encounter_kernel: The predation kernel as used by the encounter quadrature

In mizer: Dynamic Multi-Species Size Spectrum Modelling

The predation kernel as used by the encounter quadrature

Description

Returns the kernel array \Phi_i(w_k, w_p) for which

E_i(w_k) = \gamma_i(w_k) \sum_p \Phi_i(w_k, w_p) N^{eff}_i(w_p) w_p \Delta w_p

reproduces exactly the available energy computed by mizerEncounter(), where N^{eff} is the interaction-weighted prey density. It is the kernel that any summary function must use if its result is to be consistent with getEncounter().

Usage

encounter_kernel(params)

Arguments

params

A MizerParams object.

Details

On the default first-order path this is just the point-sampled kernel returned by pred_kernel(). When second-order bin-averaging is switched on (see second_order_w()) the two differ: setPredKernel() then builds the Fourier-transformed kernel from the kernel integrated over the prey bin, divided by \beta - 1 so that the plain point weight w_p \Delta w_p carried by the prey vector is cancelled. Those bin-integrated weights are recovered here from params@ft_pred_kernel_e by an inverse Fourier transform, which costs one FFT and keeps this helper automatically in step with whatever quadrature setPredKernel() used.

Pair it with the plain point prey weight params@w_full * params@dw_full. That weight is a normalisation which the kernel construction is built to cancel, not a first-order quadrature weight, so it must not be passed through bin_average_weight(): doing so applies the prey-bin integral twice. A summary function that instead pairs the point-sampled pred_kernel() with a bin-averaged prey weight double-counts that quadrature; that was the bug behind issue #474.

Value

An array (predator species x predator size x prey size).

See Also

pred_kernel() for the point-sampled kernel used for plotting and for supplying a custom kernel, second_order_w(), bin_average_weight()

mizer documentation built on Aug. 31, 2026, 5:08 p.m.