# skfolio.utils.stats.symmetrize ### skfolio.utils.stats.symmetrize(matrix, where=None) In-place symmetrization: $M \leftarrow (M + M^T) / 2$. When `where` is provided, only the sub-block indexed by the mask is symmetrized, leaving the rest of the matrix untouched. This is useful for matrices that contain NaN rows/columns where a full transpose would propagate NaNs into the finite block. * **Parameters:** **matrix** *ndarray of shape (n, n)* : Square matrix to symmetrize in-place. **where** *ndarray of shape (n,), optional* : Boolean mask indicating which rows/columns to include. If `None`, the full matrix is symmetrized.