anchor.diff:        
   !     x <- sig ^-1 * x
         call DPOTRS('L',n,1,sig,n,x,n,info)
  +
  +      gd=0.0D0
  +      do i=1,n
  +          gd=gd+x(i)*mu(i)
  +      end do
         
   !     like <- .5 dot(x,mu) (.5 (x-mu) C^{-1} (x-mu)^T)
  -      like = -0.5D0 * DDOT(n, x, 1, mu, 1)
  +      like = -0.5D0 * gd
   !       print *, like
         
         twopi_N = 0.5D0 * N * dlog(2.0D0*PI)
  
positive.code: ! DAXPY(N,DA,DX,INCX,DY,INCY) Adding vectors
        EXTERNAL DCOPY
  ! DCOPY(N,DX,INCX,DY,INCY) copies x to y
        EXTERNAL DDOT
        
  !     x <- (x-mu)      
        call DAXPY(n, -1.0D0, mu, 1, x, 1)
  
negative.code: ! DAXPY(N,DA,DX,INCX,DY,INCY) Adding vectors
        EXTERNAL DCOPY
  ! DCOPY(N,DX,INCX,DY,INCY) copies x to y
  
        twopi_N = 0.5D0 * N * dlog(2.0D0*PI)
  
  