Re: [Newbie] Interpreting output

*To*: mathgroup at smc.vnet.net*Subject*: [mg56658] Re: [Newbie] Interpreting output*From*: Peter Pein <petsie at arcor.de>*Date*: Mon, 2 May 2005 01:32:40 -0400 (EDT)*References*: <d51nl8$cu9$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

MC wrote: > Hi everybody.... > > I'm having troubles in interpreting the output of Mathematica. > > My problem is to define a function F(x,y,z) such that: > F = (whatever) if x>c > F=(whatever) if x<=c > > I achievied this using /; > > When I derive F with respect to one of the variables, the result is a mess. > Just an example with 1 variable: > > f=x/;x>0; > f=-x^2/;x<0; > This is not a function. > D[f,x]=-2Condition(1,0)[x^2,x<0]+Condition(1,0)[x^2,x<0]Less(1,0)[x,0] > > Even in this very simple case, the result is a real mess: > I really do not know how should I read that...and I'm wondering if > I have defined the function in the right way. > > Anybody so kind to explain me what's goung on? > > Thank you very much for your patience > If you want a function: In[1]:= f[x_]:=Piecewise[{{x,x>0},{-x^2,x<0}},0]; f'[x]//InputForm Out[2]//InputForm= Piecewise[{{-2*x, x < 0}, {1, x > 0}}, Indeterminate] looks nice without InputForm. Piecewise is new in version 5.1. For older versions: In[3]:= f4[x_]:=Which[x<0,-x^2,x>0,x]; f4'[x] Out[4]= Which[x<0,-2 x,x>0,1] -- Peter Pein Berlin