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ptc-4484148
1-Newbie

This list contains too many items...

I created a function that contains a lot of variables. Apparently if the number of variables reaches 50, Mathcad does not allow additional variables to be added to the equation. It generates an error that states, "This list contains too many items." Is there a fix or workaround for this? I'm running Mathcad 14.0 M011. Thanks for any help you can provide.

6 REPLIES 6
RichardJ
19-Tanzanite
(To:ptc-4484148)

It's hard to imagine why you would want more than 50 independently named variables. If you name your variables, say, x1, x2, x3, etc, where the numbers a vector subscripts, then you can just put "x" in the functon's argument list. Then you can have as many variables as you want.

But what if I want to generate partial derivatives of the function (i.e. sensitivities) to find the extreme values? I’m not sure how to do this with vectors in the argument list.

RichardJ
19-Tanzanite
(To:ptc-4484148)

You need 50 partial derivatives?

I need to adjust each of the variables in one direction or the other to determine the extreme values (maximum and minimum) of the equation. This is typically done with partial derivatives or using some other method of perturbing each of the variables to determine which direction to take them. This is straightforward when each of the variables in the equation are explicitly listed, but when they are grouped in vectors the partial derivative function doesn’t recognize the vector subscripts.

RichardJ
19-Tanzanite
(To:ptc-4484148)

Would this approach work?

partial derivative.jpg

What kind of physical problem would involve more than 50 independent variables?

How would you know what the answer means? Even with only two variables, one can end up with a "saddle point" that appears to give a local minimum or maximum, but is not. This function is called "non analytic" in differential calculus.

How, then, do you know if your function is "analytic" in fifty or more dimensions?

Maybe you should reduce your problem to smaller chunks that are more manageable.


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