com.opengamma.strata.math.impl.cern.Bessel Maven / Gradle / Ivy
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/*
* Copyright (C) 2019 - present by OpenGamma Inc. and the OpenGamma group of companies
*
* Please see distribution for license.
*/
/*
* This code is copied from the original library from the `cern.jet.math` package.
*/
/*
Copyright © 1999 CERN - European Organization for Nuclear Research.
Permission to use, copy, modify, distribute and sell this software and its documentation for any purpose
is hereby granted without fee, provided that the above copyright notice appear in all copies and
that both that copyright notice and this permission notice appear in supporting documentation.
CERN makes no representations about the suitability of this software for any purpose.
It is provided "as is" without expressed or implied warranty.
*/
package com.opengamma.strata.math.impl.cern;
//CSOFF: ALL
/**
* Bessel and Airy functions.
*/
public class Bessel extends Constants {
/****************************************
* COEFFICIENTS FOR METHODS i0, i0e *
****************************************/
/**
* Chebyshev coefficients for exp(-x) I0(x)
* in the interval [0,8].
*
* lim(x->0){ exp(-x) I0(x) } = 1.
*/
protected static final double[] A_i0 = {
-4.41534164647933937950E-18,
3.33079451882223809783E-17,
-2.43127984654795469359E-16,
1.71539128555513303061E-15,
-1.16853328779934516808E-14,
7.67618549860493561688E-14,
-4.85644678311192946090E-13,
2.95505266312963983461E-12,
-1.72682629144155570723E-11,
9.67580903537323691224E-11,
-5.18979560163526290666E-10,
2.65982372468238665035E-9,
-1.30002500998624804212E-8,
6.04699502254191894932E-8,
-2.67079385394061173391E-7,
1.11738753912010371815E-6,
-4.41673835845875056359E-6,
1.64484480707288970893E-5,
-5.75419501008210370398E-5,
1.88502885095841655729E-4,
-5.76375574538582365885E-4,
1.63947561694133579842E-3,
-4.32430999505057594430E-3,
1.05464603945949983183E-2,
-2.37374148058994688156E-2,
4.93052842396707084878E-2,
-9.49010970480476444210E-2,
1.71620901522208775349E-1,
-3.04682672343198398683E-1,
6.76795274409476084995E-1
};
/**
* Chebyshev coefficients for exp(-x) sqrt(x) I0(x)
* in the inverted interval [8,infinity].
*
* lim(x->inf){ exp(-x) sqrt(x) I0(x) } = 1/sqrt(2pi).
*/
protected static final double[] B_i0 = {
-7.23318048787475395456E-18,
-4.83050448594418207126E-18,
4.46562142029675999901E-17,
3.46122286769746109310E-17,
-2.82762398051658348494E-16,
-3.42548561967721913462E-16,
1.77256013305652638360E-15,
3.81168066935262242075E-15,
-9.55484669882830764870E-15,
-4.15056934728722208663E-14,
1.54008621752140982691E-14,
3.85277838274214270114E-13,
7.18012445138366623367E-13,
-1.79417853150680611778E-12,
-1.32158118404477131188E-11,
-3.14991652796324136454E-11,
1.18891471078464383424E-11,
4.94060238822496958910E-10,
3.39623202570838634515E-9,
2.26666899049817806459E-8,
2.04891858946906374183E-7,
2.89137052083475648297E-6,
6.88975834691682398426E-5,
3.36911647825569408990E-3,
8.04490411014108831608E-1
};
/****************************************
* COEFFICIENTS FOR METHODS i1, i1e *
****************************************/
/**
* Chebyshev coefficients for exp(-x) I1(x) / x
* in the interval [0,8].
*
* lim(x->0){ exp(-x) I1(x) / x } = 1/2.
*/
protected static final double[] A_i1 = {
2.77791411276104639959E-18,
-2.11142121435816608115E-17,
1.55363195773620046921E-16,
-1.10559694773538630805E-15,
7.60068429473540693410E-15,
-5.04218550472791168711E-14,
3.22379336594557470981E-13,
-1.98397439776494371520E-12,
1.17361862988909016308E-11,
-6.66348972350202774223E-11,
3.62559028155211703701E-10,
-1.88724975172282928790E-9,
9.38153738649577178388E-9,
-4.44505912879632808065E-8,
2.00329475355213526229E-7,
-8.56872026469545474066E-7,
3.47025130813767847674E-6,
-1.32731636560394358279E-5,
4.78156510755005422638E-5,
-1.61760815825896745588E-4,
5.12285956168575772895E-4,
-1.51357245063125314899E-3,
4.15642294431288815669E-3,
-1.05640848946261981558E-2,
2.47264490306265168283E-2,
-5.29459812080949914269E-2,
1.02643658689847095384E-1,
-1.76416518357834055153E-1,
2.52587186443633654823E-1
};
/*
* Chebyshev coefficients for exp(-x) sqrt(x) I1(x)
* in the inverted interval [8,infinity].
