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Re: Need a function to multiply the elements of an array [message #4141 is a reply to message #4065]

Fri, 28 April 1995 00:00

chase
Messages: 62
Registered: May 1993

Member

>>>> > "Rick" == Rick White <rlw@sundog.stsci.edu> writes:
In article <3nr9e0$2dp@sundog.stsci.edu> rlw@sundog.stsci.edu (Rick White) writes:

Rick> In article <3nm2uk$qqq@pinot.umd.edu>, barsam@Glue.umd.edu (Barsam Marasli) writes:

Rick> |> I am looking for a routine to multiply the elements of an array.

Rick> Here is one more approach for this problem. I did some tests and found
Rick> it to be roughly the same speed as the previous approaches (using logarithms)
Rick> for short vectors (< 100 elements), but it is faster by about a factor
Rick> of 3 for long vectors. It is about 15 times faster than a direct loop
Rick> for long vectors.

It would be nice if IDL had the equivalent of the Scan operator in the
APL language. This is equivalent to partial sums for a vector using
an arbitrary binary operator (+, x, min, max, etc.).

A related recursive operation that I have wanted on occasion is an
auto-regressive (AR) filter. IDL can easily implement moving-average
filters (via convol) but it does not have an efficient function for
impelmenting AR (or ARMA) filters. The most useful generalization of
this would be implementations of multi-input, multi-output linear
time-invariant (or time-varying) state space equations like those in
the matlab signal processing and image processing packages.

Native functions for these types of operations would be an order of
magnitude faster over IDL loop implementations.

Just wishing,
Chris
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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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