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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * This file incorporates work covered by the following license notice:
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed
+ * with this work for additional information regarding copyright
+ * ownership. The ASF licenses this file to you under the Apache
+ * License, Version 2.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of
+ * the License at http://www.apache.org/licenses/LICENSE-2.0 .
+ */
+
+#include "bessel.hxx"
+
+#include <rtl/math.hxx>
+
+#include <com/sun/star/lang/IllegalArgumentException.hpp>
+#include <com/sun/star/sheet/NoConvergenceException.hpp>
+
+using ::com::sun::star::lang::IllegalArgumentException;
+using ::com::sun::star::sheet::NoConvergenceException;
+
+namespace sca::analysis {
+
+const double f_PI = 3.1415926535897932385;
+const double f_PI_DIV_2 = f_PI / 2.0;
+const double f_PI_DIV_4 = f_PI / 4.0;
+const double f_2_DIV_PI = 2.0 / f_PI;
+
+
+// BESSEL J
+
+
+/* The BESSEL function, first kind, unmodified:
+ The algorithm follows
+ http://www.reference-global.com/isbn/978-3-11-020354-7
+ Numerical Mathematics 1 / Numerische Mathematik 1,
+ An algorithm-based introduction / Eine algorithmisch orientierte Einfuehrung
+ Deuflhard, Peter; Hohmann, Andreas
+ Berlin, New York (Walter de Gruyter) 2008
+ 4. ueberarb. u. erw. Aufl. 2008
+ eBook ISBN: 978-3-11-020355-4
+ Chapter 6.3.2 , algorithm 6.24
+ The source is in German.
+ The BesselJ-function is a special case of the adjoint summation with
+ a_k = 2*(k-1)/x for k=1,...
+ b_k = -1, for all k, directly substituted
+ m_0=1, m_k=2 for k even, and m_k=0 for k odd, calculated on the fly
+ alpha_k=1 for k=N and alpha_k=0 otherwise
+*/
+
+double BesselJ( double x, sal_Int32 N )
+
+{
+ if( N < 0 )
+ throw IllegalArgumentException();
+ if (x==0.0)
+ return (N==0) ? 1.0 : 0.0;
+
+ /* The algorithm works only for x>0, therefore remember sign. BesselJ
+ with integer order N is an even function for even N (means J(-x)=J(x))
+ and an odd function for odd N (means J(-x)=-J(x)).*/
+ double fSign = (N % 2 == 1 && x < 0) ? -1.0 : 1.0;
+ double fX = fabs(x);
+
+ const double fMaxIteration = 9000000.0; //experimental, for to return in < 3 seconds
+ double fEstimateIteration = fX * 1.5 + N;
+ bool bAsymptoticPossible = pow(fX,0.4) > N;
+ if (fEstimateIteration > fMaxIteration)
+ {
+ if (!bAsymptoticPossible)
+ throw NoConvergenceException();
+ return fSign * sqrt(f_2_DIV_PI/fX)* cos(fX-N*f_PI_DIV_2-f_PI_DIV_4);
+ }
+
+ double const epsilon = 1.0e-15; // relative error
+ bool bHasfound = false;
+ double k= 0.0;
+ // e_{-1} = 0; e_0 = alpha_0 / b_2
+ double u ; // u_0 = e_0/f_0 = alpha_0/m_0 = alpha_0
+
+ // first used with k=1
+ double m_bar; // m_bar_k = m_k * f_bar_{k-1}
+ double g_bar; // g_bar_k = m_bar_k - a_{k+1} + g_{k-1}
+ double g_bar_delta_u; // g_bar_delta_u_k = f_bar_{k-1} * alpha_k
+ // - g_{k-1} * delta_u_{k-1} - m_bar_k * u_{k-1}
