This is the most commonly-used predation kernel. The log of the predator/prey mass ratio is normally distributed.

## Arguments

- ppmr
A vector of predator/prey size ratios

- beta
The preferred predator/prey size ratio

- sigma
The width parameter of the log-normal kernel

## Value

A vector giving the value of the predation kernel at each of the
predator/prey mass ratios in the `ppmr`

argument.

## Details

Writing the predator mass as \(w\) and the prey mass as \(w_p\),
the feeding kernel is given as
$$\phi_i(w, w_p) =
\exp \left[ \frac{-(\ln(w / w_p / \beta_i))^2}{2\sigma_i^2} \right]
$$
if \(w/w_p\) is larger than 1 and zero otherwise. Here \(\beta_i\) is the
preferred predator-prey mass ratio and \(\sigma_i\) determines the width of
the kernel. These two parameters need to be given in the species parameter
dataframe in the columns `beta`

and `sigma`

.

This function is called from `setPredKernel()`

to set up the
predation kernel slots in a MizerParams object.

## See also

Other predation kernel:
`box_pred_kernel()`

,
`power_law_pred_kernel()`

,
`truncated_lognormal_pred_kernel()`