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08/27/12 10:22pm

I'm trying to find a simple way in Mathematica to change variables in a differential equation or differential expression (what dchange in PDETools does in Maple). I'm starting with a particularly simple case where I have functions of a single variable r and transform to x=1/r. So let's say I have

exp1[r_] := D[b[r], r] + D[n[r], r]

then I can change variables in one of the functions by doing

exp1[r] /. {b -> Function[r, b[1/r]], r -> 1/x}

but if I try to do a pattern like

exp1[r] /. {f_ -> Function[r, f[1/r]], r -> 1/x}

so that it applies the transformation rule to both b(r) and n(r) (and any other functions I might put in) then I get some unintelligible output. How do I get this change of variables to work?

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Subject (listing for 'Help with changing variables')
Author Date Posted
Help with changing variables Adam 08/27/12 10:22pm
Re: Help with changing variables Bill Simpson 08/28/12 5:04pm
Re: Re: Help with changing variables Adam 08/30/12 12:32pm
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