Re: Mathematica- Use a previous equation into the function Function

*To*: mathgroup at smc.vnet.net*Subject*: [mg111457] Re: Mathematica- Use a previous equation into the function Function*From*: Albert Retey <awnl at gmx-topmail.de>*Date*: Mon, 2 Aug 2010 07:04:15 -0400 (EDT)*References*: <i33cvi$87q$1@smc.vnet.net>

Am 01.08.2010 10:58, schrieb Camille: > Dear All, > > I am fairly new to mathematica. I am stuck with a problem I cannot solve. I would like to call a previous equation into the function Function. If a type directly the expression or copy paste it, it works. However, when I call the expression by its name it does not. > Here is the code for a more precise explanation: > > In: ll > Out: d + a x + h x^2 + b y + e x y + c z + j z^2 > > In: Function[##, a x + b y + c z + d + e x y + h x^2 + j z^2] & @@ {Listp} > Out: Function[{a, b, c, d, e, h, j}, > a x + b y + c z + d + e x y + h x^2 + j z^2] > > It works well and I can use it to generate as many equations I want by replacing the variables a,b,c,d,e,h,j. > But if I do: > > In:Function[##, ll] & @@ {Listp} > Out:Function[{a, b, c, d, e, h, j}, ll] > > And I cannot use it. > > Any suggestions? Function @@ {##, ll} & @@ {Listp} or Function[##, Evaluate[ll]] & @@ {Listp} should do what you want. The deeper reason is the HoldAll-Attribute that Function has set: In[9]:= Attributes[Function] Out[9]= {HoldAll, Protected} The two examples above make sure the body of the function is evaluated. Some other possibilities will not work, since Function is also a scoping construct and some renaming might not turn out as intended: In[6]:= With[{l = ll}, Function[##, l]] & @@ {Listp} Out[6]= Function[{a$, b$, c$, d$, e$, h$, j$}, d + a x + h x^2 + b y + e x y + c z + j z^2] hth, albert