mirror of
https://github.com/vale981/arb
synced 2025-03-05 09:21:38 -05:00
59 lines
1.5 KiB
C
59 lines
1.5 KiB
C
/*
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Copyright (C) 2015 Fredrik Johansson
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This file is part of Arb.
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Arb is free software: you can redistribute it and/or modify it under
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the terms of the GNU Lesser General Public License (LGPL) as published
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by the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version. See <http://www.gnu.org/licenses/>.
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*/
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#include "acb_hypgeom.h"
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#define ALWAYS1 (0.25 * 0.25)
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#define ALWAYS2 (0.75 * 0.75)
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#define LIMIT (0.75 * 0.75)
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int
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acb_hypgeom_2f1_choose(const acb_t z)
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{
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double x, y;
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double mag[7];
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int i, pick;
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x = arf_get_d(arb_midref(acb_realref(z)), ARF_RND_DOWN);
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y = arf_get_d(arb_midref(acb_imagref(z)), ARF_RND_DOWN);
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x = FLINT_MAX(FLINT_MIN(x, 1e10), -1e10);
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y = FLINT_MAX(FLINT_MIN(y, 1e10), -1e10);
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mag[0] = x*x + y*y; /* |z|^2 */
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mag[4] = (1.0-x)*(1.0-x) + y*y; /* |1-z|^2 */
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if (mag[0] <= ALWAYS1) return 0;
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mag[1] = mag[0] / FLINT_MAX(mag[4], 1e-10); /* |z/(z-1)|^2 */
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if (mag[1] <= ALWAYS1) return 1;
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if (mag[0] <= ALWAYS2 || mag[1] <= ALWAYS2)
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return mag[0] <= mag[1] ? 0 : 1;
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mag[2] = 1.0 / mag[0]; /* |1/z|^2 */
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mag[3] = 1.0 / FLINT_MAX(mag[4], 1e-10); /* 1/|1-z|^2 */
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mag[5] = mag[4] / mag[0]; /* |1-1/z|^2 = |(1-z)/z|^2 */
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pick = 0;
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for (i = 1; i < 6; i++)
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{
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if (mag[i] < mag[pick])
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pick = i;
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}
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if (mag[pick] <= LIMIT)
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return pick;
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return 6;
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}
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