cases in definition of a function

cases in definition of a function - How to use for plot or integral - Messages

#1 Posted: 12/2/2016 11:41:14 AM
Martin_B

Martin_B

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Hi,

I have a function using "cases".
Evaluation it for certain values works as I expect it.

But using this function for plotting a graph or as integrand, only a constant value is returned.

I don't know why, but I liked to and particularly I can't find a solution.
File not found.File not found.

I am using SMath 0.98 (6179) on Windows 10 x64
#2 Posted: 12/2/2016 2:34:57 PM
Davide Carpi

Davide Carpi

1416 likes in 2873 posts.

Group: Moderator

Hello [userlink]MarB[/userlink],

This is because when the numerical evaluation of a condition throws an error (if none of the previous conditions was true) or when the result of a true condition return an error, the function returns itself. When cases() returns itself, acts like a function not yet defined; this makes all his content active and evaluable, therefore when it fails n:j and break are both evaluated and you get the first value of j (3).

The solution is to put the assignments out of the cases(...)' arguments

2016-12-02 18_08_24-SMath Studio - [cases_in_function.sm_].png
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#3 Posted: 12/2/2016 2:55:24 PM
Jean Giraud

Jean Giraud

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My interpretation does not mean that your attempt wrt "cases" is not.
Discontinuous functions must be specified completely, same in
Mathcad/Mathsoft taking into account the different "if" coding.

Discontinuous.gif
#4 Posted: 12/2/2016 3:19:51 PM
Jean Giraud

Jean Giraud

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... interesting to see numerical integrator takes "cases".
However of no interest as it will range from very uncertain
to damned erroneous.

Discontinuous [Other].gif
#5 Posted: 12/2/2016 4:09:45 PM
Martin_B

Martin_B

21 likes in 84 posts.

Group: User

Thanks Davide for your help.
I think I am smarter now.
The reason why I tried my supposed solution was, that I "copied" a Mathcad function where I used "return j" instead of "n:j break n" and there it worked fine.
The other reason is, that I thaugt: why test all members of the vector when I know early that I have found the reason.
But this only to be mentioned by the way.

Jean, thanks for your help, too.
The reason for choosing a loop is that the count of the vector my vary and therefore nesting if/else is not practible.
#6 Posted: 12/2/2016 9:01:03 PM
Jean Giraud

Jean Giraud

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Whatever the "if/else" is presented to the user, the nested form
is computable in any number of loops and any size. The attached
example demonstrates a typical loop as it will appear in modern
"Programmable Logic Controller". From visible small sizes to
infinitely large sizes [very large sizes] system for controlling
industrial plants. As you can observe, the "nested" is essentially
based on the user 'recipe'.
The recursive construction belongs to the "logic ToolBox" as well
as the Bolean [not attached].

Integrate Discontinuous [Algo if].sm (52 KiB) downloaded 53 time(s).
#7 Posted: 12/3/2016 12:21:25 AM
Jean Giraud

Jean Giraud

983 likes in 6866 posts.

Group: User

... same document but the recursive section deleted.
There is "shadow in the context".

Integrate Discontinuous [Algo if].sm (34 KiB) downloaded 48 time(s).
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