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ptc-47354781-Visitor
1-Visitor
January 20, 2013
Solved

Anyone think the numerical solve block is WEAK?

  • January 20, 2013
  • 12 replies
  • 3657 views

Please check the attached file and change the initial guess value....

I understand a intial guess value is important for a numerical solver....

But for this problem...a deviation of 0.01 from the solution is enough to cause an error while using Find and it only happens in prime 2.0. I think this is telling me to put prime 2.0 in trash!

When solving the exact same system of equation in MC15, the initial guess can practically be any thing....and it always converge with a tolerence of 10^-7

This problem has multiple solution depending on the initial guess. And MC15 can always converge with tiny tolerence and find the corresponding answer. But prime 2.0 cannot!!

BTW, The system of equation is just an exact copy of Harvey Hensley example on a CSTR, which was written in MC15.

http://communities.ptc.com/docs/DOC-2373

Best answer by Werner_E

henry leung schrieb:

Oh..I have F000, an older version..i guess thats why...

Don't know if thats the cause, but sure F000 is the first release from February 2012, M010 is the current release dated October 2012. Vladimir had posted the list of bug fixes for that version http://communities.ptc.com/message/190370#190370

The only bug fix having to do with solve blocks I could spot was

"Fixes an issue where a solve block in Mathcad Prime 2.0 returns incorrect results when constraints are created by copying their definitions"

12 replies

Werner_E
Werner_E25-Diamond I
25-Diamond I
January 20, 2013

I don't know much about Prime so I can only image that you didn't use the same numerical algorithm. In MC15 you would right click the word "find" or "minerr" and usually a good choice is Nonlinear/Levenberg-Marquardt.

I don't know which algorithm Prime defaults to and if and how you can change it there. I remember vaguely reading in the help of Prime that it choses the algorithm automatically. Maybe there is no way to force it to a specific one.

Did you let convert your working Mathcad15 worksheet to Prime format or did you typed it in from scratch?

ValeryOchkov24-Ruby IV
24-Ruby IV
January 20, 2013

Werner Exinger wrote:

I don't know which algorithm Prime defaults

Levenberg-Marquardt

AlanStevens19-Tanzanite
19-Tanzanite
January 20, 2013

Try just clicking on Calculate, within the Calculation Tab. The file worked ok for me when I did this! It seems to be the same idiosyncrasy that Valery has come across a couple of times.

Alan

ptc-47354781-VisitorAuthor
1-Visitor
January 20, 2013

Hi Alan,

I have no luck clicking on Calculate within the calculation tab. Tried F9 and Ctrl+F9 also, still does not work.

When you say the file worked, are you able to converge using Find? what is the tolerance and error you got?

If I deviate from the answer by 0.001, Find fail.

If I deviate from the answer by 0.0001, Find works but still with a greater error than MC 15.......

Anyone know how to choose the numerical method in Prime 2.0??

Werner_E
Werner_E25-Diamond I
25-Diamond I
January 20, 2013

When you say the file worked, are you able to converge using Find? what is the tolerance and error you got?

The results are exactly the same regardless of the offset. See the screenshot for wout:=ans+0.1

numeric1.png

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