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Re: why Pi is not recognized as a positive number?

• To: mathgroup at smc.vnet.net
• Subject: [mg45363] Re: why Pi is not recognized as a positive number?
• From: "Bo Le" <bole79 at email.si>
• Date: Sat, 3 Jan 2004 01:35:07 -0500 (EST)
• References: <bt3e0s$plb$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Hi,


Your first definition has a mistake. A typo?

One types g[x_Positive] to define g to arguments with head Positive
(g[x_Real] would be more sensible), while f[x_?Positive]  to define f to
arguments which have this property. More generally, h[x_?test] defines h to
arguments, on which the application of test returns True.

Your second definition of f is of course correct and also more common, as it
is read as 'only when x is Positive'.


Bye,

Borut
Slovenia



"Pedro L" <pedrito6 at softhome.net> wrote in message
news:bt3e0s$plb$1 at smc.vnet.net...
>   I wanted to define a function for the positive numbers. But I discovered
>   something "strange" with Mathematica.
>
>   Could you help me with this?
>
>   Thanks in advance.
>
>   Peter L  (Spain)
>
>
>
> {
>
> Cell[CellGroupData[{
> Cell[BoxData["$Version"], "Input",
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>
> Cell[BoxData["\<\"5.0 for Microsoft Windows (June 11, 2003)\"\>"], \
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> }, Open  ]],
>
> Cell[BoxData[
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>       RowBox[{"f", "[", "x_Positive", "]"}], ":=",
>       RowBox[{"x", "+", "1", "  "}]}]], "Input",
>   CellLabel->"In[2]:="],
>
> Cell[CellGroupData[{
>
> Cell[BoxData[
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>   CellLabel->"In[3]:="],
>
> Cell[BoxData["True"], "Output",
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> }, Open  ]],
>
> Cell[CellGroupData[{
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> Cell[BoxData[
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>   CellLabel->"In[4]:="],
>
> Cell[BoxData[
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> }, Open  ]],
>
> Cell[BoxData[
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>
> Cell[BoxData[
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>   CellLabel->"In[6]:="],
>
> Cell[CellGroupData[{
>
> Cell[BoxData[
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>
> Cell[BoxData[
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>   CellLabel->"Out[7]="]
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>
>