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MathGroup Archive 2007

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Re: Piecewise inside a Module or Block, I don't understand this

  • To: mathgroup at smc.vnet.net
  • Subject: [mg83300] Re: Piecewise inside a Module or Block, I don't understand this
  • From: "W. Craig Carter" <ccarter at mit.edu>
  • Date: Sat, 17 Nov 2007 05:17:25 -0500 (EST)
  • References: <fhjs9v$4vg$1@smc.vnet.net> <473DA496.5050509@gmail.com>

>>  a[c_, d_] :=
>>    Module[{e, f}, e = d^2; f = c^2;
>>     Return[Piecewise[{e, 0 < x < 1/2}, {f, 1/2 < x <= 1}]]];
>>  a[1,2] (*doen't return what I had anticipated*)
>
> All this is just about a syntax error you made.
>
> First, note that, as posted, none of the above examples works: they both

Cher Jean-Marc,
I don't get an error when I cut and paste this expression. 
Math6.01

And, the posted work-around works just fine:
aAlt[c_, d_] :=
Module[{e, f}, e = d^2; f = c^2;
{{e, 0 < x < 1/2}, {f, 1/2 < x <= 1}}];
Piecewise@aAlt[1,2]

Note, that this seems to be peculiar to Piecewise: e.g,

a[c_, d_] :=
     Module[{e, f}, e = d^2; f = c^2;
      Return[MyUnAssignedFunction[{e, 0 < x < 1/2}, {f, 1/2 < x <= 1}]]];
`  a[1,2]

works as I hoped.

PS: My goal here was to write a function that made a calculation of the
bounds, and then returned a piecewise function of x that had the bounds
as explicitly calculated.


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