subroutine std_dev_mn(y,n,ax,sig)
      real y(*)
      ax=0.
      sx=0.
      do i=1,n
         ax=ax+y(i)
      enddo
      ax=ax/n
      do i=1,n
         x=y(i)-ax
         sx=sx+x**2
      enddo
      sig=sqrt(sx/(n-1))
      return
      end