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MathGroup Archive 2004

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Re: clarification. Re: one liner for a function?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg46070] Re: clarification. Re: one liner for a function?
  • From: sean_incali at yahoo.com (sean kim)
  • Date: Thu, 5 Feb 2004 04:02:50 -0500 (EST)
  • References: <bvg11r$qn6$1@smc.vnet.net> <bvl8r0$t4j$1@smc.vnet.net> <bvnmiu$ha4$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Thank you very much Peltio.  I'm new to this funtional programming
idea. and i have heard that writing pure functions make things go
faster.  so I have been trying to think of things in terms of
funtions.  it's not easy but i think im making a progress.

thanks so much for the codes. 

sean 

"Peltio" <peltio at twilight.zone> wrote in message news:<bvnmiu$ha4$1 at smc.vnet.net>...
> >You might also want to modify
> >the line
> >    newli = li /. (_ -> v_) -> fun[v];
> >to make it look like something like
> >    newli = li /. (a_ -> v_) -> Set[buildname[a],fun[v]];
> 
> It is possible to generalize the procedure ToValues in such a way that you
> can get what you want in this way:
> 
>     sol= NDSolve[{
>         a'[t]==-0.1a[t] x[t], b'[t]==-0.05b[t] y[t],
>         x'[t]==-0.1a[t] x[t]+0.05b[t] y[t], y'[t]==0.1a[t] x[t]-0.05b[t]
> y[t],
>         a[0]==1, b[0]==1, x[0]==1, y[0]==0},
>         {a,b,x,y},{t,0,250}];
> 
> (note that we are assigning the 'raw' list of solutions to ToValues).
> This will plot the graph of the solution, labeling it with the variable's
> name.
> 
>     makePlots[name_][f_] := Plot[f[t], {t, 0, 250},
>         DisplayFunction ->Identity,PlotRange -> All, Frame -> True,
>         FrameLabel -> {"t",ToString[name]}];
> 
> We can map this function on the list of rules given by NDSolve. Using
> ToValues it is possible no to care about the nesting
> 
>     Show[GraphicsArray[
>         Partition[ToValues[sols, makePlots, IndexedFunction -> True], 2]
>     ]]
> 
> 
> And if you still want to assign the plots to variables with names linked to
> the name of the function you can use the following functions:
>     plotName[nm_] := ToExpression[StringJoin["p", ToString[nm]]]
>     setPlots[nm_][f_] := Evaluate[plotName[nm]] = Plot[f[t], {t, 0,250},
>         DisplayFunction -> Identity, PlotRange -> All, Frame -> True];
> We can use ToValues to extract the solutions from the list given by NDSolve
> and apply to them the setPlots function, in order to have plots assinged to
> separate variables. Do not evaluate this command twice unless you have
> cleared the variables used.
>     Show[GraphicsArray[
>         Partition[ToValues[sols, setPlots, IndexedFunction -> True], 2]
>     ]]
> The individual plots are now assigned, as you initially asked, to the
> variables whose names are in the form 'p+name of  the function'. Remember
> that you'd have to force their visualization by setting the proper option in
> Show.
>     Show[py, DisplayFunction -> $DisplayFunction]
> 
> cheers,
> Peltio
> and you need the following generalized version of ToValues to do the above
> (a properly placed subtitution with pure functions will do as well, but... I
> have this hammer now and everything resembles a nail : ) ):
> 
> (* ToValues code follows ==================== *)
> 
> ToValues::usage = "ToValues[li] suppresses the Rule wrapper in every part of
> the list li.\n ToValues[li,F] applies the function F to every rhs of Rule,
> turning var->value into F[value]. If the function F has a parametrized head,
> then it is possible to pass to it the lhs of Rule by setting the option
> IndexedFunction->True. It will turn var->value into F[var][value].\n
> When the option Flattening is set to Automatic, ToValues flattens li in
> order to simplify its structure (the flattening is tuned to get the
> simplest list of values for the solution of a system of several equation
> in several variables). With Flattening set to None the original structure
> is left intact.";
> 
> Options[ToValues] = {Flattening -> Automatic, IndexedFunction -> False};
> 
> ToValues[li_, opts___Rule] := Module[
>     {newli, vars, sols, fl},
>     fl = Flattening /. {opts} /. Options[ToValues];
>     sols = First[Dimensions[li]]; vars = Last[Dimensions[li]];
>     newli = li /. (_ -> v_) -> v;
>     If[fl == Automatic && vars == 1, newli = Flatten[newli]];
>     If[fl == Automatic && sols == 1, First[newli], newli]
> ]
> 
> ToValues[li_, fun_, opts___Rule] := Module[
>     {newli, vars, sols, foo, mi},
>     mi = IndexedFunction /. {opts} /. Options[ToValues];
>     fl = Flattening /. {opts} /. Options[ToValues];
>     If[mi == True,
>         newli = li /. (x_ -> v_) -> foo[x][v],
>         newli = li /. (_ -> v_) -> foo[v]
>     ];
>     sols = First[Dimensions[li]]; vars = Last[Dimensions[li]];
>     If[fl == Automatic && vars == 1, newli = Flatten[newli]];
>     If[fl == Automatic && sols == 1, First[newli], newli] //. foo -> fun
> ]
> 
> (* end of code ============================ *)
> An example of application:
> 
> cmplxToVec[z_]:={Line[{#,{0,0}}],PointSize[.018],Point[#]}&/@{{Re[z],Im[z]}}
> 
>     vecs=ToValues[Solve[x^9==1,x], cmplxToVec ];
>     Show[Graphics[vecs], AspectRatio->1,Frame->True,Axes->True];


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