code: public static boolean cs_gaxpy(Scs A, float[] x, float[] y) {
          int p, j, n, Ap[], Ai[];
          float Ax[];
          if (!Scs_util.CS_CSC(A) || x == null || y == null)
              return (false); /* check inputs */
          n = A.n;
          Ap = A.p;
          Ai = A.i;
          Ax = A.x;
          for (j = 0; j < n; j++) {
              for (p = Ap[j]; p < Ap[j + 1]; p++) {
                  y[Ai[p]] += Ax[p] * x[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