*
* lim(x->inf){ exp(-x) sqrt(x) I1(x) } = 1/sqrt(2pi).
*/
protected static final double[] B_i1 = {
7.51729631084210481353E-18,
4.41434832307170791151E-18,
-4.65030536848935832153E-17,
-3.20952592199342395980E-17,
2.96262899764595013876E-16,
3.30820231092092828324E-16,
-1.88035477551078244854E-15,
-3.81440307243700780478E-15,
1.04202769841288027642E-14,
4.27244001671195135429E-14,
-2.10154184277266431302E-14,
-4.08355111109219731823E-13,
-7.19855177624590851209E-13,
2.03562854414708950722E-12,
1.41258074366137813316E-11,
3.25260358301548823856E-11,
-1.89749581235054123450E-11,
-5.58974346219658380687E-10,
-3.83538038596423702205E-9,
-2.63146884688951950684E-8,
-2.51223623787020892529E-7,
-3.88256480887769039346E-6,
-1.10588938762623716291E-4,
-9.76109749136146840777E-3,
7.78576235018280120474E-1
};
/****************************************
* COEFFICIENTS FOR METHODS k0, k0e *
****************************************/
/* Chebyshev coefficients for K0(x) + log(x/2) I0(x)
* in the interval [0,2]. The odd order coefficients are all
* zero; only the even order coefficients are listed.
*
* lim(x->0){ K0(x) + log(x/2) I0(x) } = -EUL.
*/
protected static final double[] A_k0 = {
1.37446543561352307156E-16,
4.25981614279661018399E-14,
1.03496952576338420167E-11,
1.90451637722020886025E-9,
2.53479107902614945675E-7,
2.28621210311945178607E-5,
1.26461541144692592338E-3,
3.59799365153615016266E-2,
3.44289899924628486886E-1,
-5.35327393233902768720E-1
};
/* Chebyshev coefficients for exp(x) sqrt(x) K0(x)
* in the inverted interval [2,infinity].
*
* lim(x->inf){ exp(x) sqrt(x) K0(x) } = sqrt(pi/2).
*/
protected static final double[] B_k0 = {
5.30043377268626276149E-18,
-1.64758043015242134646E-17,
5.21039150503902756861E-17,
-1.67823109680541210385E-16,
5.51205597852431940784E-16,
-1.84859337734377901440E-15,
6.34007647740507060557E-15,
-2.22751332699166985548E-14,
8.03289077536357521100E-14,
-2.98009692317273043925E-13,
1.14034058820847496303E-12,
-4.51459788337394416547E-12,
1.85594911495471785253E-11,
-7.95748924447710747776E-11,
3.57739728140030116597E-10,
-1.69753450938905987466E-9,
8.57403401741422608519E-9,
-4.66048989768794782956E-8,
2.76681363944501510342E-7,
-1.83175552271911948767E-6,
1.39498137188764993662E-5,
-1.28495495816278026384E-4,
1.56988388573005337491E-3,
-3.14481013119645005427E-2,
2.44030308206595545468E0
};
/****************************************
* COEFFICIENTS FOR METHODS k1, k1e *
****************************************/
/* Chebyshev coefficients for x(K1(x) - log(x/2) I1(x))
* in the interval [0,2].
*
* lim(x->0){ x(K1(x) - log(x/2) I1(x)) } = 1.
*/
protected static final double[] A_k1 = {
-7.02386347938628759343E-18,
-2.42744985051936593393E-15,
-6.66690169419932900609E-13,
-1.41148839263352776110E-10,
-2.21338763073472585583E-8,
-2.43340614156596823496E-6,
-1.73028895751305206302E-4,
-6.97572385963986435018E-3,
-1.22611180822657148235E-1,
-3.53155960776544875667E-1,
1.52530022733894777053E0
};
/* Chebyshev coefficients for exp(x) sqrt(x) K1(x)
* in the interval [2,infinity].
*
* lim(x->inf){ exp(x) sqrt(x) K1(x) } = sqrt(pi/2).
