Error in DerivedVariable Definition with curl Function in derived_merged Branch

[hxu65]

Description:
When executing the gray_scott simulation using the hermes_derived engine or bp5_derived engine in the derived_merged branch, the program terminates unexpectedly due to a std::out_of_range exception. This issue arises specifically when using the curl function in the Adios2 repo "source/adios2/toolkit/derived/parser/lexer.l".

ADIOS2 DefineDerivedVariable definition:

#ifdef ADIOS2_HAVE_DERIVED_VARIABLE
VariableDerived IO::DefineDerivedVariable(const std::string &name, const std::string &expression,
                                          const DerivedVarType varType)
{
    helper::CheckForNullptr(m_IO,
                            "for variable name " + name + ", in call to IO::DefineDerivedVariable");

    return VariableDerived(&m_IO->DefineDerivedVariable(name, expression, varType));
}

we run adios with derived quantities defined like this:

auto PDFU = io.DefineDerivedVariable("derive/pdfU",
                                             "x:U \n"
                                             "curl(10, x)",
                                             adios2::DerivedVarType::StoreData);
auto PDFV = io.DefineDerivedVariable("derive/pdfV",
                                             "x:V \n"
                                             "curl(10, x)",
                                             adios2::DerivedVarType::StoreData);

Steps to Reproduce:
Checkout the derived_merged branch.
Run the gray_scott simulation with either the hermes_derived or bp5_derived engine.
Observe the program termination and error message:

terminate called after throwing an instance of 'std::out_of_range'
what(): map::at

The error occurs at: writer.cpp#L101, when defining DerivedVariable with curl(10,x).

Expected Behavior:
The program should execute without errors, allowing DerivedVariable definitions with the curl function.

Actual Behavior:
The program terminates with a std::out_of_range exception when a DerivedVariable is defined using the curl function.

Environment Details:
ADIOS2: ADIOS2@master with derived enable in spack
Hermes: Hermes@master
Branch: derived_merged
Engines: hermes_derived, bp5_derived
File/Code Reference: writer.cpp#L101

Potential Solution/Workaround:

1. Modify the DerivedVariable definition to use the magnitude function instead of curl bypasses the issue, suggesting the problem lies with the curl function handling. Example workaround:

auto PDFU = io.DefineDerivedVariable("pdfU",
                                     "x:U \n"
                                     "magnitude(x)",
                                     adios2::DerivedVarType::StoreData);
auto PDFV = io.DefineDerivedVariable("pdfV",
                                     "x:V \n"
                                     "magnitude(x)",
                                     adios2::DerivedVarType::StoreData);

2. add function definition in adios2 repo: /source/adios2/toolkit/derived/Function.h