lis

The lis solver supports the following input types.

• data type: D (double only)
• index type: std::int32_t, std::int64_t

lis is an iterative solver from the Lis library. It requires a matrix in zero-based CSR (Compressed Sparse Row) format.

Constructor

The constructor accepts an optional string of solver options (see Solver Options below).

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auto solver = lis("-i fgmres -p ilu");

Input Format

The matrix \(A\) must be provided as a sparse_csr_mat with zero-based indexing. Fields required:

• n — number of rows (and columns) of the square matrix,
• nnz — number of non-zero entries,
• row_ptr — array of length n+1, where row_ptr[i] is the index of the first non-zero in row i,
• col_idx — array of length nnz, column indices of the non-zero entries,
• data — array of length nnz, values of the non-zero entries.

The right-hand side \(B\) is a dense full_mat with n_rows = N and n_cols = NRHS.

Usage Example

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#include <ezp/lis.hpp>

using namespace ezp;

int N = 10, NRHS = 1;
std::vector<int_t> ia, ja;
std::vector<double> a, b;

// populate zero-based CSR diagonal matrix on root process
if(0 == mpl::environment::comm_world().rank()) {
    ia.resize(N + 1);  ja.resize(N);  a.resize(N);  b.resize(N * NRHS);
    for(auto i = 0; i < N; i++) { ia[i] = ja[i] = i; a[i] = i + 1; }
    ia[N] = N;
    std::ranges::fill(b, 1.);
}

auto solver = lis("-print all -p ilu -ilu_fill 1 -i fgmres");
const auto info = solver.solve({N, N, ia.data(), ja.data(), a.data()}, {N, NRHS, b.data()});

Solver Options

Call the set_option method to change solver options after construction.

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solver.set_option("-i fgmres -p ilu -print 2");

All available options are documented in the official Lis documentation. Commonly used options include: