| Re: Undocumented array indexing feature? [message #14166 is a reply to message #14114] |
Tue, 26 January 1999 00:00   |
Martin Schultz
Messages: 515
Registered: August 1997
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Senior Member |
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R.Bauer wrote:
>> Bill B. wrote:
> [...]
>> Oh, I knew that one, Alex. Anyone know which method offers faster execution -
>>
>> a = 0 & b = 0 * OR * a = (b = 0)
>>
>> this is important when applying the same principle to large arrays. At least
>> to those of us with slower PCs :(
>
> Initializing of big arrays should be done by a=make_array(200,100000,/nozero)
> This is the fastest method
>
> R.Bauer
but then you have them uninitialized! A fair comparison is
a = make_array(dim1,dim2,type)
Here is some timing info (IDL 5.1 on SGI Origin 2000):
[only one pass each, but these numbers don't change much]
A1 = FLTARR(1000,1000) & A2 = FLTARR(1000,1000)
0.031656981 + 0.032227993 = 0.063884974 seconds
B2 = ( B1 = FLTARR(1000,1000) )
0.085137010 seconds
C1 = MAKE_ARRAY(1000,1000,/FLOAT) & C2 = ...
0.037186027 + 0.040596962 = 0.077782989 seconds
D1 = MAKE_ARRAY(1000,1000,/FLOAT,/NOZERO) & C2 = ...
0.00017607212 + 0.00011897087 = 0.00029504299 seconds
Regards,
Martin.
--
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Dr. Martin Schultz
Department for Engineering&Applied Sciences, Harvard University
109 Pierce Hall, 29 Oxford St., Cambridge, MA-02138, USA
phone: (617)-496-8318
fax : (617)-495-4551
e-mail: mgs@io.harvard.edu
Internet-homepage: http://www-as.harvard.edu/people/staff/mgs/
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