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Anousheh1-Visitor
1-Visitor
February 10, 2013
Solved

Symbolic Derivative Problem

  • February 10, 2013
  • 1 reply
  • 4055 views

Hello,

Please see the attached worksheet.

I need the actual derivative of vf(lambda,alpha) function. MathCad says it is too long to be shown.

Is there any way to overcome this issue?

Thank you so much.

Anousheh

Best answer by Werner_E

Anousheh Rouzbehani schrieb:

Hello,

Please see the attached worksheet.

I need the actual derivative of vf(lambda,alpha) function. MathCad says it is too long to be shown.

Where? I couldn't find that problem in you worksheet. Obviously I'm missing the point. Always better to post a stripped down worksheets which just shows the error or, as in your case, the undesired behaviour.

As you have defined Alpha at the top I assume you are interested in the derivative wrt lamda. I move the range variable for lamda down a bit.

cohesive2.png

One way to look at an expression which Mathcad 15 says being to long is to convert the worksheet in Prime format and load it in Prime 2, if you have the possibility to do so. Prime would let you scroll - no, unfortunately not, but you are allowed to enlarge the expression region to the right.

1 reply

W
Werner_E25-Diamond IAnswer
25-Diamond I
February 10, 2013

Anousheh Rouzbehani schrieb:

Hello,

Please see the attached worksheet.

I need the actual derivative of vf(lambda,alpha) function. MathCad says it is too long to be shown.

Where? I couldn't find that problem in you worksheet. Obviously I'm missing the point. Always better to post a stripped down worksheets which just shows the error or, as in your case, the undesired behaviour.

As you have defined Alpha at the top I assume you are interested in the derivative wrt lamda. I move the range variable for lamda down a bit.

cohesive2.png

One way to look at an expression which Mathcad 15 says being to long is to convert the worksheet in Prime format and load it in Prime 2, if you have the possibility to do so. Prime would let you scroll - no, unfortunately not, but you are allowed to enlarge the expression region to the right.

H
HarveyHensley12-Amethyst
12-Amethyst
February 10, 2013

Werner,

I was working on this at the same time. I was able to get the derivative when alpha = .5 as was assumed in the worksheet, but the evaluation doesn't complete in a long time when other values for alpha are used. The same happens with your suggestion for the modifiers. When alpa is treated as a variable without a value, then the long result occurs.

Anousheh showed plots with other values of alpha, so I assume there will be an interest in a more general result. Any ideas?

Harvey

W
Werner_E25-Diamond I
25-Diamond I
February 10, 2013

I was already a bit confused why he had already marked the question as being answered, as I guessed that I could not have solved his problem.

I just tried it with generic alpha and yes, I had to stop calculation even at simplifying vf(). The nested functions didn't make following easyier, but I think the main problem seems to be the Gamma-function in N1(alpha) which is used in N(alpha,lamda) whch is used in vf().

Usually with those too long symbolic expression there is not much one can do, on the other hand - what will we do with them? We can use them in following calculations anyway and looking at expressions that long and complex is usually not really helpful.

So when Mathcad is not able to shorten the result its up to us to decide whether we could simplify the instruction, are happy with only part of the solution or can live with the fact that we can use, but no see the derivative. It all depends on what we intend to do with the result.

One last idea is - we could try to make the derivative a function of alpha, if its really the derivation with respect to lamda which is wished for. On the other hand, what would be the benefit, as we can use the too long expression as well?

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