SparseMatrix: Setting an element to zero, suppresses all nonzeros which do not satisfy the predicate

Suppose you already have a sparse matrix A that you already used for some purpose like solving Ax=b, and now you would like to change a *few* entries in A, and in particular to remove some? If that’s so, then set them to 0 using A.coeffRef(i,j) = 0, and once you’re done, you can remove them with A.prune(0, 1e-8).

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