c     product of two general double precision matrices.
      subroutine dgmprd (a,b,r,n,m,l)
      double precision a(1), b(1), r(1)
      ir=0
      ik=-m
      do 10 k=1,l
      ik=ik+m
      do 10 j=1,n
      ir=ir+1
      ji=j-n
      ib=ik
      r(ir)=0
      do 10 i=1,m
      ji=ji+n
      ib=ib+1
   10 r(ir)=r(ir)+a(ji)*b(ib)
      return
      end