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JBlackhole16-Pearl
16-Pearl
November 4, 2018
Solved

Find / Solve definition issue

To all

 

Dug out an old mcad sheet and was hoping to had a "check" but I am having a problem in properly defining either a Find or use the solve option. It's very embarrassing 

 

Can someone advise the mistake I made in setting either option? see attached mcad 15 sheet

 

Thanks

Regards

 

 

Werner_E
Werner_EAnswer
25-Diamond I
November 4, 2018
@JBlackhole wrote:

Thanks. I don't use the solve that often. I tried because I saw some rather good stuff done by users like yourself , LucMeekes to mention only two of them


Of course I like symbolic solutions very much as they are exact and more general and useful in more ways than a single numeric solution.

But the symbolics reaches its limits quite quickly when it gets more and more complex and for technical applications a numeric solution often is all thats needed.

Luc BTW is still using Mathcad 11 and so he is still enjoying Maple as symbolics engine rather than MuPad. So he often is able to find symbolic solutions where users of Mathcad 15 or Prime have to lay down their arms.

 

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5 replies

Werner_E
Werner_E25-Diamond I
25-Diamond I
November 4, 2018

Looks like you have a typo in your sheet. You defined "ft2" but used "fty" for solve and the solve block.

The symbolics will not find a solution even if you change "fty" to "ft2" but the solve block gives you happily the solution 249.995. You also may use the "root" command in one of its two flavors to solve for the variable.

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    JBlackhole16-PearlAuthor
    16-Pearl
    November 4, 2018

    Thanks. This is very embarrassing! A copy-paste and not paying attention!

    Out of interest: Why does the symbolic solve does not work in this case?

     if one does 1 - (expression in bracket)=0 then Solve find a solution. It's an imaginary with the real part =-249.976

    (Even if I force assume ,s=real)

     

    Thanks

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    Werner_E
    Werner_E25-Diamond I
    25-Diamond I
    November 4, 2018

    Mathcad's symbolics is rather weak since they replaced Maple by muPad with version 14.

    The symbolics solver is known to ignore assume-statements when its "forced" (by an equation it can't solve analytically) to switch into numerics mode.

    Its also no unusual that a simple manual help like putting all on one side of the equations as you had done helps the symbolics enough to turn an unsolvable equation into a solvable one.

    Its nice that Mathcad includes symbolics but symbolic calculations are not the main business of the program, its just a nice-to-have.

     

    BTW, I was not able to duplicate what you wrote. The solvee still will run "forever"

    B.png

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