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Re: Re: Hold and Equal
*To*: mathgroup at smc.vnet.net
*Subject*: [mg73771] Re: [mg73747] Re: Hold and Equal
*From*: Murray Eisenberg <murray at math.umass.edu>
*Date*: Wed, 28 Feb 2007 04:29:07 -0500 (EST)
*Organization*: Mathematics & Statistics, Univ. of Mass./Amherst
*References*: <erufqm$s7j$1@smc.vnet.net> <200702271048.FAA24024@smc.vnet.net>
*Reply-to*: murray at math.umass.edu
Aha! I believe this approach _almost_ allows me to accomplish what I
was REALLY trying to accomplish. It certainly works in the example I
gave. If I encapsulate this in a function...
formEquation[expr_, op_]:= HoldForm[expr=z]/.z\[Rule]op[expr]
... then
formEquation[(a+b)^2,Identity]
will produce exactly what I want.
However, if I try something like the example I was really after (which I
didn't mention in my original post, since I gave something simpler), it
works in the direct version...
HoldForm[Integrate[x^2,x] = z] /. z\[Rule]Integrate[x^2,x]
but not with the encapsulating function:
formEquation[Integrate[x^2, x], Identity]
The latter produces the equation
x^3/3 = x^3/2
whereas I want the left-hand side to be the unevaluated integral expression.
You can tell I'm struggling with Hold! (One of the "last frontiers" in
my Mathematica education.)
bghiggins at ucdavis.edu wrote:
> Murray,
>
> Try this
>
>
> HoldForm[(a + b)^2 = z] /. z -> Expand[(a + b)^2]
>
>
> (a + b)^2 = a^2 + 2*a*b + b^2
>
> Cheers,
>
> Brian
>
>
>
> On Feb 26, 3:20 am, Murray Eisenberg <mur... at math.umass.edu> wrote:
>> How can I produce in an Output cell (under program control) an
>> expression like the following,
>>
>> (a+b)^2 = a^2+ 2 a b + b^2
>>
>> where instead of the usual Equal (==) I get a Set (=), as in traditional
>> math notation? I want to input the unexpanded (a+b)^2 and have the
>> expansion done automatically.
>>
>> Of course, I can try something like the following:
>>
>> (a+b)^2 == Expand[(a+b)^2])
>>
>> So how do I convert the == to =? Of course
>>
>> ((a + b)^2 == Expand[(a + b)^2]) /. Equal -> Set
>>
>> gives a Set::write error. And
>>
>> (Hold[(a + b)^2 == Expand[(a + b)^2]]) /. Equal -> Set
>>
>> doesn't actually evaluate the Expand part and leaves the "Hold" wrapper.
>>
>> --
>> Murray Eisenberg mur... at math.umass.edu
>> Mathematics & Statistics Dept.
>> Lederle Graduate Research Tower phone 413 549-1020 (H)
>> University of Massachusetts 413 545-2859 (W)
>> 710 North Pleasant Street fax 413 545-1801
>> Amherst, MA 01003-9305
>
>
>
--
Murray Eisenberg murray at math.umass.edu
Mathematics & Statistics Dept.
Lederle Graduate Research Tower phone 413 549-1020 (H)
University of Massachusetts 413 545-2859 (W)
710 North Pleasant Street fax 413 545-1801
Amherst, MA 01003-9305
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