+ // f_{-1} = 0.0; f_0 = m_0 / b_2 = 1/(-1) = -1
+ double g = 0.0; // g_0= f_{-1} / f_0 = 0/(-1) = 0
+ double delta_u = 0.0; // dummy initialize, first used with * 0
+ double f_bar = -1.0; // f_bar_k = 1/f_k, but only used for k=0
+
+ if (N==0)
+ {
+ //k=0; alpha_0 = 1.0
+ u = 1.0; // u_0 = alpha_0
+ // k = 1.0; at least one step is necessary
+ // m_bar_k = m_k * f_bar_{k-1} ==> m_bar_1 = 0.0
+ g_bar_delta_u = 0.0; // alpha_k = 0.0, m_bar = 0.0; g= 0.0
+ g_bar = - 2.0/fX; // k = 1.0, g = 0.0
+ delta_u = g_bar_delta_u / g_bar;
+ u = u + delta_u ; // u_k = u_{k-1} + delta_u_k
+ g = -1.0 / g_bar; // g_k=b_{k+2}/g_bar_k
+ f_bar = f_bar * g; // f_bar_k = f_bar_{k-1}* g_k
+ k = 2.0;
+ // From now on all alpha_k = 0.0 and k > N+1
+ }
+ else
+ { // N >= 1 and alpha_k = 0.0 for k<N
+ u=0.0; // u_0 = alpha_0
+ for (k =1.0; k<= N-1; k = k + 1.0)
+ {
+ m_bar=2.0 * fmod(k-1.0, 2.0) * f_bar;
+ g_bar_delta_u = - g * delta_u - m_bar * u; // alpha_k = 0.0
+ g_bar = m_bar - 2.0*k/fX + g;
+ delta_u = g_bar_delta_u / g_bar;
+ u = u + delta_u;
+ g = -1.0/g_bar;
+ f_bar=f_bar * g;
+ }
+ // Step alpha_N = 1.0
+ m_bar=2.0 * fmod(k-1.0, 2.0) * f_bar;
+ g_bar_delta_u = f_bar - g * delta_u - m_bar * u; // alpha_k = 1.0
+ g_bar = m_bar - 2.0*k/fX + g;
+ delta_u = g_bar_delta_u / g_bar;
+ u = u + delta_u;
+ g = -1.0/g_bar;
+ f_bar = f_bar * g;
+ k = k + 1.0;
+ }
+ // Loop until desired accuracy, always alpha_k = 0.0
+ do
+ {
+ m_bar = 2.0 * fmod(k-1.0, 2.0) * f_bar;
+ g_bar_delta_u = - g * delta_u - m_bar * u;
+ g_bar = m_bar - 2.0*k/fX + g;
+ delta_u = g_bar_delta_u / g_bar;
+ u = u + delta_u;
+ g = -1.0/g_bar;
+ f_bar = f_bar * g;
+ bHasfound = (fabs(delta_u)<=fabs(u)*epsilon);
+ k = k + 1.0;
+ }
+ while (!bHasfound && k <= fMaxIteration);
+ if (!bHasfound)
+ throw NoConvergenceException(); // unlikely to happen
+
+ return u * fSign;
+}
+
+
+// BESSEL I
+
+
+/* The BESSEL function, first kind, modified:
+
+ inf (x/2)^(n+2k)
+ I_n(x) = SUM TERM(n,k) with TERM(n,k) := --------------
+ k=0 k! (n+k)!
+
+ No asymptotic approximation used, see issue 43040.
+ */
+
+double BesselI( double x, sal_Int32 n )
+{
+ const sal_Int32 nMaxIteration = 2000;
+ const double fXHalf = x / 2.0;
+ if( n < 0 )
+ throw IllegalArgumentException();
+
+ double fResult = 0.0;
+
+ /* Start the iteration without TERM(n,0), which is set here.
+
+ TERM(n,0) = (x/2)^n / n!
+ */
+ sal_Int32 nK = 0;
+ double fTerm = 1.0;
+ // avoid overflow in Fak(n)
+ for( nK = 1; nK <= n; ++nK )
+ {
+ fTerm = fTerm / static_cast< double >( nK ) * fXHalf;
+ }
+ fResult = fTerm; // Start result with TERM(n,0).
+ if( fTerm != 0.0 )
+ {
+ nK = 1;
+ const double fEpsilon = 1.0E-15;
+ do
+ {
+ /* Calculation of TERM(n,k) from TERM(n,k-1):
+
+ (x/2)^(n+2k)
+ TERM(n,k) = --------------
+ k! (n+k)!
+
+ (x/2)^2 (x/2)^(n+2(k-1))
+ = --------------------------
+ k (k-1)! (n+k) (n+k-1)!
+
+ (x/2)^2 (x/2)^(n+2(k-1))
+ = --------- * ------------------
+ k(n+k) (k-1)! (n+k-1)!