*/
protected static final double[] B_k1 = {
-5.75674448366501715755E-18,
1.79405087314755922667E-17,
-5.68946255844285935196E-17,
1.83809354436663880070E-16,
-6.05704724837331885336E-16,
2.03870316562433424052E-15,
-7.01983709041831346144E-15,
2.47715442448130437068E-14,
-8.97670518232499435011E-14,
3.34841966607842919884E-13,
-1.28917396095102890680E-12,
5.13963967348173025100E-12,
-2.12996783842756842877E-11,
9.21831518760500529508E-11,
-4.19035475934189648750E-10,
2.01504975519703286596E-9,
-1.03457624656780970260E-8,
5.74108412545004946722E-8,
-3.50196060308781257119E-7,
2.40648494783721712015E-6,
-1.93619797416608296024E-5,
1.95215518471351631108E-4,
-2.85781685962277938680E-3,
1.03923736576817238437E-1,
2.72062619048444266945E0
};
/**
* Makes this class non instantiable, but still let's others inherit from it.
*/
protected Bessel() {
}
/**
* Returns the modified Bessel function of order 0 of the
* argument.
*
* The function is defined as i0(x) = j0( ix ).
*
* The range is partitioned into the two intervals [0,8] and
* (8, infinity). Chebyshev polynomial expansions are employed
* in each interval.
*
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double i0(double x) throws ArithmeticException {
double y;
double absX = x < 0 ? -x : x;
if (absX <= 8.0) {
y = (absX / 2.0) - 2.0;
return (Math.exp(absX) * Arithmetic.chbevl(y, A_i0, 30));
}
return (Math.exp(absX) * Arithmetic.chbevl(32.0 / absX - 2.0, B_i0, 25) / Math.sqrt(absX));
}
/**
* Returns the exponentially scaled modified Bessel function
* of order 0 of the argument.
*
* The function is defined as i0e(x) = exp(-|x|) j0( ix ).
*
*
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double i0e(double x) throws ArithmeticException {
double y;
double absX = x < 0 ? -x : x;
if (absX <= 8.0) {
y = (absX / 2.0) - 2.0;
return (Arithmetic.chbevl(y, A_i0, 30));
}
return (Arithmetic.chbevl(32.0 / absX - 2.0, B_i0, 25) / Math.sqrt(absX));
}
/**
* Returns the modified Bessel function of order 1 of the
* argument.
*
* The function is defined as i1(x) = -i j1( ix ).
*
* The range is partitioned into the two intervals [0,8] and
* (8, infinity). Chebyshev polynomial expansions are employed
* in each interval.
*
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double i1(double x) throws ArithmeticException {
double y, z;
z = Math.abs(x);
if (z <= 8.0) {
y = (z / 2.0) - 2.0;
z = Arithmetic.chbevl(y, A_i1, 29) * z * Math.exp(z);
} else {
z = Math.exp(z) * Arithmetic.chbevl(32.0 / z - 2.0, B_i1, 25) / Math.sqrt(z);
}
if (x < 0.0)
z = -z;
return (z);
}
/**
* Returns the exponentially scaled modified Bessel function
* of order 1 of the argument.
*
* The function is defined as i1(x) = -i exp(-|x|) j1( ix ).
*
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double i1e(double x) throws ArithmeticException {
double y, z;
z = Math.abs(x);
if (z <= 8.0) {
y = (z / 2.0) - 2.0;
z = Arithmetic.chbevl(y, A_i1, 29) * z;
} else {
z = Arithmetic.chbevl(32.0 / z - 2.0, B_i1, 25) / Math.sqrt(z);
}
if (x < 0.0)
z = -z;
return (z);
}
/**
* Returns the Bessel function of the first kind of order 0 of the argument.
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double j0(double x) throws ArithmeticException {
double ax;
if ((ax = Math.abs(x)) < 8.0) {
double y = x * x;
double ans1 =
57568490574.0 + y * (-13362590354.0 + y * (651619640.7 + y * (-11214424.18 + y * (77392.33017 + y * (-184.9052456)))));
double ans2 = 57568490411.0 + y * (1029532985.0 + y * (9494680.718 + y * (59272.64853 + y * (267.8532712 + y * 1.0))));
return ans1 / ans2;
} else {
double z = 8.0 / ax;
double y = z * z;
double xx = ax - 0.785398164;
double ans1 = 1.0 + y * (-0.1098628627e-2 + y * (0.2734510407e-4 + y * (-0.2073370639e-5 + y * 0.2093887211e-6)));
double ans2 =
-0.1562499995e-1 + y * (0.1430488765e-3 + y * (-0.6911147651e-5 + y * (0.7621095161e-6 - y * 0.934935152e-7)));
return Math.sqrt(0.636619772 / ax) *
(Math.cos(xx) * ans1 - z * Math.sin(xx) * ans2);
}
}
/**
* Returns the Bessel function of the first kind of order 1 of the argument.
