interface SparseMatrixData {
    _size: number[];
    _values?: unknown[];
    _index: number[];
    _ptr: number[];
}
/**
 * Keeps entries in the matrix when the callback function returns true, removes the entry otherwise
 *
 * @param {Matrix}   a              The sparse matrix
 * @param {function} callback       The callback function, function will be invoked with the following args:
 *                                    - The entry row
 *                                    - The entry column
 *                                    - The entry value
 *                                    - The state parameter
 * @param {any}      other          The state
 *
 * @return                          The number of nonzero elements in the matrix
 */
export declare function csFkeep<T, S = unknown>(a: SparseMatrixData, callback: (row: number, col: number, value: T, state: S) => boolean, other: S): number;
export {};
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