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]:="] > } >

**References**:**why Pi is not recognized as a positive number?***From:*Pedro L <pedrito6@softhome.net>