# Changing mesh name from Th to Th3 appears to generate problems
**URL:** https://community.freefem.org/t/changing-mesh-name-from-th-to-th3-appears-to-generate-problems/2364
**Category:** General Discussion
**Created:** [March 30, 2023, 10:55am UTC](https://community.freefem.org/t/changing-mesh-name-from-th-to-th3-appears-to-generate-problems/2364 "2023-03-30T10:55:03Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@marchywka](https://community.freefem.org/u/marchywka)
#### Post date: [March 30, 2023, 10:55am UTC](https://community.freefem.org/t/changing-mesh-name-from-th-to-th3-appears-to-generate-problems/2364/1 "2023-03-30T10:55:03Z")
Iām trying to convert some code to use PETSc. I tried to copy an example but got
various compile errors and then seg faults at run time. I isolated a problem upstream
but have not verified to is a problem later. At issue seems tobe the name of the mesh and
requirement for macro defs that are suspcious later on. For example, the two attached files
differ only in Th vs Th3 for the mesh name but Th3 fails at compile without the defs for def and
init lol. What is the deal here? Am I missing something simple? Thanks.
[mwe\_defs3.edp](https://community.freefem.org/uploads/short-url/aNuQNZ21dd7IXhtwBGj9FjUm22x.edp) (1.6 KB)
[mwe\_defs.edp](https://community.freefem.org/uploads/short-url/7SDBcTZg779dAyoaaGUKC3hmHhI.edp) (1.5 KB)
```auto
diff mwe*
32c32
< mesh3 Th3 = cube(Xpts,Ypts,Tpts);
---
> mesh3 Th = cube(Xpts,Ypts,Tpts);
34c34
< Th3=change(Th3,refface=chlab);
---
> Th=change(Th,refface=chlab);
39c39
< buildDmesh(Th3)
---
> buildDmesh(Th)
41d40
< // need to uncomment naming mesh Th3 and then it bombs during run ???
46c45
< createMat(Th3, AP, Pk)
---
> createMat(Th, AP, Pk)
```
```auto
4967 ff-mpirun -np 1 mwe_defs.edp -wg
4968 vi mwe_defs.edp
4969 cp mwe_defs.edp mwe_defs3.edp
4970 vi mwe_defs3.edp
4971 ff-mpirun -np 1 mwe_defs3.edp -wg
```
---
### Author:  [@marchywka](https://community.freefem.org/u/marchywka)
#### Post date: [March 30, 2023, 12:44pm UTC](https://community.freefem.org/t/changing-mesh-name-from-th-to-th3-appears-to-generate-problems/2364/2 "2023-03-30T12:44:07Z")
I went back and changed the full code and it now appears to run although the solution
is not correct it no longer seg faults and I dont need the macro defs for def and init š
I have a bunch of little issues like this that take forever to track down but now I want
to get the results and see if the math/analysis makes any sense. I had to scale down to
a 2+1D electrmagnetics problem with the z dimension as time. Iām using the last result
for the initial conditions of a new solve so I have some more detais
to check.
---
### Author:  [@henkel](https://community.freefem.org/u/henkel)
#### Post date: [March 30, 2023, 3:02pm UTC](https://community.freefem.org/t/changing-mesh-name-from-th-to-th3-appears-to-generate-problems/2364/3 "2023-03-30T15:02:20Z")
You neglected to update the name of the mesh in the macro definitions. Change `ThN2O` to `Th3N2O` and `ThPkPart` to `Th3PkPart`.
---
### Author:  [@marchywka](https://community.freefem.org/u/marchywka)
#### Post date: [March 30, 2023, 4:23pm UTC](https://community.freefem.org/t/changing-mesh-name-from-th-to-th3-appears-to-generate-problems/2364/4 "2023-03-30T16:23:23Z")
Thanks. Iām kind of curious what kind of code it generated now š I guess it was easy to
overlook as I would expect a compile time error. The scoped macro idea, kind of
like c++ templates, is powerful but apparently takes dome getitng used to.