Pattern match exception problem

[ifomenko]

Hi

I`m trying to make simple calculation but without success. What`s the problem?

MC15 file is attached for convenience.

Thanks in advance.

[LucMeekes]

I get this in Mathcad 11.

(The error messages are the same for all red evaluations).

Apparently it's not 'simple'.

Success!
Luc

[ifomenko]

Problem is in delta function, if you change it by 1 for example everything is OK.

If you change double sum by two summing loops inside program block everything is OK too!See attached file

[LucMeekes]

Then don't use the delta function, but use (i=j) instead:

Success!
Luc

[LucMeekes · Accepted solution]

Or use this alternative definition of it:

(The symbolic processor is not so fond of programming constructs, it likes pure mathematical expressions better.)

Success!
Luc

[ifomenko]

Problem is not to find answer but understand why mistake is.

But thank you for very short and elegant delta function and it really works!!!

[Werner_E]

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@ifomenko wrote:

Problem is not to find answer but understand why mistake is.

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The reason for the error is, that Mathcads symbolics always try to evaluate and simplify symbolically all used expressions and functions before it applies specific values or patrameters.

Obviously it can't symbolically evaluate an if-statement, because it usually can't know if the condition is fulfilled or not, as this depends on the values of the specific arguments.

In case of your double sum Mathcad could know which branch to chose, but it looks like it tries to evaluate and simplify the expression in the sum before the sum is evaluated.

[ifomenko]

Thank you, I forgot that symbolic engine doesn`t like branching.

[ifomenko]

One very simple and interesting result

[Werner_E]

Thats exactly the very same problem as you had here

https://community.ptc.com/t5/PTC-Mathcad/Symbolic-issue/td-p/655681/jump-to/first-unread-message

Seems like the symbolic doesn't like strings

I just gave it a try in Prime 6 and the new symbolic (while in many cases weaker and less capable even compared to muPAD) does not have this problem: