lazy_det_operation.hpp

// Copyright (c) 2017--present, The Simons Foundation
// This file is part of TRIQS/ctint and is licensed under the terms of GPLv3 or later.
// SPDX-License-Identifier: GPL-3.0-or-later
// See LICENSE in the root of this distribution for details.
 
#pragma once
#include "vertex.hpp"
#include "dets.hpp"
 
namespace triqs_ctint {

  class lazy_det_operation_t {
 
    private:
    // Vector of all determinants
    std::vector<det_t> *dets;
 
    // This type keeps track of lazy inserts for single determinant
    struct one_block {
      // Vector of $c$ (x) and $c^\dagger$ (y) operators
      std::vector<c_t> c_lst       = {};
      std::vector<cdag_t> cdag_lst = {};
 
      // Lazy-add a $c$ operator
      void lazy_add_c(c_t const &c_) { c_lst.emplace_back(c_); }
 
      // Lazy-add a $c^\dagger$ operator
      void lazy_add_cdag(cdag_t const &cdag_) { cdag_lst.emplace_back(cdag_); }
 
      // Tries to perform all insertions into the det, returning the det ratio
      g_tau_scalar_t execute_try_insert(det_t *d);
 
      // Tries to perform all removals from the det, returning the det ratio
      g_tau_scalar_t execute_try_remove(det_t *d);
 
      // Tries to perform all spinflips from the det, returning the det ratio
      g_tau_scalar_t execute_try_change_col_row(det_t *d);
    };
 
    // The list of lazy operations, one for each determinant
    std::vector<one_block> lazy_op_lst;
 
    public:
    lazy_det_operation_t(std::vector<det_t> *dets) : dets(dets), lazy_op_lst(dets->size()) {}

    void reset() {
      for (auto &l : lazy_op_lst) {
        l.c_lst.clear();
        l.cdag_lst.clear();
      }
    }

    lazy_det_operation_t &operator<<(vertex_t const &v) {
      // Separately lazy-add all four operators associated with this vertex
      lazy_op_lst[v.idx.b1].lazy_add_cdag(cdag_t{v.tau1, v.idx.u1, v.vertex_label, 0, v.s}); //c^\dagger
      lazy_op_lst[v.idx.b2].lazy_add_c(c_t{v.tau2, v.idx.u2, v.vertex_label, 0, v.s});       //c
      lazy_op_lst[v.idx.b3].lazy_add_cdag(cdag_t{v.tau3, v.idx.u3, v.vertex_label, 1, v.s}); //c^\dagger
      lazy_op_lst[v.idx.b4].lazy_add_c(c_t{v.tau4, v.idx.u4, v.vertex_label, 1, v.s});       //c
      return *this;
    }

    g_tau_scalar_t execute_try_insert() {
      g_tau_scalar_t det_ratio = 1.0;
      for (auto i : range(dets->size())) det_ratio *= lazy_op_lst[i].execute_try_insert(&(*dets)[i]);
      reset();
      return det_ratio;
    }

    g_tau_scalar_t execute_try_remove() {
      g_tau_scalar_t det_ratio = 1.0;
      for (auto i : range(dets->size())) det_ratio *= lazy_op_lst[i].execute_try_remove(&(*dets)[i]);
      reset();
      return det_ratio;
    }

    g_tau_scalar_t execute_try_change_col_row() {
      g_tau_scalar_t det_ratio = 1.0;
      for (auto i : range(dets->size())) det_ratio *= lazy_op_lst[i].execute_try_change_col_row(&(*dets)[i]);
      reset();
      return det_ratio;
    }
  };
} // namespace triqs_ctint