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Re: Need a function to multiply the elements of an array [message #4142 is a reply to message #4065]

Fri, 28 April 1995 00:00

VUKOVIC
Messages: 6
Registered: December 1994

Junior Member

In <3nohst$sun@pinot.umd.edu% barsam@Glue.umd.edu writes:

% In article <3nm2uk$qqq@pinot.umd.edu%,
% I wrote:
% %
% %Hi,
% %
% %I am looking for a routine to multiply the elements of an array.
% %Is there a faster way of doing it than the following?
% %
% %
% %function prod, x
% %n = n_elements(x)-1
% %z = 1.d0
% %for i = 0, n do z = z * x(i)
% %return, z
% %end
% %
% %
% %
% %BM
% %
%
% Thanks for the replies.
%
% z = exp(total(alog(x))) gives me about 60% savings. Not terribly
% fast but obviously better than the "for" loop.
%
% BM
%
%
That is strange (or I am strange), but I would think naively
expect that in the "for" loop you have only N multiplications, while
taking log of each number gives you M*N multiplications, where M is the
number of multiplications used to evaluate the log of a number.

I guess if going for speed, it would be fairly simple to write a fortran/c
routine to do it

Mirko

Mirko Vukovic | vukovic@uwmfe.neep.wisc.edu
Dept. of Nucl. Eng. and Eng. Phys. | mvukovic@wiscmacc.bitnet
U of Wisconsin -- Madison | phone: (608) 265-4069
1500 Johnson Drive; Madison WI 53706| fax: (608) 265-2364

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[Message index]

		Need a function to multiply the elements of an array By: barsam on Wed, 26 April 1995 00:00
		Re: Need a function to multiply the elements of an array By: VUKOVIC on Mon, 01 May 1995 00:00
		Re: Need a function to multiply the elements of an array By: isaacman on Fri, 28 April 1995 00:00
		Re: Need a function to multiply the elements of an array By: chase on Fri, 28 April 1995 00:00
		Re: Need a function to multiply the elements of an array By: VUKOVIC on Fri, 28 April 1995 00:00
		Re: Need a function to multiply the elements of an array By: rlw on Fri, 28 April 1995 00:00

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