Q: How can I calculate the derivative of a compartmental mass?

A: In the Equation window, the differential equations are available for the model. For example, for the example two-compartment model in study_0.stu, the following differential equations can be viewed by opening the Equation Window and selecting "Diff. Eq." from the "View" menu:

q1' = + k(1,2)*q2 - k(2,1)*q1 - k(0,1)*q1+ ex1

q2' = - k(1,2)*q2 + k(2,1)*q1  

where q1 and q2are the masses in compartment 1 and 2 respectively. The derivative with respect to time of q1, for example, is given by the expression + k(1,2)*q2- k(2,1)*q1 - k(0,1)*q1 + ex1, which can be easily calculated off-line, by simply writing in the Equation Window and then plotting an expression like:

derivative = + k(1,2)*q2 - k(2,1)*q1 -k(0,1)*q1 + ex1

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