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/* statistics/quantiles_source.c
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*
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* Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 Jim Davies, Brian Gough
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or (at
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* your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* 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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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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double
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FUNCTION(gsl_stats,quantile_from_sorted_data) (const BASE sorted_data[],
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const size_t stride,
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const size_t n,
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const double f)
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{
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const double index = f * (n - 1) ;
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const size_t lhs = (int)index ;
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const double delta = index - lhs ;
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double result;
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if (n == 0)
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return 0.0 ;
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if (lhs == n - 1)
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{
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result = sorted_data[lhs * stride] ;
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}
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else
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{
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result = (1 - delta) * sorted_data[lhs * stride] + delta * sorted_data[(lhs + 1) * stride] ;
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}
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return result ;
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}
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