Creates a new matrix object that behaves like A + U*C*V'
PetscErrorCode MatCreateLRC(Mat A,Mat U,Vec c,Mat V,Mat *N)
Collective on Mat
|A ||- the (sparse) matrix (can be NULL)
|U, V ||- two dense rectangular (tall and skinny) matrices
|c ||- a sequential vector containing the diagonal of C (can be NULL)
N -the matrix that represents A + U*C*V'
The matrix A + U*C*V' is not formed! Rather the new matrix
object performs the matrix-vector product by first multiplying by
A and then adding the other term.
C is a diagonal matrix (represented as a vector) of order k,
where k is the number of columns of both U and V.
If A is NULL then the new object behaves like a low-rank matrix U*C*V'.
Use V=U (or V=NULL) for a symmetric low-rank correction, A + U*C*U'.
If c is NULL then the low-rank correction is just U*V'.
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