Duhamel principle (source code)

= Duhamel principle
{c}
{wiki=Duhamel's_principle}

For a linear evolution equation with zero initial data, Duhamel's principle integrates the homogeneous propagator against the forcing time. For the forced heat equation,
$$
u(x,t)=\int_0^t\int_{-\infty}^{\infty}
K_{t-\tau}(x-\xi)f(\xi,\tau)\,d\xi\,d\tau.
$$