c, &lng, &sgn); int stat_F = gsl_sf_hyperg_2F1_e(a, b, c, x, &F); int stat_e = gsl_sf_exp_mult_err_e(-lng.val, lng.err, sgn*F.val, F.err, result); return GSL_ERROR_SELECT_3(stat_e, stat_F, stat_g); } }
/// Hypergeometric functions. double hyperg(double a, double b, double c, double x) { gsl_sf_result result; int stat = gsl_sf_hyperg_2F1_e(a, b, c, x, &result); if (stat != GSL_SUCCESS) { std::ostringstream msg("Error in hyperg:"); msg << " a=" << a << " b=" << b << " c=" << c << " x=" << x; throw std::runtime_error(msg.str()); } else return result.val; }
int gsl_sf_beta_inc_e( const double a, const double b, const double x, gsl_sf_result * result ) { if(x < 0.0 || x > 1.0) { DOMAIN_ERROR(result); } else if (isnegint(a) || isnegint(b)) { DOMAIN_ERROR(result); } else if (isnegint(a+b)) { DOMAIN_ERROR(result); } else if(x == 0.0) { result->val = 0.0; result->err = 0.0; return GSL_SUCCESS; } else if(x == 1.0) { result->val = 1.0; result->err = 0.0; return GSL_SUCCESS; } else if (a <= 0 || b <= 0) { gsl_sf_result f, beta; int stat; const int stat_f = gsl_sf_hyperg_2F1_e(a, 1-b, a+1, x, &f); const int stat_beta = gsl_sf_beta_e(a, b, &beta); double prefactor = (pow(x, a) / a); result->val = prefactor * f.val / beta.val; result->err = fabs(prefactor) * f.err/ fabs(beta.val) + fabs(result->val/beta.val) * beta.err; stat = GSL_ERROR_SELECT_2(stat_f, stat_beta); if(stat == GSL_SUCCESS) { CHECK_UNDERFLOW(result); } return stat; } else { gsl_sf_result ln_beta; gsl_sf_result ln_x; gsl_sf_result ln_1mx; gsl_sf_result prefactor; const int stat_ln_beta = gsl_sf_lnbeta_e(a, b, &ln_beta); const int stat_ln_1mx = gsl_sf_log_1plusx_e(-x, &ln_1mx); const int stat_ln_x = gsl_sf_log_e(x, &ln_x); const int stat_ln = GSL_ERROR_SELECT_3(stat_ln_beta, stat_ln_1mx, stat_ln_x); const double ln_pre_val = -ln_beta.val + a * ln_x.val + b * ln_1mx.val; const double ln_pre_err = ln_beta.err + fabs(a*ln_x.err) + fabs(b*ln_1mx.err); const int stat_exp = gsl_sf_exp_err_e(ln_pre_val, ln_pre_err, &prefactor); if(stat_ln != GSL_SUCCESS) { result->val = 0.0; result->err = 0.0; GSL_ERROR ("error", GSL_ESANITY); } if(x < (a + 1.0)/(a+b+2.0)) { /* Apply continued fraction directly. */ gsl_sf_result cf; const int stat_cf = beta_cont_frac(a, b, x, &cf); int stat; result->val = prefactor.val * cf.val / a; result->err = (fabs(prefactor.err * cf.val) + fabs(prefactor.val * cf.err))/a; stat = GSL_ERROR_SELECT_2(stat_exp, stat_cf); if(stat == GSL_SUCCESS) { CHECK_UNDERFLOW(result); } return stat; } else { /* Apply continued fraction after hypergeometric transformation. */ gsl_sf_result cf; const int stat_cf = beta_cont_frac(b, a, 1.0-x, &cf); int stat; const double term = prefactor.val * cf.val / b; result->val = 1.0 - term; result->err = fabs(prefactor.err * cf.val)/b; result->err += fabs(prefactor.val * cf.err)/b; result->err += 2.0 * GSL_DBL_EPSILON * (1.0 + fabs(term)); stat = GSL_ERROR_SELECT_2(stat_exp, stat_cf); if(stat == GSL_SUCCESS) { CHECK_UNDERFLOW(result); } return stat; } } }
double gsl_sf_hyperg_2F1(double a, double b, double c, double x) { EVAL_RESULT(gsl_sf_hyperg_2F1_e(a, b, c, x, &result)); }