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double j1(double x) throws ArithmeticException {
double ax;
double y;
double ans1, ans2;
if ((ax = Math.abs(x)) < 8.0) {
y = x * x;
ans1 = x *
(72362614232.0 + y * (-7895059235.0 + y * (242396853.1 + y * (-2972611.439 + y * (15704.48260 + y * (-30.16036606))))));
ans2 = 144725228442.0 + y * (2300535178.0 + y * (18583304.74 + y * (99447.43394 + y * (376.9991397 + y * 1.0))));
return ans1 / ans2;
} else {
double z = 8.0 / ax;
double xx = ax - 2.356194491;
y = z * z;
ans1 = 1.0 + y * (0.183105e-2 + y * (-0.3516396496e-4 + y * (0.2457520174e-5 + y * (-0.240337019e-6))));
ans2 = 0.04687499995 + y * (-0.2002690873e-3 + y * (0.8449199096e-5 + y * (-0.88228987e-6 + y * 0.105787412e-6)));
double ans = Math.sqrt(0.636619772 / ax) *
(Math.cos(xx) * ans1 - z * Math.sin(xx) * ans2);
if (x < 0.0)
ans = -ans;
return ans;
}
}
/**
* Returns the Bessel function of the first kind of order n of the argument.
* @param n the order of the Bessel function.
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double jn(int n, double x) throws ArithmeticException {
int j, m;
double ax, bj, bjm, bjp, sum, tox, ans;
boolean jsum;
final double ACC = 40.0;
final double BIGNO = 1.0e+10;
final double BIGNI = 1.0e-10;
if (n == 0)
return j0(x);
if (n == 1)
return j1(x);
ax = Math.abs(x);
if (ax == 0.0)
return 0.0;
if (ax > (double) n) {
tox = 2.0 / ax;
bjm = j0(ax);
bj = j1(ax);
for (j = 1; j < n; j++) {
bjp = j * tox * bj - bjm;
bjm = bj;
bj = bjp;
}
ans = bj;
} else {
tox = 2.0 / ax;
m = 2 * ((n + (int) Math.sqrt(ACC * n)) / 2);
jsum = false;
bjp = ans = sum = 0.0;
bj = 1.0;
for (j = m; j > 0; j--) {
bjm = j * tox * bj - bjp;
bjp = bj;
bj = bjm;
if (Math.abs(bj) > BIGNO) {
bj *= BIGNI;
bjp *= BIGNI;
ans *= BIGNI;
sum *= BIGNI;
}
if (jsum)
sum += bj;
jsum = !jsum;
if (j == n)
ans = bjp;
}
sum = 2.0 * sum - bj;
ans /= sum;
}
return x < 0.0 && n % 2 == 1 ? -ans : ans;
}
/**
* Returns the modified Bessel function of the third kind
* of order 0 of the argument.
*
* The range is partitioned into the two intervals [0,8] and
* (8, infinity). Chebyshev polynomial expansions are employed
* in each interval.
*
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double k0(double x) throws ArithmeticException {
double y, z;
if (x <= 0.0)
throw new ArithmeticException();
if (x <= 2.0) {
y = x * x - 2.0;
y = Arithmetic.chbevl(y, A_k0, 10) - Math.log(0.5 * x) * i0(x);
return (y);
}
z = 8.0 / x - 2.0;
y = Math.exp(-x) * Arithmetic.chbevl(z, B_k0, 25) / Math.sqrt(x);
return (y);
}
/**
* Returns the exponentially scaled modified Bessel function
* of the third kind of order 0 of the argument.
*
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double k0e(double x) throws ArithmeticException {
double y;
if (x <= 0.0)
throw new ArithmeticException();
if (x <= 2.0) {
y = x * x - 2.0;
y = Arithmetic.chbevl(y, A_k0, 10) - Math.log(0.5 * x) * i0(x);
return (y * Math.exp(x));
}
y = Arithmetic.chbevl(8.0 / x - 2.0, B_k0, 25) / Math.sqrt(x);
return (y);
}
/**
* Returns the modified Bessel function of the third kind
* of order 1 of the argument.
