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May 22, 2014
02:22 AM

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May 22, 2014
02:22 AM

PDE Problem

Hi,

I have entered a sample problem 8.14 from"Mathcad for Chemical Engineers" Adidharma and Temyanko.The PDE is shown in red.I have tried to research the problem but have not had any luck. Is the the PDE outside of of the solver block and this is what is causing an error. Please advise.

Solved! Go to Solution.

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May 23, 2014
07:00 AM

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May 23, 2014
07:00 AM

I can't tell what you made wrong because you didn't send your worksheet.

Andy may be right in assuming that you didn't delete the multiplications you created when you used the vector index. It may also be that you forgot about a vector index.

When you typed f[z(r,z) Mathcad created automatically f[z*(r,z) because MC does not support vectors of functions that way. You will see that implizit multiplication dot only when you are editing the expression.

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May 22, 2014
05:34 AM

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May 22, 2014
05:34 AM

The problem is that you consequently had used the vector/matrix index when you should have used the literal index. The literal index is used in that kind of solve blocks to denote a partial derivative.

You typed f[z(r,z) but should have typed f.z(r,z).

May 23, 2014
03:39 AM

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May 23, 2014
03:39 AM

Hi Werner,

I studied your solution and implemented your correction however I still receive have the PDE statement in red and error message I receive is "This variable is undefined". Please advise if I not formating or inserting the "Given"statment correctly or am I missing something else. Thank you in advance.

Sincerely,

Walter Stonas

May 23, 2014
03:57 AM

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May 23, 2014
03:57 AM

Hello Walter,

There are a number of instances where what looks OK on screen isn't quite the form that Mathcad needs.

(See the group Mathcad madhouse).

In this case you have

but the form Mathcaqd needs is

The difficulty is that this cannot be easily seen if the equation is not the selected one (in focus).

The first is f.z * ( ... )

the second is the function that you require. f.z( ... )

Hope this helps

Andy

May 23, 2014
07:00 AM

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May 23, 2014
07:00 AM

I can't tell what you made wrong because you didn't send your worksheet.

Andy may be right in assuming that you didn't delete the multiplications you created when you used the vector index. It may also be that you forgot about a vector index.

When you typed f[z(r,z) Mathcad created automatically f[z*(r,z) because MC does not support vectors of functions that way. You will see that implizit multiplication dot only when you are editing the expression.

May 23, 2014
09:19 PM

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May 23, 2014
09:19 PM

Werner, Thank you very much for your help. I revisited the calculation sheet after reading your advise and found the error. Thank you A Westerman for you tip; this helped me find the second error.