# NFW Potential

NFW potential of gNFW need the following parameters:
`x_centre`, `y_centre`, `ellipticite`, `angle_pos`, `alpha`, `scale_radius_kpc`, `concentration`, `z_lens` .


The Newtonian (spherical) gNFW potential is:

$$\Phi (x)  = \rho_S x^{-\alpha} (1 + x)^{- (3 - \alpha)}$$

where $x = r / r_S$ is a redimensionned radius (see [Limousin et al. 2008 eq. 1](https://ui.adsabs.harvard.edu/abs/2008A%26A...489...23L/abstract)).

$\alpha = 1.0$ corresponds to a regular NFW profile.


Example of lenstool NFW parametrisation:
```
potential  1
        profile              12
        x_centre             0.
        y_centre             0.
        ellipticity          0.
        angle_pos            0.
        alpha                1.
        scale_radius_kpc     30.
        concentration        5.5
        z_lens               0.2
        end
```

NOTE: If you want to use the generalized NFW profile, you need to prepare the lenstool.tab lookup table with this command:

```
make table 
```