Add a function mechInfo() to return compiled mechanism information

[blttkgl]

Hey,

We use pyJac with linking it to OpenFOAM as a dynamic library through case folders. During compiling the OpenFOAM chemistry model we use dummy pyjac headers, since we want to be able to use different mechanisms via pyJac by linking the appropriate dynamic library from the case folder.

At the moment there is no easy way to check if the mechanism input file provided and mechanism pyJac is compiled and dynamically linked are matching. Since header files are dummy (so we are not limited to one mechanism), we can't for instance check number of species NSP, since it is #defined in the mechanism.h.

Would you be able to add a get_mech_info() function, which returns the mechanism information such as number of species, number of variables, forward reactions etc. when called? If this is implemented it enables OpenFOAM users to use multiple mechanisms without re-compiling their models, by simply checking e.g. pyJac mechanism size matches the mechanism they want to use.

I can also try to provide this change and open a pull request if you are interested.

Thanks!

Bulut

[kyleniemeyer]

Hi @blttkgl, thanks for your interest! I/we aren't actively developing pyJac at this time, but I'd be happy to look at a pull request.

However, I am a bit confused about

If this is implemented it enables OpenFOAM users to use multiple mechanisms without re-compiling their models, by simply checking e.g. pyJac mechanism size matches the mechanism they want to use.

Is the idea that you have compiled OpenFOAM for a particular model size, but could vary the chemistry model by only updating the output from pyJac, without recompiling everything else?

[blttkgl]

Hey @kyleniemeyer !

Yes, that's correct. We link the header files of a (any) pyJac output to our chemistryModel, so that the pyJac functions are defined during model compilation via headers. During usage, we link the libc_pyjac.so library dynamically to our solver, so OpenFOAM uses the pyJac output of the chemical mechanism we want to use. I implemented a check at the constructor of OpenFOAM side that checks the number of species of the pyJac mechanism linked with the number of species that the user provided via an input file to OpenFOAM by implementing two functions in chem_utils.c of pyJac, PYJAC_NSP() and PYJAC_FWD_RATES():

    if (this->nSpecie_ == PYJAC_NSP())
    {
        Info<<"Mechanism information:\n"<<"Number of species: "<<PYJAC_NSP()<<"\n"
        <<"Number of reactions: "<<PYJAC_FWD_RATES()<<endl;
    }
    else
    {
        FatalErrorIn
        (
            "pyJacLoadBalancedChemistryModel"
        ) 
    }

I can't call NSP and FWD_RATES directly because they are defined as preprocessor directives. I would just return the output from the dummy pyJac output I compiled my model with. At the moment I add these functions to chem_utils.c and chem_utils.h with some bash scripting when I create new pyJac output:

int PYJAC_NSP()
{
    return NSP;
}
int PYJAC_FWD_RATES()
{
    return FWD_RATES;
}

We will be making our source code public and have pyJac-v1 as a dependency. It would be nice if pyJac generated these functions natively when the user installs it as a python submodule via pip (we want users to use it as submodule only, not compile the pyJac from source code). Of course if updating the code and the python submodule is a task you do not have time to spare, I can either try to create a patch for you or simply stick to my bash scripting magic :)

Best,

Bulut