Dynamic modelling

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Dynamic modelling in ASCEND is where you solve a system of ordinary differential equations (ODEs) or differential/algebraic equations for the time-varying values of variables in the model over a certain interval, given the initial conditions of the model. We also refer to this as integration. Dynamic modelling can be done within the ASCEND language providing the relationship between variables and their derivatives can be established.

The current method for specifying derivatives is by including the ivpsystem.a4l library:

REQUIRE "ivpsystem.a4l";

at the start of your model, then creating a special method

METHOD ode_init;
    dx_dt.ode_id := 1;
    x.ode_id := 1; (* ie these variables are related with ID '1' *)

    dx_dt.ode_type := 2; (* ie 'this is a derivative variable' *)
    x.ode_type := 1; (* ie 'this is a differential variable *)
END ode_init;