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91 lines
1.9 KiB
91 lines
1.9 KiB
/* This file is part of the KDE project
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Copyright (C) 2001, The Karbon Developers
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Copyright (C) 2002, The Karbon Developers
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public
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License as published by the Free Software Foundation; either
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version 2 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public License
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along with this library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
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* Boston, MA 02110-1301, USA.
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*/
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#include <math.h>
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#include "vglobal.h"
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int
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VGlobal::binomialCoeff( unsigned n, unsigned k )
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{
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return
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static_cast<int>(
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0.5 +
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exp(
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factorialLn( n ) -
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factorialLn( k ) -
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factorialLn( n - k ) ) );
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}
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double
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VGlobal::factorialLn( unsigned n )
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{
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const unsigned cacheSize = 100;
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// A static array is initalized to zero.
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static double cache[ cacheSize ];
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if( n <= 1 )
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return 0.0;
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if( n <= cacheSize - 1 )
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{
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return cache[ n ]
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? cache[ n ]
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: ( cache[ n ] = gammaLn( n + 1.0 ) );
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}
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else
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{
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return gammaLn( n + 1.0 );
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}
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}
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double
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VGlobal::gammaLn( double x )
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{
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static double coeff[ 6 ] =
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{
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76.18009172947146,
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-86.50532032941677,
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24.01409824083091,
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-1.231739572450155,
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0.1208650973866179e-2,
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-0.5395239384953e-5
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};
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double y = x;
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double tmp = x + 5.5;
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tmp -= ( x + 0.5 ) * log( tmp );
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double ser = 1.000000000190015;
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for( int i = 0; i < 5; ++i )
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{
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ser += coeff[ i ] / ++y;
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}
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return -tmp + log( 2.5066282746310005 * ser / x );
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}
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