+
+ x^2/4
+ = -------- TERM(n,k-1)
+ k(n+k)
+ */
+ fTerm = fTerm * fXHalf / static_cast<double>(nK) * fXHalf / static_cast<double>(nK+n);
+ fResult += fTerm;
+ nK++;
+ }
+ while( (fabs( fTerm ) > fabs(fResult) * fEpsilon) && (nK < nMaxIteration) );
+
+ }
+ return fResult;
+}
+
+/// @throws IllegalArgumentException
+/// @throws NoConvergenceException
+static double Besselk0( double fNum )
+{
+ double fRet;
+
+ if( fNum <= 2.0 )
+ {
+ double fNum2 = fNum * 0.5;
+ double y = fNum2 * fNum2;
+
+ fRet = -log( fNum2 ) * BesselI( fNum, 0 ) +
+ ( -0.57721566 + y * ( 0.42278420 + y * ( 0.23069756 + y * ( 0.3488590e-1 +
+ y * ( 0.262698e-2 + y * ( 0.10750e-3 + y * 0.74e-5 ) ) ) ) ) );
+ }
+ else
+ {
+ double y = 2.0 / fNum;
+
+ fRet = exp( -fNum ) / sqrt( fNum ) * ( 1.25331414 + y * ( -0.7832358e-1 +
+ y * ( 0.2189568e-1 + y * ( -0.1062446e-1 + y * ( 0.587872e-2 +
+ y * ( -0.251540e-2 + y * 0.53208e-3 ) ) ) ) ) );
+ }
+
+ return fRet;
+}
+
+/// @throws IllegalArgumentException
+/// @throws NoConvergenceException
+static double Besselk1( double fNum )
+{
+ double fRet;
+
+ if( fNum <= 2.0 )
+ {
+ double fNum2 = fNum * 0.5;
+ double y = fNum2 * fNum2;
+
+ fRet = log( fNum2 ) * BesselI( fNum, 1 ) +
+ ( 1.0 + y * ( 0.15443144 + y * ( -0.67278579 + y * ( -0.18156897 + y * ( -0.1919402e-1 +
+ y * ( -0.110404e-2 + y * -0.4686e-4 ) ) ) ) ) )
+ / fNum;
+ }
+ else
+ {
+ double y = 2.0 / fNum;
+
+ fRet = exp( -fNum ) / sqrt( fNum ) * ( 1.25331414 + y * ( 0.23498619 +
+ y * ( -0.3655620e-1 + y * ( 0.1504268e-1 + y * ( -0.780353e-2 +
+ y * ( 0.325614e-2 + y * -0.68245e-3 ) ) ) ) ) );
+ }
+
+ return fRet;
+}
+
+
+double BesselK( double fNum, sal_Int32 nOrder )
+{
+ switch( nOrder )
+ {
+ case 0: return Besselk0( fNum );
+ case 1: return Besselk1( fNum );
+ default:
+ {
+ double fTox = 2.0 / fNum;
+ double fBkm = Besselk0( fNum );
+ double fBk = Besselk1( fNum );
+
+ for( sal_Int32 n = 1 ; n < nOrder ; n++ )
+ {
+ const double fBkp = fBkm + double( n ) * fTox * fBk;
+ fBkm = fBk;
+ fBk = fBkp;
+ }
+
+ return fBk;
+ }
+ }
+}
+
+
+// BESSEL Y
+
+
+/* The BESSEL function, second kind, unmodified:
+ The algorithm for order 0 and for order 1 follows
+ http://www.reference-global.com/isbn/978-3-11-020354-7
+ Numerical Mathematics 1 / Numerische Mathematik 1,
+ An algorithm-based introduction / Eine algorithmisch orientierte Einfuehrung
+ Deuflhard, Peter; Hohmann, Andreas
+ Berlin, New York (Walter de Gruyter) 2008
+ 4. ueberarb. u. erw. Aufl. 2008
+ eBook ISBN: 978-3-11-020355-4
+ Chapter 6.3.2 , algorithm 6.24
+ The source is in German.
