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Re: Looking for more ideas on code ... [message #32353 is a reply to message #32269]

Tue, 01 October 2002 19:44

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

JD Smith <jdsmith@as.arizona.edu> writes:
> That certainly the canonical "tricky" way to get an array of 1's, and, at
> least on my machine, it's actually faster for most array sizes than:
>
> profile=make_array(n_elements(y),/FLOAT,VALUE=1.)
>
> I started to write this to demonstrate how certain tricks like this can be
> inefficient, only to find it's actually *more* efficient in most cases.
>
> Hmmph. Live and learn.

Interesting performance result! I do it because it allows me to
control the type and dimension of the output array pretty simply. The
effects of the following statement can be pretty subtle:

y = x*0 + 1.

This statement guarantees that Y has the same dimensions as X (except
for trailing unit dimensions darnit). But the other nice thing this
does is guarantee a certain minimum data type for Y.

Because I am adding the floating point value "1.", Y is guaranteed to
be at least floating point. *BUT* if X is double precision, then Y
will be double precision as well. This is a nice way to keep the
internal precision consistent without resorting to the awkward and
error-prone "DOUBLE" keywords that pepper the IDL library.

Craig

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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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[Message index]

		Re: Looking for more ideas on code ... By: JD Smith on Tue, 01 October 2002 08:12
		Re: Looking for more ideas on code ... By: Craig Markwardt on Mon, 30 September 2002 17:55
		Re: Looking for more ideas on code ... By: jeyadev on Tue, 01 October 2002 13:11
		Re: Looking for more ideas on code ... By: Craig Markwardt on Tue, 01 October 2002 19:44

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