Re: Fuction definition
- To: mathgroup at smc.vnet.net
- Subject: [mg73686] Re: Fuction definition
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Sat, 24 Feb 2007 02:26:20 -0500 (EST)
- Organization: The Open University, Milton Keynes, UK
- References: <erme23$i63$1@smc.vnet.net>
bar at ANTYSPAM.ap.krakow.pl wrote: > Hi > > When I try : > ------------------ > p = 1; > f1[x_] := p Sin[Pi x]; > p = 2; > f2[x_] := p Sin[Pi x]; > > f1[0.5] > f2[0.5] > > Out[26]=2. > > Out[27]=2. > ----------------- > When I use = instead of := it works OK. > Why ? SetDelayed, :=, evaluates the body of the definition only when the the function is called. Therefore, f1 looks at the value of p only when it is called by f1[0.5]. At that time, the current value of p is 2, not 1. In[1]:= p = 1; f1[x_] := p*Sin[Pi*x]; f1[0.5] Out[3]= 1. In[4]:= p = 2; f2[x_] := p*Sin[Pi*x]; f1[0.5] f2[0.5] Out[6]= 2. Out[7]= 2. > It is safely to use "=" in function definition ? The usual way for defining a function is to use SetDelayed, not Set. > I have to integrate and differentiate such function in the future. > In my case function depends on about 20 parameters, which are calculated > three times, (I want to obtain three functions) You could define your functions in the following way: In[8]:= f3[p_][x_] := p*Sin[Pi*x]; f3[4][0.5] Out[9]= 4. > I'm not sure is this good idea to use '=' ? Short answer: no, not for defining a function. > Regards , Olaf Regards, Jean-Marc