The farther away an electron is from the point of origin the hotter it will be. If it reflects off something and approaches the point of origin it will get colder again.

function test_update(i, x, y, s, n)
if tpt.get_property("tmp",i) == 0 then
tpt.parts[i].tmp=x
tpt.parts[i].tmp2=y
end
ix=tpt.get_property("tmp",i)
iy=tpt.get_property("tmp2",i)
tpt.parts[i].temp=20*math.sqrt((x-ix)^2 +(y-iy)^2)
end
tpt.element_func(test_update, tpt.el.elec.id)