subroutine simul(a,b,x,n)
	dimension a(4,4),b(4),x(4),ainv(4,4),wkarea(4)
	ia=n
	idgt=n
	call linv1f(a,n,ia,ainv,idgt,wkarea,ier)
	do i=1,n
	   x(i)=0.0
	  do j=1,n
	    x(i)=ainv(i,j)*b(j)+x(i)
	    end do
	  end do
	return
	end