mirror of
https://github.com/vale981/arb
synced 2025-03-05 09:21:38 -05:00
6bf072eb59
This will allow us to not loose the julia session on error. See also https://github.com/wbhart/flint2/pull/243
92 lines
2.4 KiB
C
92 lines
2.4 KiB
C
/*
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Copyright (C) 2013 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 "arb_poly.h"
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#define CUTOFF 5
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void
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_arb_poly_revert_series_newton(arb_ptr Qinv, arb_srcptr Q, slong Qlen, slong n, slong prec)
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{
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slong i, k, a[FLINT_BITS];
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arb_ptr T, U, V;
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if (n <= 2)
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{
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if (n >= 1)
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arb_zero(Qinv);
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if (n == 2)
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arb_inv(Qinv + 1, Q + 1, prec);
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return;
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}
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T = _arb_vec_init(n);
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U = _arb_vec_init(n);
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V = _arb_vec_init(n);
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k = n;
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for (i = 1; (WORD(1) << i) < k; i++);
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a[i = 0] = k;
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while (k >= CUTOFF)
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a[++i] = (k = (k + 1) / 2);
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_arb_poly_revert_series_lagrange(Qinv, Q, Qlen, k, prec);
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_arb_vec_zero(Qinv + k, n - k);
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for (i--; i >= 0; i--)
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{
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k = a[i];
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_arb_poly_compose_series(T, Q, FLINT_MIN(Qlen, k), Qinv, k, k, prec);
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_arb_poly_derivative(U, T, k, prec); arb_zero(U + k - 1);
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arb_zero(T + 1);
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_arb_poly_div_series(V, T, k, U, k, k, prec);
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_arb_poly_derivative(T, Qinv, k, prec);
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_arb_poly_mullow(U, V, k, T, k, k, prec);
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_arb_vec_sub(Qinv, Qinv, U, k, prec);
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}
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_arb_vec_clear(T, n);
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_arb_vec_clear(U, n);
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_arb_vec_clear(V, n);
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}
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void
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arb_poly_revert_series_newton(arb_poly_t Qinv,
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const arb_poly_t Q, slong n, slong prec)
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{
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slong Qlen = Q->length;
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if (Qlen < 2 || !arb_is_zero(Q->coeffs)
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|| arb_contains_zero(Q->coeffs + 1))
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{
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flint_printf("Exception (arb_poly_revert_series_newton). Input must \n"
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"have zero constant term and nonzero coefficient of x^1.\n");
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flint_abort();
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}
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if (Qinv != Q)
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{
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arb_poly_fit_length(Qinv, n);
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_arb_poly_revert_series_newton(Qinv->coeffs, Q->coeffs, Qlen, n, prec);
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}
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else
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{
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arb_poly_t t;
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arb_poly_init2(t, n);
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_arb_poly_revert_series_newton(t->coeffs, Q->coeffs, Qlen, n, prec);
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arb_poly_swap(Qinv, t);
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arb_poly_clear(t);
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}
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_arb_poly_set_length(Qinv, n);
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_arb_poly_normalise(Qinv);
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}
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