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R
rcarr-21-Visitor
1-Visitor
June 25, 2013
Solved

MathCAD 14 symbolic solver

  • June 25, 2013
  • 2 replies
  • 4836 views

I recently installed MathCAD14, upgrading from MathCAD7. I just noticed today that unlike the symbolic solver of MathCAD7, the symbolic solver in MathCAD14 appears unable to solve the magnitude of a complex number symbolically. Did anyone else come across this? Is this a bug, or am I doing something wrong?

mc14.jpg

MC7.jpg

Any comment s appreciated,

Ray

Best answer by Werner_E

As Valery already pointed out the symbilc engine in MC14 and above is muPad, the engine in older versions was Maple, considered by many users as the better one.

muPads behaviour is sometiome annyoing, while mathematically perhaps more correct than that of Maple. Maple obviously is implicitely assuming that X and Y are real values as most of us would do, too, as the "formula" for calculating the absolute value you have in mind is valid for real X and Y only:

symb_abs2.png

So if you want to assume X and Y as real values, you have to tell muPad explicitely so. Additionally you have to demand muPad you want it to simplify the expression.

symb_abs.png

Maple assumed by default variables and results to be real values and you could change that by using the modifier "complex".

muPad (unfortunately!?) defaults to "complex" and making it think "real" can be quite a challenge sometimes.

2 replies

V
24-Ruby IV
ValeryOchkov24-Ruby IV
24-Ruby IV
June 26, 2013

It is an old problem.

Matcad 7 has the symbolic engine from Maple and Mathcad 13(?)-15 and Prime - from MuPAD.

Send pleade your sheet and we will try to help you.

W
Werner_E25-Diamond IAnswer
25-Diamond I
June 26, 2013

As Valery already pointed out the symbilc engine in MC14 and above is muPad, the engine in older versions was Maple, considered by many users as the better one.

muPads behaviour is sometiome annyoing, while mathematically perhaps more correct than that of Maple. Maple obviously is implicitely assuming that X and Y are real values as most of us would do, too, as the "formula" for calculating the absolute value you have in mind is valid for real X and Y only:

symb_abs2.png

So if you want to assume X and Y as real values, you have to tell muPad explicitely so. Additionally you have to demand muPad you want it to simplify the expression.

symb_abs.png

Maple assumed by default variables and results to be real values and you could change that by using the modifier "complex".

muPad (unfortunately!?) defaults to "complex" and making it think "real" can be quite a challenge sometimes.

R
rcarr-21-VisitorAuthor
1-Visitor
June 26, 2013

Thank you all for your quick responses. I feel much better about MC14 now. I also tried the modifier ALL=real which works fine too.

allreal.jpg

However, with something a bit more complex, I wonder if something else is needed:

MC7:

MC7B1.jpgMC7b2.jpg

MC14:

MC14b.jpg

W
Werner_E25-Diamond I
25-Diamond I
June 26, 2013

As already indicated it can be tricky to convince MC to simplify expressions the way we expect it to do. Sometimes muPad is simply unable to do (its not the best symbolic processor one can imagine), sometimes we are making implicit assumptions we often are not aware of.

Most of the time we end up in trial and error, playing around with the keywords and modifiers. And ever so often MC would ignore a given conditions - thats especially true with the "assume" command.

I didn't typed in the expression but what you can try is "assume, ALL>0", "simplify,max" and somtimes "factor" helps even if we are not interested in a factorization. There are situations where even the order the keywords are typed is important.

After all its an unsatisfyable situation that the possibilities to influence the way symbolic evalauations are done are so much limited.

As Valery already wrote - to make it easier for us you its better to attach a worksheet. You can do so by clicking in the upper right "Use advanced editor".

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