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Re: slot argument weirdness

  • To: mathgroup at smc.vnet.net
  • Subject: [mg83934] Re: slot argument weirdness
  • From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
  • Date: Wed, 5 Dec 2007 07:04:51 -0500 (EST)
  • Organization: The Open University, Milton Keynes, UK
  • References: <fj37b2$hok$1@smc.vnet.net>

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:

This is normal since you have defined is an incomplete pure function. In 
other words, Slot must always be accompanied by & to form a syntacticly 
correct expression.

> 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.

v = {2, 5};
m = {{#1, #2}, {#2, #1}} &;
Apply[m, v]
m @@ v

Regards,
-- 
Jean-Marc



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