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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg45364] RE: [mg45360] why Pi is not recognized as a positive number?
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sat, 3 Jan 2004 01:35:07 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Peter,

x_Positive is the pattern for an expression that has the Head Positive - not
what your want. You want...

f[x_?Positive] := x + 1

f[Pi]
1 + Pi

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/


From: Pedro L [mailto:pedrito6 at softhome.net]
To: mathgroup 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]:="]
}




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