Re: How to evaluate parts of an expression, but not other parts?

*To*: mathgroup at smc.vnet.net*Subject*: [mg122693] Re: How to evaluate parts of an expression, but not other parts?*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Sun, 6 Nov 2011 05:56:06 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <201111050945.EAA10308@smc.vnet.net>

On 5 Nov 2011, at 10:45, Julian Francis wrote: > Dear all, > > I'd like to use the TreePlot function to visualise the expression of a > dynamic programming problem I am working on. > > If I have something like: ( (a+b) + (c+d ) > > Mathematica helpfully simplifies this to: a + b + c + d > > But I'd prefer it to be in the original form. > > I can't write Hold[ ( (a+b) + (c+d) )] because I do want a,b,c & d to > be evaluated. > > I want to write something like: > Hold[ ( (Evaluate[a]+Evaluate[b]) + (Evaluate[c]+Evaluate[d]) ) ] > > But this just leaves the Evaluate expressions unevaluated. > > Any help greatly appreciated. > > Thanks, > Julian. > Well, there may be a simpler way, but here is one that comes to my mind: a = x; b = y; c = z; d = w; HoldForm @@ Apply[Hold, Hold[(a + b) + (c + d)], {2}] /. p_Hold :> With[{w = Plus @@ p}, w /; True] HoldForm[(x + y) + (w + z)] Andrzej Kozlowski=

**References**:**How to evaluate parts of an expression, but not other parts?***From:*Julian Francis <julian.w.francis@gmail.com>