Skip to main content
W
WalterSchrabmai12-Amethyst
12-Amethyst
December 23, 2020
Solved

symbolic substitutions - who could help

  • December 23, 2020
  • 2 replies
  • 12852 views

Hi 

I have a big formula where I would like to make 3 symb substitutions. But I get an error.

I would need this formula to minerr it to this 3 new Values and not to the k-values.

I would be happy if someone could find a solution. THANKS

I use PRIME 6.0

 

Best answer by WalterSchrabmai

Thank you very much, for your sophisicated advice. But I do not really know, how I could break this formula in much more simplier form. Anyway I did also the manuall subsitution of the analytic solution at all.

It is really bad from ptc that they will discontinue the muPAD, as it is much better, as you said.

 

Merry X-MAs!

2 replies

W
WalterSchrabmai12-AmethystAuthor
12-Amethyst
December 23, 2020

Here is my complete Work, Thanks for any ideas and advices.

L
LucMeekes23-Emerald IV
23-Emerald IV
December 23, 2020

That sure is a big formula. Did you type it in by hand? I don't see it being derived, because it's the very first occurrence of u3 in your file.

If it were the result of symbolic operations, Prime would probably have complained about the size of the result.

 

Anyway. Considering that there are "exp()" in there, instead of "e^" I think you are using the new symbolic processor, instead of MuPad. Did you already try using the alternative symbolic processor (=MuPad)?

 

Success!

Luc

 

W
Werner_E25-Diamond I
25-Diamond I
December 24, 2020

The problem is not the "substitute" command. The symbolic engine can't handle that expression even if you just try to evaluate it symbolically without further symbolic modifications. It runs into that "unknown error"  and it doesn't make any difference which of the two symbolic engines available in Prime 6 you chose.

The reason may be due to Primes infamous autolabeling or its simply because the expression is far too large for the interface to hand it over to the symbolic engine. To find out if its the latter you may try to shorten the expression step by step by deleting parts of it up to the point where the symbolic evaluation starts to work.

I tried a numeric evaluation just to rule out that it is a mistake due to incorrect or incomplete bracketing (you have a lot of unnecessary parentheses). Numeric eval works OK. so this seems not to be the problem.

Werner_E_0-1608770492781.png

You may try to split the function into a couple of smaller auxiliary functions. Here is a simplified example

 

Werner_E_0-1608771254990.png

 

W
WalterSchrabmai12-AmethystAuthor
12-Amethyst
December 24, 2020

Dear Werner_E thanks a lot. I did so, as you also can see it in my complete works.

But unfortunately I do get different result-vectors by the same SSE/deg_of_Freedom.

My Idea is that the fitting with the k-values is more stable and more robust than the fitting by the V1,V2,t21 and clearance. 

I am thankful for any useful advices.

Edit: I also tried to substitute the analy. solution of the ODE with the pragmatical relationships. But without success.

Edit: I found the bug: I missed the factor a in N2

image.png

W
WalterSchrabmai12-AmethystAuthor
12-Amethyst
December 24, 2020

Even I could minerr and optimize the analytical solution of the ODE the substitute-problem still exists:

Here I separated the substitute problem in the other way - and also no success.

 

image.png

Terms & ConditionsAccessibility statement