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FB_106515904-Participant
4-Participant
April 16, 2024
Question

"Solve" command turns for ever

  • April 16, 2024
  • 1 reply
  • 7537 views

In this case I want  to allocate a result of substitution to Eq1, 

It seems to works for the substitution but  then Eq1 seems undefined. What happens?

 

Then it might be the reason why the 2nd substitution is endless.

 

 

However, when i try to make 2 substitution in the same execution command, it is endless too.

What happens  ?  Is there a relation between those 2 cases ?

 

Option calculation for constant unit with symobilc math is set.

PTC MathCAD prime 9.0.0.0.0

    1 reply

    W
    Werner_E25-Diamond I
    25-Diamond I
    April 16, 2024

    You try to evaluate Eq1 numerically (the normal equal sign). Here Prime throws an error because of the derivative of the unknown and probably undefined function Theta.

    Numeric evaluation will only return numeric values, not generic functions or their derivatives.

    Not sure what may cause the "endless" calculation. Its hard to impossible to debug just a picture ...

    F
    FB_106515904-ParticipantAuthor
    4-Participant
    April 17, 2024

    Thank you for your answer.

     

    I now try another approach:

    1-define completely the symbolic formula

    2- then i will define numerical values of known parameters

     

    I expect so to see the formula with some numerical values.

     

    In the following  formula, the result seems unknown, as I would have expect on 2nd line to have the same than 1st line.

    2024-04-17_09h18_28.png

    W
    Werner_E25-Diamond I
    25-Diamond I
    April 17, 2024

    You must realize the difference between numeric evaluation (=) and symbolic evaluation (->)

    Werner_E_0-1713347219149.png

     

    Here some remarks using a simpler example

    Werner_E_1-1713347299096.png

    BTW, even in the last approach a derivative won't work (IMHO it should, but maybe its because Prime would have to do the numeric derivation at definition time which it can't  because the function is unknown at that time?)

    Werner_E_2-1713347429505.png

    nor that way

    Werner_E_3-1713347464074.png

     

     

     

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