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Re: idl parallel processing [message #94436 is a reply to message #94433]

Mon, 22 May 2017 12:06

wlandsman
Messages: 743
Registered: June 2000

Senior Member

As I mentioned, you can only use the .hasvalue static method if you have IDL 8.4 or later. If you have an earlier version of IDL you can still get some speed improvement using the following function.

function hasvalue,array, value
; Determine if scalar value is present in array
; Emulates the .hasvalue static method introduced in IDL 8.4
return,~array_equal( array NE value, 1b)
end

and use it like this.

pro computation,data=data,siteN=siteN,result
N = N_elements(siteN)
result=fltarr(N,/nozero)
FOR i= 0,N-1 do result[i] = hasvalue(data, siteN[i])
END

I find hasvalue() is a factor of two faster than using WHERE(), but a factor of five slower than using the .hasvalue method. The actual speed ratios depend on the size of the arrays, and the fraction of time that .hasvalue is true.

On Sunday, May 21, 2017 at 10:59:52 PM UTC-4, Sium T wrote:
> On Friday, May 19, 2017 at 10:59:07 AM UTC-4, wlandsman wrote:
>> Yes, you can use the IDL Bridge for this. But if you have IDL 8.4 or later, then more valuable would be using the .HASVALUE() static method. Your code would then be
>>
>> result= bytarr(n_elements(siteN))
>> FOR i= 0,n_elements(siteN)-1 do result[i] = data.hasvalue(siteN[i])
>>
>> The reasons this is much faster are (1) you don't need to compute the output vector of WHERE(). All you care about is whether the siteN[i] value is present in the data array-- you don't care where it is. And (2) the .hasvalue() method will return as soon as it finds a single case where the siteN[i] value is present, so you skip having to search the entire data array
>>
>> --Wayne
>>
>> On Thursday, May 18, 2017 at 6:05:51 PM UTC-4, Sium T wrote:
>>> Hello,
>>>
>>> I have a procedure below. It want to call my procedure in my main program and do parallel processing on the do loop.
>>>
>>> How can use the IDL_Bridge . Any suggestion
>>>
>>> pro computation,data=data,siteN=siteN,result
>>>
>>> result=fltarr(n_elements(siteN))
>>>
>>> FOR i= 0,n_elements(siteN)-1 do begin
>>> y=where(data eq siteN(i))
>>> if y(0) ge 0 then begin
>>> result(i)=1
>>> endif else begin
>>> result(i)=0
>>> endelse
>>> ENDFOR
>>>
>>> end
>
> Thanks Wayne
>
> I tried your method
> result= bytarr(n_elements(siteN))
> FOR i= 0,n_elements(siteN)-1 do result[i] = data.hasvalue(siteN[i])
>
> However, I got this error message.
>
> Object reference type required in this context:

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[Message index]

		idl parallel processing By: siumtesfai on Thu, 18 May 2017 15:05
		Re: idl parallel processing By: wlandsman on Fri, 19 May 2017 07:59
		Re: idl parallel processing By: siumtesfai on Sun, 21 May 2017 19:59
		Re: idl parallel processing By: Helder Marchetto on Mon, 22 May 2017 02:35
		Re: idl parallel processing By: siumtesfai on Mon, 22 May 2017 12:06
		Re: idl parallel processing By: Markus Schmassmann on Tue, 23 May 2017 05:59
		Re: idl parallel processing By: siumtesfai on Wed, 24 May 2017 15:20
		Re: idl parallel processing By: wlandsman on Mon, 22 May 2017 12:06
		Re: idl parallel processing By: siumtesfai on Mon, 22 May 2017 12:34
		Re: idl parallel processing By: siumtesfai on Mon, 22 May 2017 12:40
		Re: idl parallel processing By: natha on Tue, 23 May 2017 05:29

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