Re: slot argument weirdness
- To: mathgroup at smc.vnet.net
- Subject: [mg83968] Re: slot argument weirdness
- From: dh <dh at metrohm.ch>
- Date: Wed, 5 Dec 2007 07:22:52 -0500 (EST)
- References: <fj37b2$hok$1@smc.vnet.net>
Hi Jerry,
you are nearly there. If you set:
m = {{#1, #2}, {#2, #1}}&;
all is well.
The reason for this is, that ...& is a function. Functiosn has the
attribute HoldAll what prevents from the replacement of m by its value.
You get a function that always returns m. This leaves m that is
subsequently evaluated. Another solution that forces the evaluation, is:
Apply[Evaluate[m] &, v]
hope this helps, Daniel
Jerry wrote:
> I have to produce some bulky matrices which are described by
> two parameters and it seems the easiest way to produce them
> is as follows (I took out all the complexity and just left
> in the slots to illustrate my problem). v is the parameter
> array.
>
> v = {2, 5};
> myMatrix=Apply[{{#1, #2}, {#2, #1}} &, v]
>
> giving {{2, 5}, {5, 2}} and all is well.
>
> But since the actual form in the first argument in Apply is
> really a large messy thing, I thought I'd produce it just
> once in the notebook and represent it with:
>
> m = {{#1, #2}, {#2, #1}};
>
> But geez, this doesn't work at all:
>
> MyMatrix2= Apply[m &, v]
>
> gives {{#1, #2}, {#2, #1}}
>
> I've tried a lot of things to make this work but have failed
> completely. If someone can tell me that there is absolutely
> no representation of the slot configuration that will do
> what I want, then I can quit trying. Or is there? Thanks for
> any info.
>