code: public static boolean cs_gaxpy (DZcs A, DZcsa x, DZcsa y)
  	{
  		int p, j, n, Ap[], Ai[] ;
  		DZcsa Ax = new DZcsa() ;
  		if (!CS_CSC (A) || x == null || y == null) return (false) ;	/* check inputs */
  		n = A.n ; Ap = A.p ; Ai = A.i ; Ax.x = A.x ;
  		for (j = 0 ; j < n ; j++)
  		{
  			for (p = Ap [j] ; p < Ap [j+1] ; p++)
  			{
  				y.set(Ai [p], cs_cplus(y.get(Ai [p]), cs_cmult(Ax.get(p), x.get(j)))) ;
  			}
  		}
  		return (true) ;
  	}
docs: Sparse matrix times dense column vector, y = A*x+y.
  
  @param A
  column-compressed matrix
  @param x
  size n, vector x
  @param y
  size m, vector y
  @return true if successful, false on error