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Werner_E25-Diamond I
25-Diamond I
July 3, 2018
Solved

Symbolic bug

  • July 3, 2018
  • 3 replies
  • 5449 views

YASB

Yet Another Symbolics Bug

 

I don't expect PTC to fix this bug in the near or far future but just out of curiosity - does anybody has an explanation or idea whats going wrong internally in the symbolics here (other than "its a bug").

B.png

 

I did not take the time to convert to Prime but I expect the same error there, too.

MC15 worksheet attached.

    Best answer by LucMeekes

    Notice how 133-3sqrt(1965) is close to 0.

    Taking that to the fourth power (in the third term of the 'expand' result) gets it even closer to 0.

    I renamed 133 to a and sqrt(1965) to r.

    a-3r=0.015, (1-3r)^4=5e-8

    The second term of the numerator of the 'expand-simplfy' result would be:

    LM_20180704_SymbolicBug1.png

    And that's a real zero. A non-zero number raised to whatever (real) power should never become 0, or am I going crazy?

     

    Luc

     

     

    3 replies

    L
    LucMeekes23-Emerald IV
    23-Emerald IV
    July 4, 2018

    Here's Mathcad 11 / Maple. Of course without error Smiley Tongue Might help to clarify...

    LM_20180704_SymbolicBug.png

    In the attached file, I've put the simplified, expanded and the expanded-simplified expressions as new variables. Maybe working with those in M15 brings you further in clarifying.

     

    Success!
    Luc

      W
      Werner_E25-Diamond IAuthor
      25-Diamond I
      July 4, 2018

      Thanks for the reply, Luc!

      I had no doubt that Maple in MC11 would do it correct.

      The simplifications done using the various keywords are completely different as our screenshots show - not surprising.

      Its well known that Maple is far superior compared to MuPad, but that error in a simple numeric only expression is quite alarming!

      L
      LucMeekes23-Emerald IV
      23-Emerald IV
      July 4, 2018

      Taking a closer look, I'd guess (just guess...) that 'simplify' causes the error. Look at how all answers (except the obviously wrong one) are 2.43342766, except for the numeric result of simplification only: 2.43342768.

      A difference of 2 at position 7, that's too large to simply result from numeric inaccuracy (17 positions!) alone.

       

      Luc

       

      V
      24-Ruby III
      VladimirN24-Ruby III
      24-Ruby III
      August 22, 2018

      What service release of Mathcad 15?

      F
      Fred_Kohlhepp23-Emerald I
      23-Emerald I
      August 22, 2018
      @VladimirN wrote:

      What service release of Mathcad 15?

      There is anecdotal evidence that Prime is using a very old version of MuPad.  It's highly improbable that they would have upgraded 15 on service release when the current software is so dated.

      V
      24-Ruby III
      VladimirN24-Ruby III
      24-Ruby III
      August 22, 2018

      Here is a result in Mathcad 15 M045:

      Pic-1.png

       

      And in Mathcad Prime 3.1:

       

      Pic-2.png

      F
      Fred_Kohlhepp23-Emerald I
      23-Emerald I
      August 22, 2018

      Q E D

       

      Same MuPad version

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