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Is it possible to call a function in GCON which is implemented as user written subroutine in C++

WWitteve
GCON forces a function to be zero. Is it possible to call such a function which is implemented as user written subroutine in C. If yes, is there an example available?
Thanks in advance,
Wolfgang Witteveen
 
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    What I tried in the past was creating a solver variable that was using DM(i,j) and a GCON refering to varval(var). That worked fine.
     
    If the var is a usersub, I'd expect the solver needs to know about the dependencies. In good old Fortran that was done by calling things like SYSFNC when IFLAG being TRUE.
    I don't know how a c-code handles that, but I assume that it works the same way.
     
    In <topdir>/solver/c_usersubs/varsub.c you'll find an example that you can try.
    If you modify it to always return DZ(par(1), Par(2))-20, then I'd expect a GCON with varval(var) should keep the marker distance in Z to 20.
     
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    Hi Wolfgang,
     
    Accessing a state variable defined by a user-written subroutine (VARSUB) is not supported in a GCON. From the solver documentation:
     
    The ability of the Adams Solver (C++) to handle function expressions to provide the necessary derivatives required by the GCON does not extend to user subroutines. Consequently, a VARIABLE can only be referenced in a GCON provided it is defined using function expressions, rather than a VARSUB subroutine.
     
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