fps/berlekamp-massey.hpp

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• Last update: 2020-12-05 08:16:44+09:00
• Include: #include "fps/berlekamp-massey.hpp"

Required by

• 線形回帰数列の高速計算(Berlekamp-Massey/Bostan-Mori) (fps/nth-term.hpp)
• Black Box Linear Algebra (matrix/black-box-linear-algebra.hpp)

Verified with

• verify/verify-yosupo-fps/yosupo-linear-recurrence.test.cpp
• verify/verify-yosupo-math/yosupo-determinant-of-matrix-bbla.test.cpp
• verify/verify-yosupo-math/yosupo-determinant-of-sparse-matrix-bbla.test.cpp
• verify/verify-yuki/yuki-0215-nth-term.test.cpp
• verify/verify-yuki/yuki-1112-sparse.test.cpp
• verify/verify-yuki/yuki-1112.test.cpp

Code

#pragma once

template <typename mint>
vector<mint> BerlekampMassey(const vector<mint> &s) {
  const int N = (int)s.size();
  vector<mint> b, c;
  b.reserve(N + 1);
  c.reserve(N + 1);
  b.push_back(mint(1));
  c.push_back(mint(1));
  mint y = mint(1);
  for (int ed = 1; ed <= N; ed++) {
    int l = int(c.size()), m = int(b.size());
    mint x = 0;
    for (int i = 0; i < l; i++) x += c[i] * s[ed - l + i];
    b.emplace_back(mint(0));
    m++;
    if (x == mint(0)) continue;
    mint freq = x / y;
    if (l < m) {
      auto tmp = c;
      c.insert(begin(c), m - l, mint(0));
      for (int i = 0; i < m; i++) c[m - 1 - i] -= freq * b[m - 1 - i];
      b = tmp;
      y = x;
    } else {
      for (int i = 0; i < m; i++) c[l - 1 - i] -= freq * b[m - 1 - i];
    }
  }
  reverse(begin(c), end(c));
  return c;
}

#line 2 "fps/berlekamp-massey.hpp"

template <typename mint>
vector<mint> BerlekampMassey(const vector<mint> &s) {
  const int N = (int)s.size();
  vector<mint> b, c;
  b.reserve(N + 1);
  c.reserve(N + 1);
  b.push_back(mint(1));
  c.push_back(mint(1));
  mint y = mint(1);
  for (int ed = 1; ed <= N; ed++) {
    int l = int(c.size()), m = int(b.size());
    mint x = 0;
    for (int i = 0; i < l; i++) x += c[i] * s[ed - l + i];
    b.emplace_back(mint(0));
    m++;
    if (x == mint(0)) continue;
    mint freq = x / y;
    if (l < m) {
      auto tmp = c;
      c.insert(begin(c), m - l, mint(0));
      for (int i = 0; i < m; i++) c[m - 1 - i] -= freq * b[m - 1 - i];
      b = tmp;
      y = x;
    } else {
      for (int i = 0; i < m; i++) c[l - 1 - i] -= freq * b[m - 1 - i];
    }
  }
  reverse(begin(c), end(c));
  return c;
}

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