Result nodal_moment shown as unavailable for mapdl::rst

[PProfizi]

Before submitting the issue

• I have checked for Compatibility issues
• I have searched among the existing issues
• I am using a Python virtual environment

Description of the bug

The source operator nodal_moment is exposed (operator M), but its counterpart for mapdl::rst::M appears not to exist.

We need to either expose it properly or document for which namespaces (file types) this result is indeed available (PS: I have not found any implementation of M for any namespace).

Steps To Reproduce

With all the latest dev versions

Input

import ansys.dpf.core as dpf

print(dpf.start_local_server())


from ansys.dpf.core import examples

ds = dpf.DataSources(examples.find_static_rst())

op = dpf.operators.result.nodal_moment(data_sources=ds)
print(op)
print(op.eval())

Output

Traceback (most recent call last):
  File "D:\ANSYSDev\Sandbox\pydpf-core\Issues\MAPDL\nodal_moment.py", line 12, in <module>
    print(op.eval())
          ^^^^^^^^^
  File "D:\ANSYSDev\Sandbox\pydpf-core\src\ansys\dpf\core\dpf_operator.py", line 810, in eval
    return self.outputs._outputs[0]()
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\ANSYSDev\Sandbox\pydpf-core\src\ansys\dpf\core\outputs.py", line 102, in __call__
    return self.get_data()
           ^^^^^^^^^^^^^^^
  File "D:\ANSYSDev\Sandbox\pydpf-core\src\ansys\dpf\core\outputs.py", line 81, in get_data
    output = self._operator.get_output(self._pin, type_output)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\ANSYSDev\Sandbox\pydpf-core\src\ansys\dpf\core\dpf_operator.py", line 592, in get_output
    internal_obj = type_tuple[1](self, pin)
                   ^^^^^^^^^^^^^^^^^^^^^^^^
  File "D:\ANSYSDev\Sandbox\pydpf-core\src\ansys\dpf\gate\generated\operator_capi.py", line 422, in operator_getoutput_fields_container
    raise errors.DPFServerException(sError.value)
ansys.dpf.gate.errors.DPFServerException: M:0<-Source operator "mapdl::rst::M" not found

Which Operating System causes the issue?

Windows, Linux, MacOS

Which DPF/Ansys version are you using?

DPF Server 2025.2.pre0

Which Python version causes the issue?

3.12

Installed packages

NA

[PProfizi]

Hi @ricardopeixotocoelho @oparreno, the nodal moment operator M is among the CommonResultDefs.
Is that an error or does mapdl::rst::M really not exist? Is it something else?

[ricardopeixotocoelho]

Hi @PProfizi. In fact, mapdl::rst::M doesn't exist. There is a SourceOperator M so I guess it should exist for another file type but I can't find anything either.
@oparreno Do you know if there is an operator Moment for other file types ? Or can we delete this SourceOperator ?

[oparreno]

@PProfizi, there is no operator for nodal moments since MAPDL does not have such record. This is actually a similar case to the "F" operator @ricardopeixotocoelho is modifying for RF. Users should use element_nodal_forces or force_summation operators to get nodal forces/moments from the elemental_nodal records.

[PProfizi]

Thanks @oparreno @ricardopeixotocoelho, that confirms it then.

One possibility though I wanted to discuss with you, since this operator is exposed and frequently requested by users (to get moments by themselves), do you think it would be possible to still implement a mapdl::rst::M operator, which would reconstruct the field of moments for the user?
I think that until now source operators have had a 1 to 1 equivalence with results available directly in the RST, but you could think of this one more like a helper. And since the logic to rebuild it would be specific to RST, it would make sense to implement it as mapdl::rst::M. What do you think?
That would mean switching this to a feature request.

[oparreno]

@PProfizi, I'm not convinced that creating an operator that does that transformation for all the scoping in MAPDL is the way to go about this.
On the MAPDL side, typically users would use FSUM, NFORCE commands. These commands will take the current nodal scoping (NSEL) and current elemental scoping (ESEL) and average ENFs from the elemental scoping on the nodal scoping. Our current Source Operators only support one single scoping. We created the operator "force_summation" to allow to pass two scopings and have similar post-processing capabilities as FSUM & NFORCE (it also will handle accumulation and moment calculations accounting for forces on the specified point).
cc. @ricardopeixotocoelho @ecottanceau