Re: Fine control of evaluation

*To*: mathgroup at smc.vnet.net*Subject*: [mg126460] Re: Fine control of evaluation*From*: Brentt <brenttnewman at gmail.com>*Date*: Sat, 12 May 2012 04:53:50 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <13064693.4533.1336710718460.JavaMail.root@m06>

Thank you. I didn't know about the presentations package. Neat. On Fri, May 11, 2012 at 9:09 AM, djmpark <djmpark at comcast.net> wrote: > This is easy using either the EvaluateAt or EvaluateAtPattern functions in > the Presentations Application. > > << Presentations` > > func1[x_] := f[x]; > func2[x_] := g[x]; > > HoldForm[func1[x] + func2[x]] > % // EvaluateAt[{1, 1}] > > func1[x] + func2[x] > f[x] + func2[x] > > HoldForm[func1[x] + func2[x]] > % // EvaluateAtPattern[_func1] > > func1[x] + func2[x] > f[x] + func2[x] > > > David Park > djmpark at comcast.net > http://home.comcast.net/~djmpark/index.html > > > From: Brentt [mailto:brenttnewman at gmail.com] > > > Hello, I am struggling with evaluation control and was hoping someone might > point me in the right direction. I vaguely remember seeing something in the > manual or the tutorials addressing this issue, but I can't find the section > I saw it in. > > How does one get fine control over things wrapped in Hold and HoldForm. Say > I have some functions > > func1[x_]:= f[x]; > func2[x_] := g[x]; > step1 = HoldForm[ func1[x]+ func2[x] ]; > > Now say I want the statements wrapped in HoldForm, func1[x]+ func2[x] to > evaluate to f[x]+ func2[x] > > I thought naturally it would be something like > > step2 = HoldForm[ Evaluate[func1[x]]+ func2[x] ] ; > > But then HoldForm seems a bit overzealous about it's task, and outputs > Evaluate[func1[x]]+ func2[x]---it leaves Evaluate unevaluated. (I tried > wrapping it func1[x] in ReleaseHold to no avail.) > > The above is just pseudocode, Maybe there is some specifics about what I > was > actually doing that was causing the unintuitive behavior (i.e. HoldForm > holding Evaluate, instead of, well, evaluating.) What I was doing was more > along these lines: > ---------------- > ubounds= {u,0, pi}; > vbounds={v,0,2pi}; > t[dir_]:= D[s[u,v],dir_]; (*where dir_ is going to be either u or v*) > > (*here is the difficult part:*) > formattedOutput= Integrate[HoldForm[t[u]] , ubounds, vbounds ] > //TraditionalForm; > ---------------- > The issue is that I want the t[u] wrapped in the HoldForm to evaluate to > D[s[u,v],dir_], and hold that. If I wrap it in Evaluate, HoldForm holds > Evaluate (puzzling), and tries to integrate Evaluate as if it is the > integrand. I've tried all kinds of permutations of HoldForm, Defer, > ReleaseHold, Evaluate, and I haven't had anything to work. > > Thank you for any help or pointing me in the right direction > >