anchor.diff:  cf2py double precision dimension(n,n), intent(copy) :: tau
   cf2py double precision intent(out) :: like
   
  -      DOUBLE PRECISION tau(n,n), x(n), mu(n), like
  -      INTEGER n, info
  +      DOUBLE PRECISION tau(n,n), x(n), mu(n), like, gd
  +      INTEGER n, info, i
         DOUBLE PRECISION infinity
         PARAMETER (infinity = 1.7976931348623157d308)      
         DOUBLE PRECISION 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: !     mu <- tau * x
        call DSYMV('L',n,1.0D0,tau,n,x,1,0.0D0,mu,1)
  
        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 * gd
  
  !      Cholesky factorize tau for the determinant.      
         call DPOTRF( 'L', n, tau, n, info )
  