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Re: why Pi is not recognized as a positive number?
*To*: mathgroup at smc.vnet.net
*Subject*: [mg45361] Re: [mg45360] why Pi is not recognized as a positive number?
*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>
*Date*: Sat, 3 Jan 2004 01:35:05 -0500 (EST)
*References*: <200401020923.EAA26179@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
The definition
f[x_Positive] := x + 1
means that is x is an expression with head Positive that f[x] should
return x+1. So:
f[Positive[dog]]
1+Positive[dog]
The Head of Pi is not Positive, it is
Head[Pi]
Symbol
Presumably what you really intended was:
Clear[f]
f[x_?Positive]:=x+1
f[Pi]
1+Pi
Andrzej Kozlowski
Chiba, Japan
http://www.mimuw.edu.pl/~akoz/
On 2 Jan 2004, at 18:23, Pedro L wrote:
> {
>
> Cell[CellGroupData[{
> Cell[BoxData["$Version"], "Input",
> CellLabel->"In[1]:="],
>
> Cell[BoxData["\<\"5.0 for Microsoft Windows (June 11, 2003)\"\>"], \
> "Output",
> CellLabel->"Out[1]="]
> }, Open ]],
>
> Cell[BoxData[
> RowBox[{
> RowBox[{"f", "[", "x_Positive", "]"}], ":=",
> RowBox[{"x", "+", "1", " "}]}]], "Input",
> CellLabel->"In[2]:="],
>
> Cell[CellGroupData[{
>
> Cell[BoxData[
> RowBox[{"Positive", "[", "Pi", "]"}]], "Input",
> CellLabel->"In[3]:="],
>
> Cell[BoxData["True"], "Output",
> CellLabel->"Out[3]="]
> }, Open ]],
>
> Cell[CellGroupData[{
>
> Cell[BoxData[
> RowBox[{"f", "[", "Pi", "]"}]], "Input",
> CellLabel->"In[4]:="],
>
> Cell[BoxData[
> RowBox[{"f", "[", "\[Pi]", "]"}]], "Output",
> CellLabel->"Out[4]="]
> }, Open ]],
>
> Cell[BoxData[
> RowBox[{"Remove", "[", "f", "]"}]], "Input",
> CellLabel->"In[5]:="],
>
> Cell[BoxData[
> RowBox[{
> RowBox[{"f", "[",
> RowBox[{"x_", " ", "/;", " ",
> RowBox[{"x", ">", "0"}]}], "]"}], ":=",
> RowBox[{"x", "+", "1"}]}]], "Input",
> CellLabel->"In[6]:="],
>
> Cell[CellGroupData[{
>
> Cell[BoxData[
> RowBox[{"f", "[", "Pi", "]"}]], "Input",
> CellLabel->"In[7]:="],
>
> Cell[BoxData[
> RowBox[{"1", "+", "\[Pi]"}]], "Output",
>
> CellLabel->"Out[7]="]
> }, Open ]],
>
> Cell[BoxData[
> RowBox[{"Remove", "[", "f", "]"}]], "Input",
> CellLabel->"In[8]:="]
> }
>
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