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-MFra-21-Topaz II
21-Topaz II
December 3, 2016
Question

Limitations of the symbolic derivatives in Prime

  • December 3, 2016
  • 2 replies
  • 3307 views

I would like to point out that in Prime, in calculating symbolic derivatives, the order of derivation can not be written as the sum of two integers but with an index that represents the sum of them, and this, however,  is not written properly, in fact:

Prime symbolic derivative.jpg

2 replies

V
ValeryOchkov24-Ruby IV
24-Ruby IV
December 3, 2016

One more limitation

W
Werner_E25-Diamond I
25-Diamond I
December 3, 2016

All OK in Mathcad 15:

The Prime help does not state that the order of the derivative has to be a constant and not an expression to be evaluated, so I consider it a bug (otherwise it would be a severe, not acceptable limitation).

So, while I consider it as a minor one, its still one more reason not to use Prime yet.

@Valery: Yours is not a limitation of Prime, its a mathematical one - it makes sense to limit the order of the derivative to positive integers, so Prime is OK in this case.

If you are looking for other discrepancies or limitations you may look at the newly introduced Prime operator.

It does not exist in real Mathcad (other than in a limited way in a solve block in conjunction with odesolve -> Ctrl+F7).

This Prime operator would be a nice feature, if it would be better visible and could be applied using a keyboard shortcut on foreign keyboards, too. Unfortunately thats not the case and using the ribbon menu is too tedious. This prime symbol can be cascaded to get higher derivatives, too, which is nice.

Unfortunately PTC forgot to tell the symbolics about this new operator

So again - maybe some day this will be a consistent and useful feature, but not yet. Better keep away from Prime - at least for the next few versions.

V
ValeryOchkov24-Ruby IV
24-Ruby IV
December 3, 2016

Werner Exinger написал(а):

All OK in Mathcad 15:

@Valery: Yours is not a limitation of Prime, its a mathematical one - it makes sense to limit the order of the derivative to positive integers, so Prime is OK in this case.

One limitation of Werner - he do not understand humor

W
Werner_E25-Diamond I
25-Diamond I
December 3, 2016
Valery Ochkov wrote:


One limitation of Werner - he do not understand humor

I indeed have many limitations but in this case that's only partially true: In fact I really very often don't understand YOUR type of humor. But in no way I see this as a limitation 😉

While, as I wrote, it makes sense to limit the order of the derivative to positive integers, its not mandatory to do so! There is a branch in math which deals with "fractional calculus" (e.g. Fractional calculus - Wikipedia). So again one more reason to take your comment as serious and real. If you intended to make a joke it would have been either not fair, given, that there are people out there dealing seriously with this subject, or it simply shows you were not aware of this branch of math analysis - that you really thought that something like a "half-derivative" does not exist and that it would be funny to pretend it does. If the latter applies, you should be a little piece wiser now.

And then - there is so few good we can say about Prime. So if there is an opportunity, we have to grab it (even if its just to say that in one particular case Prime is OK and not wrong). These are still very rare moments.

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