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Re: How to map a list on function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg97715] Re: How to map a list on function
  • From: Vince <blueschi at gmail.com>
  • Date: Thu, 19 Mar 2009 02:13:04 -0500 (EST)
  • References: <gpg18t$ceh$1@smc.vnet.net>

On Mar 14, 6:35 am, buts <mange... at yahoo.com> wrote:
> Hello,
>
> Could anyone explain me how to do the following:
> I have a long list of integer numbers in groups of four:
>
> list= {{10,3,5,7},{4,6,8,9},{0,8,3,6}, ...... }
>
> or its Flatten version.
>
> How to write a fast function g[list] which does this:
>
> g[list] =x^10*y^3*z^5*u^7 + x^4*y^6*z^8*u^9 + y^8*z^3*u^6+ ...
>
> It should be done many times (say, 10^4-6) on lists with length > 1000, so taking parts is not a good idea.
> How to use Map or similar ?
> Thanks.

Use Listability. Try:

Plus @@ Times @@  Power[{x, y, z, u}, Transpose@{{10, 3, 5, 7}, {4, 6,
8, 9}, {0, 8, 3, 6}}]

Some timing for other list lengths---1 000 000 gives ~ 18 seconds, 10
000 gives ~ 0.1 seconds, and 1000 gives ~ 0 seconds.

Vince Virgilio



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