/*
    Copyright (C) 2016  Ralf Stephan

    This file is part of FLINT.

    FLINT is free software: you can redistribute it and/or modify it under
    the terms of the GNU Lesser General Public License (LGPL) as published
    by the Free Software Foundation; either version 2.1 of the License, or
    (at your option) any later version.  See <https://www.gnu.org/licenses/>.
*/

#include "fmpz_poly.h"

int main()
{
    fmpz_poly_t T0, T1, T2, t, tt;
    slong n;

    FLINT_TEST_INIT(state);

    flint_printf("legendre_pt....");
    fflush(stdout);

    fmpz_poly_init(T0);
    fmpz_poly_init(T1);
    fmpz_poly_init(T2);
    fmpz_poly_init(t);
    fmpz_poly_init(tt);

    fmpz_poly_legendre_pt(T0, 0);
    fmpz_poly_legendre_pt(T1, 1);

    for (n = 1; n <= 500; n++)
    {
        fmpz_poly_legendre_pt(T2, n+1);
        fmpz_poly_set(t, T1);

        /* Verify (n+1)P_{n+1} = (2n+1)(2x-1) P_n - nP_{n-1} */
        fmpz_poly_shift_left(t, t, 1);
        fmpz_poly_scalar_mul_ui(t, t, 2);
        fmpz_poly_sub(t, t, T1);
        fmpz_poly_scalar_mul_ui(t, t, 2*n+1);
        fmpz_poly_scalar_mul_ui(tt, T0, n);
        fmpz_poly_sub(t, t, tt);
        fmpz_poly_scalar_mul_ui(tt, T2, n+1);

        if (!fmpz_poly_equal(t, tt))
        {
            flint_printf("FAIL: n = %wd\n", n);
            flint_printf("t: "); fmpz_poly_print_pretty(t, "x"); flint_printf("\n");
            flint_printf("tt: "); fmpz_poly_print_pretty(tt, "x"); flint_printf("\n");
            abort();
        }

        fmpz_poly_swap(T0, T1);
        fmpz_poly_swap(T1, T2);
    }

    fmpz_poly_clear(T0);
    fmpz_poly_clear(T1);
    fmpz_poly_clear(T2);
    fmpz_poly_clear(t);
    fmpz_poly_clear(tt);

    FLINT_TEST_CLEANUP(state);
    flint_printf("PASS\n");
    return 0;
}