Re: Defining N for a new entity
- To: mathgroup at smc.vnet.net
- Subject: [mg66762] Re: Defining N for a new entity
- From: Giuseppe Bilotta <bilotta78 at hotpop.com>
- Date: Mon, 29 May 2006 06:06:10 -0400 (EDT)
- References: <200605280103.VAA23345@smc.vnet.net> <e5bsuq$afo$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
On Sun, 28 May 2006 10:10:34 +0000 (UTC), Carl K. Woll wrote:
> Giuseppe Bilotta wrote:
>> So I was looking for a way to tell Mathematica that applying N to an
>> AffineExpression should only actually apply it to c and xi, something
>> like
>>
>> N[AffineExpression[c_, dev_]] :=
>> AffineExpression[N[c], MapAt[N,#,{2}]&/@ dev]
>>
>> but if I actually do this and then call
>>
>> AffineExpression[1, {{1, 1}}]
>> N[%]
>>
>> the Mathematica kernel (5.2.0.0) dies without any message.
>>
>> Does anybody have an idea of what could the reason be? And what could
>> I do as a workaround?
>
> One idea is to use the attribute NHoldRest (or if you change your data
> structure, NHoldFirst). For example:
>
> SetAttributes[AffineExpression, NHoldRest]
>
> In[42]:= N[AffineExpression[.5, {{1, .2}, {2, .1}}]]
>
> Out[42]= AffineExpression[0.5, {{1, 0.2}, {2, 0.1}}]
Thank you very much, this does the trick. It has the rather small
side-effect of preventi N from working on the coefficients
(N at AffineExpression[.5,{{1,Pi/6}}] will not numerize Pi/6), but it's
good enough for my application.
Do you have any ideas on why the Mathematica kernel dies without a
message?
--
Giuseppe "Oblomov" Bilotta
"E la storia dell'umanità, babbo?"
"Ma niente: prima si fanno delle cazzate,
poi si studia che cazzate si sono fatte"
(Altan)
("And what about the history of the human race, dad?"
"Oh, nothing special: first they make some foolish things,
then you study what foolish things have been made")
- References:
- Defining N for a new entity
- From: Giuseppe Bilotta <bilotta78@hotpop.com>
- Defining N for a new entity