Hi,

I am trying to read a value usign external function and assign it to a variable to be used in a derivative equation. I am getting the following error

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"Error: Derivative of expression Functions.Psat_T(T_l) is non-existent

Here is a part of the code that is causing the error

Q_total = m_l * C * T_l + m_v * (C * T_l + lat_heat) + m_t * C_m * T_m - P_v * V;

P_v = Functions.Psat_T(T_l);

der(Q_total) = Q_in + W_in * h_w - W_out * (C * T_l + lat_heat);

I am trying to get values for P_v from the function so the equations can be solved.

Please let me know if there is any option to read the values from functions and assign it to the variable to be used in the equation,

Thanks and Regards

John