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KevinGilman1-Visitor
1-Visitor
March 3, 2011
Question

Symbolic processing not working well in MCAD 15 verses earlier versions

  • March 3, 2011
  • 3 replies
  • 2670 views

Here's a simple example, solve for P....

Capture.PNG

In MCAD 7 the result is

Capture2.JPG

Which is easily manipulated to

Capture3.JPG

In MCAD 15 the result is

Capture4.PNGThe result goes on for days......

What is the problem? Is the symbolic processor "improved" in MCAD 15?

3 replies

L
LucMeekes23-Emerald IV
23-Emerald IV
March 3, 2011

Kevin,

Going from Mathcad version 13 to 14 the symbolic processor Maple has been changed to MuPad. For some types of expression that is an improvement, for others it isn't.

Luc

P
Philip.Oakley1-Visitor
1-Visitor
March 3, 2011

There is no problem <wink>

It is just that with the MuPad German efficiency it wants to cover all bases including negative and complex parameters.

Many of the old Maple answers are "wrong" in that they assume common conventions without telling you.

If you have a look at some of the tutorial / quicksheet examples they show how there are some updated keywords you proaobly want to use to state that the variable are real and positive (gt zero).

The knack is to look at the result and see which conditionals MuPad has thrown into the symbolic answer to see which you need to explicitly avoid.

You will see the result has various pi values in it. That is because e^(i.pi) = -1, so when you take the general logarithm for your power term you get all sorts of nasties.

Philip

R
RichardJ19-Tanzanite
19-Tanzanite
March 3, 2011

Kevin Gilman wrote:

Here's a simple example, solve for P....

Capture.PNG

In MCAD 7 the result is

Capture2.JPG

Yes, but it is actually, in general, not correct.

Which is easily manipulated to

Capture3.JPG

Easily, but in general incorrectly.

Why are the above not correct? Because, as Philip points out, the symbolic processor does not necessarily make the assumptions you do about the domains of the variables. This is especially true of the new MuPad engine in versions 14 and 15. The MuPad engine is giving you the correct answer, just a confusing one. See the attached worksheet for more details, and for how to get what you want.

Another good example of this (which I have given frequently in these forums) is to simplify the square root of the square of X. Most people seem to think this should simplify to X, but that is not correct. Then add the assumption that X is real. Then change that assumption so that X is real and positive.

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