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]:="] > }