Retuen the number of non-zero values of the specified submatrix of a given sparse matrix rapidly

1 |

`m` |
The matrix |

`rows` |
The integer vector of row index(es) or logical vector indicated the selected rows |

`cols` |
The integer vector of column index(es) or logical vector indicated the selected cols |

This function implements faster calculation algorithm for the
`CsparseMatrix`

and `RsparseMatrix`

class in the package Matrix.

This function will return the number of non-zero values in the specified submatrix.

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