tridiag_complex.cpp

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#include "linalg/factorization/tridiag_complex.hpp"
 
namespace num {
 
void ComplexTriDiag::factor(int n_, cplx a_, cplx b_, cplx c_) {
    n       = n_;
    a_coeff = a_;
 
    c_mod.resize(n);
    inv_b.resize(n);
 
    inv_b[0] = cplx(1.0, 0.0) / b_;
    c_mod[0] = c_ * inv_b[0];
 
    for (int k = 1; k < n; ++k) {
        cplx bk  = b_ - a_coeff * c_mod[k - 1];
        inv_b[k] = cplx(1.0, 0.0) / bk;
        if (k < n - 1)
            c_mod[k] = c_ * inv_b[k];
    }
}
 
void ComplexTriDiag::solve(std::vector<cplx>& d) const {
    // Forward sweep
    d[0] *= inv_b[0];
    for (int k = 1; k < n; ++k)
        d[k] = (d[k] - a_coeff * d[k - 1]) * inv_b[k];
 
    // Back substitution
    for (int k = n - 2; k >= 0; --k)
        d[k] -= c_mod[k] * d[k + 1];
}
 
} // namespace num