int gsl_sf_bessel_I1_e(const double x, gsl_sf_result * result) { const double xmin = 2.0 * GSL_DBL_MIN; const double x_small = ROOT_EIGHT * GSL_SQRT_DBL_EPSILON; const double y = fabs(x); /* CHECK_POINTER(result) */ if(y == 0.0) { result->val = 0.0; result->err = 0.0; return GSL_SUCCESS; } else if(y < xmin) { UNDERFLOW_ERROR(result); } else if(y < x_small) { result->val = 0.5*x; result->err = 0.0; return GSL_SUCCESS; } else if(y <= 3.0) { gsl_sf_result c; cheb_eval_e(&bi1_cs, y*y/4.5-1.0, &c); result->val = x * (0.875 + c.val); result->err = y * c.err; result->err += 2.0 * GSL_DBL_EPSILON * fabs(result->val); return GSL_SUCCESS; } else if(y < GSL_LOG_DBL_MAX) { const double ey = exp(y); gsl_sf_result I1_scaled; gsl_sf_bessel_I1_scaled_e(x, &I1_scaled); result->val = ey * I1_scaled.val; result->err = ey * I1_scaled.err + y * GSL_DBL_EPSILON * fabs(result->val); result->err += 2.0 * GSL_DBL_EPSILON * fabs(result->val); return GSL_SUCCESS; } else { OVERFLOW_ERROR(result); } }
int gsl_sf_bessel_In_scaled_e(int n, const double x, gsl_sf_result * result) { const double ax = fabs(x); n = abs(n); /* I(-n, z) = I(n, z) */ /* CHECK_POINTER(result) */ if(n == 0) { return gsl_sf_bessel_I0_scaled_e(x, result); } else if(n == 1) { return gsl_sf_bessel_I1_scaled_e(x, result); } else if(x == 0.0) { result->val = 0.0; result->err = 0.0; return GSL_SUCCESS; } else if(x*x < 10.0*(n+1.0)/M_E) { gsl_sf_result t; double ex = exp(-ax); int stat_In = gsl_sf_bessel_IJ_taylor_e((double)n, ax, 1, 50, GSL_DBL_EPSILON, &t); result->val = t.val * ex; result->err = t.err * ex; result->err += 2.0 * GSL_DBL_EPSILON * fabs(result->val); if(x < 0.0 && GSL_IS_ODD(n)) result->val = -result->val; return stat_In; } else if(n < 150 && ax < 1e7) { gsl_sf_result I0_scaled; int stat_I0 = gsl_sf_bessel_I0_scaled_e(ax, &I0_scaled); double rat; int stat_CF1 = gsl_sf_bessel_I_CF1_ser((double)n, ax, &rat); double Ikp1 = rat * GSL_SQRT_DBL_MIN; double Ik = GSL_SQRT_DBL_MIN; double Ikm1; int k; for(k=n; k >= 1; k--) { Ikm1 = Ikp1 + 2.0*k/ax * Ik; Ikp1 = Ik; Ik = Ikm1; } result->val = I0_scaled.val * (GSL_SQRT_DBL_MIN / Ik); result->err = I0_scaled.err * (GSL_SQRT_DBL_MIN / Ik); result->err += 2.0 * GSL_DBL_EPSILON * fabs(result->val); if(x < 0.0 && GSL_IS_ODD(n)) result->val = -result->val; return GSL_ERROR_SELECT_2(stat_I0, stat_CF1); } else if( GSL_MIN( 0.29/(n*n), 0.5/(n*n + x*x) ) < 0.5*GSL_ROOT3_DBL_EPSILON) { int stat_as = gsl_sf_bessel_Inu_scaled_asymp_unif_e((double)n, ax, result); if(x < 0.0 && GSL_IS_ODD(n)) result->val = -result->val; return stat_as; } else { const int nhi = 2 + (int) (1.2 / GSL_ROOT6_DBL_EPSILON); gsl_sf_result r_Ikp1; gsl_sf_result r_Ik; int stat_a1 = gsl_sf_bessel_Inu_scaled_asymp_unif_e(nhi+1.0, ax, &r_Ikp1); int stat_a2 = gsl_sf_bessel_Inu_scaled_asymp_unif_e((double)nhi, ax, &r_Ik); double Ikp1 = r_Ikp1.val; double Ik = r_Ik.val; double Ikm1; int k; for(k=nhi; k > n; k--) { Ikm1 = Ikp1 + 2.0*k/ax * Ik; Ikp1 = Ik; Ik = Ikm1; } result->val = Ik; result->err = Ik * (r_Ikp1.err/r_Ikp1.val + r_Ik.err/r_Ik.val); if(x < 0.0 && GSL_IS_ODD(n)) result->val = -result->val; return GSL_ERROR_SELECT_2(stat_a1, stat_a2); } }
double gsl_sf_bessel_I1_scaled(const double x) { EVAL_RESULT(gsl_sf_bessel_I1_scaled_e(x, &result)); }