*
* The range is partitioned into the two intervals [0,2] and
* (2, infinity). Chebyshev polynomial expansions are employed
* in each interval.
*
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double k1(double x) throws ArithmeticException {
double y, z;
z = 0.5 * x;
if (z <= 0.0)
throw new ArithmeticException();
if (x <= 2.0) {
y = x * x - 2.0;
y = Math.log(z) * i1(x) + Arithmetic.chbevl(y, A_k1, 11) / x;
return (y);
}
return (Math.exp(-x) * Arithmetic.chbevl(8.0 / x - 2.0, B_k1, 25) / Math.sqrt(x));
}
/**
* Returns the exponentially scaled modified Bessel function
* of the third kind of order 1 of the argument.
*
* k1e(x) = exp(x) * k1(x).
*
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double k1e(double x) throws ArithmeticException {
double y;
if (x <= 0.0)
throw new ArithmeticException();
if (x <= 2.0) {
y = x * x - 2.0;
y = Math.log(0.5 * x) * i1(x) + Arithmetic.chbevl(y, A_k1, 11) / x;
return (y * Math.exp(x));
}
return (Arithmetic.chbevl(8.0 / x - 2.0, B_k1, 25) / Math.sqrt(x));
}
/**
* Returns the modified Bessel function of the third kind
* of order nn of the argument.
*
* The range is partitioned into the two intervals [0,9.55] and
* (9.55, infinity). An ascending power series is used in the
* low range, and an asymptotic expansion in the high range.
*
* @param nn the order of the Bessel function.
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double kn(int nn, double x) throws ArithmeticException {
/*
Algorithm for Kn.
n-1
-n - (n-k-1)! 2 k
K (x) = 0.5 (x/2) > -------- (-x /4)
n - k!
k=0
inf. 2 k
n n - (x /4)
+ (-1) 0.5(x/2) > {p(k+1) + p(n+k+1) - 2log(x/2)} ---------
- k! (n+k)!
k=0
where p(m) is the psi function: p(1) = -EUL and
m-1
-
p(m) = -EUL + > 1/k
-
k=1
For large x,
2 2 2
u-1 (u-1 )(u-3 )
K (z) = sqrt(pi/2z) exp(-z) { 1 + ------- + ------------ + ...}
v 1 2
1! (8z) 2! (8z)
asymptotically, where
2
u = 4 v .
*/
final double EUL = 5.772156649015328606065e-1;
final double MAXNUM = Double.MAX_VALUE;
final int MAXFAC = 31;
double k, kf, nk1f, nkf, zn, t, s, z0, z;
double ans, fn, pn, pk, zmn, tlg, tox;
int i, n;
if (nn < 0)
n = -nn;
else
n = nn;
if (n > MAXFAC)
throw new ArithmeticException("Overflow");
if (x <= 0.0)
throw new IllegalArgumentException();
if (x <= 9.55) {
ans = 0.0;
z0 = 0.25 * x * x;
fn = 1.0;
pn = 0.0;
zmn = 1.0;
tox = 2.0 / x;
if (n > 0) {
/* compute factorial of n and psi(n) */
pn = -EUL;
k = 1.0;
for (i = 1; i < n; i++) {
pn += 1.0 / k;
k += 1.0;
fn *= k;
}
zmn = tox;
if (n == 1) {
ans = 1.0 / x;
} else {
nk1f = fn / n;
kf = 1.0;
s = nk1f;
z = -z0;
zn = 1.0;
for (i = 1; i < n; i++) {
nk1f = nk1f / (n - i);
kf = kf * i;
zn *= z;
t = nk1f * zn / kf;
s += t;
if ((MAXNUM - Math.abs(t)) < Math.abs(s))
throw new ArithmeticException("Overflow");
if ((tox > 1.0) && ((MAXNUM / tox) < zmn))
throw new ArithmeticException("Overflow");
zmn *= tox;
}
s *= 0.5;
t = Math.abs(s);
if ((zmn > 1.0) && ((MAXNUM / zmn) < t))
throw new ArithmeticException("Overflow");
if ((t > 1.0) && ((MAXNUM / t) < zmn))
throw new ArithmeticException("Overflow");
ans = s * zmn;
}
}
tlg = 2.0 * Math.log(0.5 * x);
pk = -EUL;
if (n == 0) {
pn = pk;
t = 1.0;
} else {
pn = pn + 1.0 / n;
t = 1.0 / fn;
}
s = (pk + pn - tlg) * t;
k = 1.0;
do {
