5.4 MXVB: matrix-vector product

      subroutine mxvb(a,mcola,mrowa,b,mcolb,
     1                r,mcolr,ncol,nlink)
      implicit double precision (a-h,o-z)
      dimension r(1),a(1),b(1)

calculates the ${\tt ncol}\times{\tt nrow}$ matrix product $\bf r = r + A b$. Parameters are exactly as for mxva; the only difference is that r is not cleared to zero at the start, but the matrix product is added to the previous contents of r.