# NDSolveValue -difference between Version 11.2 and Version 11.3

I am trying to learn something about simulation of heat transfer by looking at this problem which is an answer by user21. If I try this in Version 11.3 the following happens:

$VersionNumber  11.3 Needs["NDSolveFEM"] tdiff[z_] := 0.5 + 0.1 UnitStep[z - 1] + 0.2 UnitStep[z - 2]; eqn = tdiff[z]*D[u[t, r, z],t] - (D[u[t, r, z], z, z] + (1/r) D[r D[u[t, r, z], r], r]); Ω = ImplicitRegion[True, {{r, 0.001, 200}, {z, 0, 3}}]; sol = NDSolveValue[{ eqn == NeumannValue[30 - u[t, r, z], z == 0], DirichletCondition[u[t, r, z] == 35, z == 3], DirichletCondition[u[t, r, z] == 0, r == 200], u[0, r, z] == 0}, u, {t, 0, 1000}, {r, z} ∈ Ω]  There are error messages related to NDSolveValue the first of which is: However, if I repeat the above in $VersionNumber


11.2

I do get a solution.

Which I can plot as

   Animate[Plot3D[sol[t, r, z], {r, z} ∈ Ω,
PlotRange -> {All, All, {0, 35}}], {t, 0, 5}]


Is there something changed in version 11.3?

• Workaround,with this: \[CapitalOmega] = ImplicitRegion[True, {{r, 1/1000, 200}, {z, 0, 3}}]; works. – Mariusz Iwaniuk Nov 8 '18 at 13:32

As a quick fix you could use generate the mesh with ToElementMesh first:

mesh = ToElementMesh[\[CapitalOmega], RegionBounds[\[CapitalOmega]]]
sol = NDSolveValue[{eqn == NeumannValue[30 - u[t, r, z], z == 0],
DirichletCondition[u[t, r, z] == 35, z == 3],
DirichletCondition[u[t, r, z] == 0, r == 200], u[0, r, z] == 0},
u, {t, 0, 1000}, {r, z} \[Element] mesh]


or, as suggested in a comment use an exact region representation in your original code:

\[CapitalOmega] = ImplicitRegion[True, {{r, 1/1000, 200}, {z, 0, 3}}];


I'd need to look a bit closer to see what is going on in your case. Sorry about that.

These two function calls should return the same but they do not and that is a bug I'll report:

RegionMeshBoundariesToBoundaryMeshRegion[{0.001 - x <=
0 && -200 + x <= 0 && -y <= 0 && -3 + y <= 0}, {x, 1/1000,
200}, {y, 0, 3}]


and

RegionMeshBoundariesToBoundaryMeshRegion[{1/1000 - x <= 0 && -200 + x <= 0 && -y <= 0 && -3 + y <= 0}, {x, 1/1000, 200}, {y, 0, 3}]

• Thanks, got me going again as usual. – Hugh Nov 9 '18 at 12:20
• @Hugh, glad I could help. The fix for the code should make it into the sources today and then a next release will have the fix for you. Sorry for the trouble and thanks for reporting. – user21 Nov 9 '18 at 12:43