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lvl10720-Turquoise
20-Turquoise
January 8, 2017
Solved

solve, symbolic ==> real number solution ?

  Hello, Everyone.

From :

(1).PNG

    Is there a symbolic :,f(x),solve, symbolic ==> real number ?

         Thanks in advance.

               Regards.

Werner_E
Werner_EAnswer
25-Diamond I
January 8, 2017

Mathcads symbolics simply is not reliable and capable enough. So either stay with the numerics or switch to another tool.

Sometime you can achieve different results using substitutions, but whenever Mupad switches to numeric approx mode itself, it seems to be impossible to control the outcome (by using assume,...).

Who would have thought that a dummy substitution which should not affect the equation or the way MuPad solves it influences the outcome that much?

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4 replies

Werner_E
Werner_E25-Diamond IAnswer
25-Diamond I
January 8, 2017

Mathcads symbolics simply is not reliable and capable enough. So either stay with the numerics or switch to another tool.

Sometime you can achieve different results using substitutions, but whenever Mupad switches to numeric approx mode itself, it seems to be impossible to control the outcome (by using assume,...).

Who would have thought that a dummy substitution which should not affect the equation or the way MuPad solves it influences the outcome that much?

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lvl10720-TurquoiseAuthor
20-Turquoise
January 8, 2017

I greatly appreciate your time and help, Werner.  

Yours :

(b).PNG

but my MC15 show :

(a).PNG

Could you please attach ***.xmcd ? ( might be my typing is incorrect )

      Thanks again.

            Best Regards.

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Werner_E
Werner_E25-Diamond I
25-Diamond I
January 8, 2017

Thats funny! When I open your new file, I get the very same result.

Unfortunately I forgot to attach my file and had not kept it, so I can't send it.

The reason for the error ist that now Mathcad delivers something completely different when we use the substitution

At least the strange behavior when we simply use the keyword "substitute" could be reproduced (even though we get a different value as result now).

When I played around the first time I also experienced some other strange effects - the numeric results of the symbolic solver changed when I recalculated the sheet.

I have no explanation for all this and no advice other than not to rely on Mathcad for things like those.

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