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How do I get MathCAD to solve sets of differential equations with circular equation definitions?

By expanding the equations to the below, I managed to get Mathcad to solve it.

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But I'd really like to be able to have MathCAD solve the original set of equations as shown below. As you can see, it's complaining that the red-boxed functions are undefined. The specific error message is "This variable is undefined. Check that the label is set correctly."

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I'm honestly impressed that MathCAD can solve the expanded of equations which are still circular, but I'm confused why it won't accept the second, unexpanded set.

Arely Torres
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  • I don't see what you call here "circular" functions ? – Jean Marie Sep 01 '21 at 04:28
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    Circular definitions are when two or more equations/functions reference each other in their definitions/values. For example: Fa(V) is defined in terms of Ca(V) but Ca(V) is defined in terms of Fa(V). This is an issue since it means you can't just define one of them first like you would if they didn't both reference each other. How do you order these two functions so that MathCad is happy? Do you put in Fa(V)=-k(v)*Ca(V) first or Ca(V)=Fa(V)/v(V) ? – Arely Torres Sep 01 '21 at 08:12
  • I had misunderstood the use of adjective "circular" (I thought to circular function as being $\cos, \sin,...$ etc. !). – Jean Marie Sep 02 '21 at 10:08

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