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M
MW_102283815-Regular Member
5-Regular Member
April 27, 2026
Solved

WHY? Its stealing my nerves

  • April 27, 2026
  • 2 replies
  • 129 views

Please help me what am i doing wrong?
Mathcad Prime 11.0.1.0

Best answer by Werner_E

“root” is not a modifier for symbolic evaluation like you tried:

Solving using the symbolic engine has to use “solve” but as the symbolics can’t deal with units I did not succeed in talking the symbolics into returning the real result of the cubic equation only.

Here is how to get the result using the “root” function in its two flavors

For completeness sake here how to do it using a solve block with “find”

 

2 replies

W
Werner_E25-Diamond I
25-Diamond I
April 28, 2026
  1. WHY are you stealing our nerves by posting the same question six times? 😉
    At the top you can read

    which means that the forum is temporarily under moderation. Postings get published only after being reviewed by a moderator. So it may take a while for your post to appear on the forum. I suspect that how long it takes may also depend on the time of day. 
    EDIT: In the meantime a friendly moderator has deleted the superfluous duplicate threads - so everything's fine.

  2. WHY are you posting just a picture which does not show how your variables are defined and what the error message exactly is (guess its “no solution found”)? Always attach your worksheet if ever possible. unfortunately the PTC Mathcad Forum does not allow to attach Mathcad files directly so you are forced to archive them (ZIP, RAR, ...) and attach the archive.

  3.  WHY are you using the assignment/definition operator (:=) when you intend to provide an equation for the symbolics to solve? Use the Boolean “Equal To” comparison operator instead and see if this solves your problem:


    The errors following this region stem from the fact that by using the assignment operator you try to (re)define sigma.bzul but because the region fails this variable now is undefined.

  4. BTW, as you are just looking for a numeric value (d.mind) you may consider using the “root” function instead of the symbolic “solve”. Using a solve bock with “find” may also be an (ugly looking) option.

 

M
MW_102283815-Regular MemberAuthor
5-Regular Member
April 28, 2026

Thanks for the clarification.

I did not realise that posts are currently moderated before being published. In other forums I am used to seeing posts appear immediately, so I assumed something went wrong with my connection or browser and tried again. That was my mistake.

I also did not think about ZIPping the Mathcad file. I agree that it is awkward that Mathcad files cannot be attached directly in the Mathcad forum, but now I know how to handle it.

The actual mistake was using the definition operator := instead of the Boolean equal operator = for the symbolic solve. I know about the Boolean equal operator, but I forgot about it there — or rather ignored it because I was tired and annoyed. That explains the issue.

I have mostly used solve so far, but it often returns complex solutions and I usually had to restrict it with assume, real. I have not used root before, but for this kind of numeric diameter calculation it probably makes more sense.

Please ignore the messy structure of the worksheet. It is just a working file I use while studying for exams, not a clean final document.

I was tired and frustrated yesterday, so the post came across more annoyed than intended. Thanks for the help.
 

W
Werner_E25-Diamond IAnswer
25-Diamond I
April 28, 2026

“root” is not a modifier for symbolic evaluation like you tried:

Solving using the symbolic engine has to use “solve” but as the symbolics can’t deal with units I did not succeed in talking the symbolics into returning the real result of the cubic equation only.

Here is how to get the result using the “root” function in its two flavors

For completeness sake here how to do it using a solve block with “find”

 

    M
    MW_102283815-Regular MemberAuthor
    5-Regular Member
    April 28, 2026

    Vielen Dank, jetzt ist es klarer.

    Ich hatte root falsch interpretiert und eher wie einen symbolischen Operator benutzt. Jetzt ist mir klar, dass root() numerisch arbeitet und entsprechend anders eingesetzt werden muss.

    Ich habe bisher meistens solve verwendet, weil ich damit lange Formeln bequem nach der gesuchten Variable umstellen kann. Bei solchen technischen Berechnungen ist das zum Herleiten der Formel für mich recht praktisch. Das Problem ist dann aber, dass solve bei Potenzen natürlich alle mathematischen Lösungen liefert und dadurch auch komplexe Ergebnisse erscheinen.

    Für die eigentliche numerische Berechnung des positiven realen Durchmessers ist root() mit Startwert bzw. Suchbereich oder ein Lösungsblock mit find() daher sinnvoller. Die umgestellte Formel kann ich dann separat sauber für die Dokumentation verwenden.

    Danke auch für das Beispiel-Worksheet.

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