= Memory kernel
{title2=$(\kappa*v)(t)=\int_0^t\kappa(u)v(t-u)\,du$}
A function weighting the influence of past values in a history-dependent equation. In a <Volterra integral equation> its <convolution> with the history is causal: only earlier times appear. For an integrable kernel, $\widetilde\kappa(0)=\int_0^\infty\kappa(u)\,du$ measures its response to a constant input. In a <generalized Langevin equation>, the friction <memory kernel> records delayed resistance to the <velocity>.
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