Looking for DiffEQArrayOperator replacement

[ChrisRackauckas]

@cardoza2

        M = zeros(TF, nx, nx)
        update_mass_matrix! = (jacob, x, p, t) -> begin
            # zero out all mass matrix entries
            M .= 0.0
            # compute mass matrix
            mass_matrix!(jacob, x, p, (; constants..., t))
            # change sign of mass matrix
            M .*= -1
            # return result
            return M
        end

This piece of code is pretty suspect. Did you mean:

        update_mass_matrix! = (jacob, x, p, t) -> begin
            # zero out all mass matrix entries
            jacob .= 0.0
            # compute mass matrix
            mass_matrix!(jacob, x, p, (; constants..., t))
            # change sign of mass matrix
            jacob .*= -1
            # return result
            return jacob
        end

The previous version was relying on M and jacob having the same pointer, but that won’t necessarily always be the case.