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Allow DESC to read wout files that lack lrfp logical (like VMEC++ files) #2014

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Merged
YigitElma merged 3 commits into from
Nov 13, 2025
Merged

Allow DESC to read wout files that lack lrfp logical (like VMEC++ files) #2014

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4ad2ded
allow DESC to read wout files that lack lrfp logical (like VMEC++ files)
dpanici Nov 13, 2025
ff1653f
update changelog
dpanici Nov 13, 2025
b96d3e6
Merge branch 'master' into dp/vmec-load
YigitElma Nov 13, 2025
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2 changes: 2 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -23,6 +23,8 @@ Bug Fixes
- Fixes inaccurate normalizations scales that could be computed for certain equilibria which had m=1 n=0 R and m=-1 n=0 Z components much smaller than their actual average minor radius, see [GH issue](https://github.com/PlasmaControl/DESC/issues/1954)
- [Fix bug in ``PlasmaCoilSetMinDistance`` that occured using a ``FourierRZToroidalSurface`` object without passing in an the evaluation grid](https://github.com/PlasmaControl/DESC/pull/2013)
- Equilibrium profile assignments are now guaranteed to be consistent with the equilibrium resolution—automatically increasing lower-resolution profiles to match the equilibrium (while keeping higher-resolution profiles untouched)—meaning users who relied on lower-resolution profiles to implicitly restrict optimization must now explicitly use the `FixParameters` constraint.
- Allow ``desc.vmec.VMECIO.load`` to load wout files that lack ``lrfp__logical__``, like those outputted by VMEC++. This change assumes that those output files don't have poloidal flux label.


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12 changes: 7 additions & 5 deletions desc/vmec.py
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Expand Up @@ -95,11 +95,13 @@
+ " while DESC is only designed for compatibility with VMEC version"
+ " 9. Some data may not be loaded correctly."
)

assert float(file.variables["lrfp__logical__"][0]) == 0, (
"DESC currently does not support poloidal flux label, "
"and so cannot load this VMEC wout, which has LRFP=T"
)
if "lrfp__logical__" in file.variables:

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# guard against the wout not having it, as VMEC++ does not save
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@YigitElma YigitElma Nov 13, 2025

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Does VMEC++ always output without poloidal flux label?

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@dpanici dpanici Nov 13, 2025

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yes for now at least https://github.com/proximafusion/vmecpp/blob/4f41149a01e8a43affcdb83bebb82c47b2a9a8a7/tests/test_init.py#L165

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@jonathanschilling jonathanschilling Nov 13, 2025

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Ahh yeah, sorry for the inconsistency. I hope it is not too inconvenient for you guys to have to work around that. We probably should add these wout variables to VMEC++, even if they would just be static values, as in the case of lrfp__logical__. Or maybe we'll even see a PR adding these some time 🤞 ?

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@YigitElma YigitElma Nov 13, 2025

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Thanks for the reply @jonathanschilling ! I think the current workaround is fine (as long as a user gives an output with poloidal flux label that doesn't have this attribute).

# all the flags that VMEC does
assert float(file.variables["lrfp__logical__"][0]) == 0, (

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"DESC currently does not support poloidal flux label, "
"and so cannot load this VMEC wout, which has LRFP=T"
)

# parameters
inputs["Psi"] = float(file.variables["phi"][-1])
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