# Eigen: divida cada fila de matriz (escasa) por su elemento diagonal correspondiente

Using the Eigen library in C++, given a sparse matrix `A`, what is the most efficient way (row-wise operations? how to?) to compute a sparse matrix `B` tal que `B(i, j) = A(i, j) / A(i, i)` ? That is, divide each row `i` by the corresponding diagonal element `A(i, i)`. It would be helpful to know how to do it both in-place (replacing entries in `A`) and out-of-place (creating a new sparse matrix `B`).

My sparse matrix is defined as:

``````typedef double Real;
typedef Eigen::SparseMatrix<Real> SparseMatrixR;
``````

Gracias,
m.

preguntado el 28 de mayo de 14 a las 13:05

## 1 Respuestas

In other words you want to extract the diagonal of A, view it as a diagonal matrix, and apply its inverse to A:

``````A = A.diagonal().asDiagonal().inverse() * A;
``````

This operation should be slightly more efficient if A is rowmajor.

contestado el 28 de mayo de 14 a las 13:05

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