casadi_kron_contract_inner_sparse_dense.hpp

//
//    MIT No Attribution
//
//    Copyright (C) 2010-2023 Joel Andersson, Joris Gillis, Moritz Diehl, KU Leuven.
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// SYMBOL "kron_contract_inner_sparse_dense"
// y[i,j] = sum_{r,s} m[i*mB+r, j*nB+s] * b[r,s]
// where m has CSC sparsity sp_m (mA*mB, nA*nB), b is dense (mB, nB),
// y has CSC sparsity sp_y (mA, nA). Walks m's nonzeros only; no densify-into-w
// step needed since b is already dense.
template<typename T1>
void casadi_kron_contract_inner_sparse_dense(const T1* m, const casadi_int* sp_m,
                                             const T1* b, casadi_int mB, casadi_int nB,
                                             T1* y, const casadi_int* sp_y) {
    casadi_int nA = sp_y[1];
    const casadi_int* y_colind = sp_y+2;
    const casadi_int* y_row    = sp_y+2+nA+1;
    casadi_int m_ncol = sp_m[1];
    const casadi_int* m_colind = sp_m+2;
    const casadi_int* m_row    = sp_m+2+m_ncol+1;
    casadi_int cc, j, s, el, rr, i, r, y_el, y_col_start, y_col_end, k;
    T1 b_val;
    for (k=0; k<y_colind[nA]; ++k) y[k] = 0;
    // Nested (j, s) loop avoids per-column cc / nB and cc % nB.
    for (j=0; j<nA; ++j) {
      y_col_start = y_colind[j];
      y_col_end = y_colind[j+1];
      if (y_col_start == y_col_end) continue;
      for (s=0; s<nB; ++s) {
        cc = j*nB + s;
        for (el=m_colind[cc]; el<m_colind[cc+1]; ++el) {
          rr = m_row[el];
          i = rr / mB;
          r = rr % mB;
          b_val = b[s*mB + r];
          for (y_el=y_col_start; y_el<y_col_end; ++y_el) {
            if (y_row[y_el] == i) { y[y_el] += m[el] * b_val; break; }
            if (y_row[y_el] > i) break;
          }
        }
      }
    }
}