## 8.3 Sparse matrix arithmetic

### 8.3.1 Sparse matrix multiplication

The only supported operation is the multiplication of a sparse matrix $$A$$ and a dense vector $$b$$ to produce a dense vector $$A\,b$$. Multiplying a dense row vector $$b$$ and a sparse matrix $$A$$ can be coded using transposition as $b \, A = (A^{\top} \, b^{\top})^{\top},$ but care must be taken to represent $$A^{\top}$$ rather than $$A$$ as a sparse matrix.

vector csr_matrix_times_vector(int m, int n, vector w, array[] int v, array[] int u, vector b)
Multiply the $$\text{m} \times \text{n}$$ matrix represented by values w, column indices v, and row start indices u by the vector b; see compressed row storage.
Available since 2.18