Work out weaklaplacian(::DirichletPolynomial) for non-evenly spaced points

[dlfivefifty]

I think the only thing that's not trivial is the A block. The D blocks should just be changing step(r) to diff(r)

[dlfivefifty]

Note the A block is just standard FEM with hat functions. @ioannisPApapadopoulos do you know this off the top of your head?

[ioannisPApapadopoulos]

Yeah should be quite simply, something like -1/r for the off-diagonal and 1/r0 + 1/r1 for the main diagonal, where r0 and r1 are the interval lengths on the left and right hand side of the hats.

E.g. if a hat was scaled onto -1/2..0, 0..5, then the off diagonals are

(2 * -2)/2 = -2. = -1/r0 (left)
(-1/5 * 1/5)* 5 = -1/5 = =1/r1 (right).

the main diagonal is
(2*2)/2 + (-1/5 * -1/5)*5 = 2 + 1/5 = 1/r0 + 1/r1 = 11/5.

[dlfivefifty]

Ah ok so it’ll be something like 1 ./ diff(r)[1:end-1] + 1 ./ diff(r)[2:end] ? I think the dimensions match at least