mirror of
https://github.com/vale981/arb
synced 2025-03-06 01:41:39 -05:00
97 lines
2.8 KiB
C
97 lines
2.8 KiB
C
/*=============================================================================
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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
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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 2 of the License, or
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(at your option) any later version.
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ARB 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
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with ARB; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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=============================================================================*/
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/******************************************************************************
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Copyright (C) 2013 Fredrik Johansson
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******************************************************************************/
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#include "acb_poly.h"
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void
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_acb_poly_revert_series_lagrange(acb_ptr Qinv,
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acb_srcptr Q, slong Qlen, slong n, slong prec)
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{
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slong i;
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acb_ptr R, S, T, tmp;
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if (n <= 2)
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{
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if (n >= 1)
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acb_zero(Qinv);
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if (n == 2)
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acb_inv(Qinv + 1, Q + 1, prec);
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return;
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}
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R = _acb_vec_init(n - 1);
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S = _acb_vec_init(n - 1);
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T = _acb_vec_init(n - 1);
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acb_zero(Qinv);
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acb_inv(Qinv + 1, Q + 1, prec);
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_acb_poly_inv_series(R, Q + 1, FLINT_MIN(Qlen, n) - 1, n - 1, prec);
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_acb_vec_set(S, R, n - 1);
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for (i = 2; i < n; i++)
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{
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_acb_poly_mullow(T, S, n - 1, R, n - 1, n - 1, prec);
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acb_div_ui(Qinv + i, T + i - 1, i, prec);
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tmp = S; S = T; T = tmp;
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}
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_acb_vec_clear(R, n - 1);
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_acb_vec_clear(S, n - 1);
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_acb_vec_clear(T, n - 1);
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}
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void
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acb_poly_revert_series_lagrange(acb_poly_t Qinv,
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const acb_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 || !acb_is_zero(Q->coeffs)
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|| acb_contains_zero(Q->coeffs + 1))
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{
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flint_printf("Exception (acb_poly_revert_series_lagrange). Input must \n"
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"have zero constant term and nonzero coefficient of x^1.\n");
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abort();
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}
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if (Qinv != Q)
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{
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acb_poly_fit_length(Qinv, n);
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_acb_poly_revert_series_lagrange(Qinv->coeffs, Q->coeffs, Qlen, n, prec);
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}
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else
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{
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acb_poly_t t;
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acb_poly_init2(t, n);
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_acb_poly_revert_series_lagrange(t->coeffs, Q->coeffs, Qlen, n, prec);
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acb_poly_swap(Qinv, t);
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acb_poly_clear(t);
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}
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_acb_poly_set_length(Qinv, n);
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_acb_poly_normalise(Qinv);
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}
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