Re: why Pi is not recognized as a positive number?
- To: mathgroup at smc.vnet.net
- Subject: [mg45369] Re: why Pi is not recognized as a positive number?
- From: drbob at bigfoot.com (Bobby R. Treat)
- Date: Sat, 3 Jan 2004 01:35:11 -0500 (EST)
- References: <bt3e0s$plb$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
You left out the question mark:
f[x_?Positive] := x + 1
x_Positive matches expressions with Positive as Head, so for instance:
Clear@f
f[x_Positive]:=x+1
f@Positive[x]
1+Positive[x]
Bobby
Pedro L <pedrito6 at softhome.net> wrote in message news:<bt3e0s$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",
> 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]:="]
> }