code: public static void mult(DMatrixSparseCSC A ,
                              double b[] , int offsetB ,
                              double c[] , int offsetC )
      {
          Arrays.fill(c,offsetC,offsetC+A.numRows,0);
          multAdd(A,b,offsetB,c,offsetC);
      }
docs: c = A*b
  
  @param A (Input) Matrix
  @param b (Input) vector
  @param offsetB (Input) first index in vector b
  @param c (Output) vector
  @param offsetC (Output) first index in vector c