+ See #i31656# for a commented version of the implementation, attachment #desc6
+ https://bz.apache.org/ooo/attachment.cgi?id=63609
+*/
+
+/// @throws IllegalArgumentException
+/// @throws NoConvergenceException
+static double Bessely0( double fX )
+{
+ if (fX <= 0)
+ throw IllegalArgumentException();
+ const double fMaxIteration = 9000000.0; // should not be reached
+ if (fX > 5.0e+6) // iteration is not considerable better then approximation
+ return sqrt(1/f_PI/fX)
+ *(rtl::math::sin(fX)-rtl::math::cos(fX));
+ const double epsilon = 1.0e-15;
+ const double EulerGamma = 0.57721566490153286060;
+ double alpha = log(fX/2.0)+EulerGamma;
+ double u = alpha;
+
+ double k = 1.0;
+ double g_bar_delta_u = 0.0;
+ double g_bar = -2.0 / fX;
+ double delta_u = g_bar_delta_u / g_bar;
+ double g = -1.0/g_bar;
+ double f_bar = -1 * g;
+
+ double sign_alpha = 1.0;
+ bool bHasFound = false;
+ k = k + 1;
+ do
+ {
+ double km1mod2 = fmod(k-1.0, 2.0);
+ double m_bar = (2.0*km1mod2) * f_bar;
+ if (km1mod2 == 0.0)
+ alpha = 0.0;
+ else
+ {
+ alpha = sign_alpha * (4.0/k);
+ sign_alpha = -sign_alpha;
+ }
+ g_bar_delta_u = f_bar * alpha - g * delta_u - m_bar * u;
+ g_bar = m_bar - (2.0*k)/fX + g;
+ delta_u = g_bar_delta_u / g_bar;
+ u = u+delta_u;
+ g = -1.0 / g_bar;
+ f_bar = f_bar*g;
+ bHasFound = (fabs(delta_u)<=fabs(u)*epsilon);
+ k=k+1;
+ }
+ while (!bHasFound && k<fMaxIteration);
+ if (!bHasFound)
+ throw NoConvergenceException(); // not likely to happen
+ return u*f_2_DIV_PI;
+}
+
+// See #i31656# for a commented version of this implementation, attachment #desc6
+// https://bz.apache.org/ooo/attachment.cgi?id=63609
+/// @throws IllegalArgumentException
+/// @throws NoConvergenceException
+static double Bessely1( double fX )
+{
+ if (fX <= 0)
+ throw IllegalArgumentException();
+ const double fMaxIteration = 9000000.0; // should not be reached
+ if (fX > 5.0e+6) // iteration is not considerable better then approximation
+ return - sqrt(1/f_PI/fX)
+ *(rtl::math::sin(fX)+rtl::math::cos(fX));
+ const double epsilon = 1.0e-15;
+ const double EulerGamma = 0.57721566490153286060;
+ double alpha = 1.0/fX;
+ double f_bar = -1.0;
+ double u = alpha;
+ double k = 1.0;
+ alpha = 1.0 - EulerGamma - log(fX/2.0);
+ double g_bar_delta_u = -alpha;
+ double g_bar = -2.0 / fX;
+ double delta_u = g_bar_delta_u / g_bar;
+ u = u + delta_u;
+ double g = -1.0/g_bar;
+ f_bar = f_bar * g;
+ double sign_alpha = -1.0;
+ bool bHasFound = false;
+ k = k + 1.0;
+ do
+ {
+ double km1mod2 = fmod(k-1.0,2.0);
+ double m_bar = (2.0*km1mod2) * f_bar;
+ double q = (k-1.0)/2.0;
+ if (km1mod2 == 0.0) // k is odd
+ {
+ alpha = sign_alpha * (1.0/q + 1.0/(q+1.0));
+ sign_alpha = -sign_alpha;
+ }
+ else
+ alpha = 0.0;
+ g_bar_delta_u = f_bar * alpha - g * delta_u - m_bar * u;
+ g_bar = m_bar - (2.0*k)/fX + g;
+ delta_u = g_bar_delta_u / g_bar;
+ u = u+delta_u;
+ g = -1.0 / g_bar;
+ f_bar = f_bar*g;
+ bHasFound = (fabs(delta_u)<=fabs(u)*epsilon);
+ k=k+1;
+ }
+ while (!bHasFound && k<fMaxIteration);
+ if (!bHasFound)
+ throw NoConvergenceException();
+ return -u*2.0/f_PI;
+}
+
+double BesselY( double fNum, sal_Int32 nOrder )
+{
+ switch( nOrder )
+ {
+ case 0: return Bessely0( fNum );
+ case 1: return Bessely1( fNum );
+ default:
+ {
+ double fTox = 2.0 / fNum;
+ double fBym = Bessely0( fNum );
+ double fBy = Bessely1( fNum );
+
+ for( sal_Int32 n = 1 ; n < nOrder ; n++ )
+ {
+ const double fByp = double( n ) * fTox * fBy - fBym;
+ fBym = fBy;
+ fBy = fByp;
+ }
+
+ return fBy;
+ }
+ }
+}
+
+} // namespace sca::analysis
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */