      subroutine matmul(x,y,z)
      real*8 x(4),y(4),z(4)
c
c
      z(1)=x(1)*y(1)+x(2)*y(3)
      z(2)=x(1)*y(2)+x(2)*y(4)
      z(3)=x(3)*y(1)+x(4)*y(3)
      z(4)=x(3)*y(2)+x(4)*y(4)
c
      return
      end
