docs: public static void multRows(double[] diag, int offset, DMatrixSparseCSC A) {
          if( diag.length < A.numRows )
              throw new IllegalArgumentException("Array is too small. "+diag.length+" < "+A.numCols);
  
          for (int i = 0; i < A.nz_length; i++) {
              A.nz_values[i] *= diag[A.nz_rows[i+offset]];
          }
      }