t *= z0 / (k * (k + n));
pk += 1.0 / k;
pn += 1.0 / (k + n);
s += (pk + pn - tlg) * t;
k += 1.0;
} while (Math.abs(t / s) > MACHEP);
s = 0.5 * s / zmn;
if ((n & 1) > 0)
s = -s;
ans += s;
return (ans);
}
/* Asymptotic expansion for Kn(x) */
/* Converges to 1.4e-17 for x > 18.4 */
if (x > MAXLOG)
throw new ArithmeticException("Underflow");
k = n;
pn = 4.0 * k * k;
pk = 1.0;
z0 = 8.0 * x;
fn = 1.0;
t = 1.0;
s = t;
nkf = MAXNUM;
i = 0;
do {
z = pn - pk * pk;
t = t * z / (fn * z0);
nk1f = Math.abs(t);
if ((i >= n) && (nk1f > nkf)) {
ans = Math.exp(-x) * Math.sqrt(Math.PI / (2.0 * x)) * s;
return (ans);
}
nkf = nk1f;
s += t;
fn += 1.0;
pk += 2.0;
i += 1;
} while (Math.abs(t / s) > MACHEP);
ans = Math.exp(-x) * Math.sqrt(Math.PI / (2.0 * x)) * s;
return (ans);
}
/**
* Returns the Bessel function of the second kind of order 0 of the argument.
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double y0(double x) throws ArithmeticException {
if (x < 8.0) {
double y = x * x;
double ans1 =
-2957821389.0 + y * (7062834065.0 + y * (-512359803.6 + y * (10879881.29 + y * (-86327.92757 + y * 228.4622733))));
double ans2 = 40076544269.0 + y * (745249964.8 + y * (7189466.438 + y * (47447.26470 + y * (226.1030244 + y * 1.0))));
return (ans1 / ans2) + 0.636619772 * j0(x) * Math.log(x);
} else {
double z = 8.0 / x;
double y = z * z;
double xx = x - 0.785398164;
double ans1 = 1.0 + y * (-0.1098628627e-2 + y * (0.2734510407e-4 + y * (-0.2073370639e-5 + y * 0.2093887211e-6)));
double ans2 =
-0.1562499995e-1 + y * (0.1430488765e-3 + y * (-0.6911147651e-5 + y * (0.7621095161e-6 + y * (-0.934945152e-7))));
return Math.sqrt(0.636619772 / x) *
(Math.sin(xx) * ans1 + z * Math.cos(xx) * ans2);
}
}
/**
* Returns the Bessel function of the second kind of order 1 of the argument.
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double y1(double x) throws ArithmeticException {
if (x < 8.0) {
double y = x * x;
double ans1 = x * (-0.4900604943e13 +
y * (0.1275274390e13 + y * (-0.5153438139e11 + y * (0.7349264551e9 + y * (-0.4237922726e7 + y * 0.8511937935e4)))));
double ans2 = 0.2499580570e14 +
y * (0.4244419664e12 + y * (0.3733650367e10 + y * (0.2245904002e8 + y * (0.1020426050e6 + y * (0.3549632885e3 + y)))));
return (ans1 / ans2) + 0.636619772 * (j1(x) * Math.log(x) - 1.0 / x);
} else {
double z = 8.0 / x;
double y = z * z;
double xx = x - 2.356194491;
double ans1 = 1.0 + y * (0.183105e-2 + y * (-0.3516396496e-4 + y * (0.2457520174e-5 + y * (-0.240337019e-6))));
double ans2 = 0.04687499995 + y * (-0.2002690873e-3 + y * (0.8449199096e-5 + y * (-0.88228987e-6 + y * 0.105787412e-6)));
return Math.sqrt(0.636619772 / x) *
(Math.sin(xx) * ans1 + z * Math.cos(xx) * ans2);
}
}
/**
* Returns the Bessel function of the second kind of order n of the argument.
* @param n the order of the Bessel function.
* @param x the value to compute the bessel function of.
* @return result
* @throws ArithmeticException error
*/
static public double yn(int n, double x) throws ArithmeticException {
double by, bym, byp, tox;
if (n == 0)
return y0(x);
if (n == 1)
return y1(x);
tox = 2.0 / x;
by = y1(x);
bym = y0(x);
for (int j = 1; j < n; j++) {
byp = j * tox * by - bym;
bym = by;
by = byp;
}
return by;
}
}