I’m trying to use DiffEqOperators to define the Kermack-McKendrick model, which is basically a PDE generalization of the simple SIR epidemiological model:

The equation for I is a PDE, while that for S and R is an ODE with an integral of I over a at t.

The declarations seem straightforward:

@parameters t a β γ @variables S(…) I(…) R(…) @derivatives Dt’~t @derivatives Da’~a

However, how does one describe integrals over one dimension (in this case, a)?

(missing out the boundary conditions and domains right now), to be passed to DiffEqOperators to be solved by the method of lines, along the lines of this:

This involves integrating along the spatial dimension rather than the time dimension - the latter is the issue you refer to for integro-differential equation support.

Yeah we can’t handle this in any of the discretizers right now. Lump it into the other requests. We’re getting to it, though a little slower than we hoped.