Speed of wave assignments using wave reference waves

If you write something like MyWave[] = waveRefWave[0] * x I assume the wave declaration is done over and over again for each point of MyWave

How many enries does the wave reference wave has? I suppose two is just for playing around? If yes, have you seen https://www.wavemetrics.com/code-snippet/using-wave-reference-waves-mul…? This would allow you to get rid of the do/while loops and thus should be much faster.

How much is a decent bit faster?

My tests with Igor 8.04 on Windows, using a machine with an 8 core/16 thread processor, show no consistent difference between the two:

•testfunc()
  Assigned:  0.500324  s
  Not assigned:  0.477222  s
•testfunc()
  Assigned:  0.453647  s
  Not assigned:  0.516939  s
•testfunc()
  Assigned:  0.481404  s
  Not assigned:  0.483658  s

Interesting. I just did 20 repeat tests of it and the 'assigned' version was faster every time.

Assign: 1.29 s avg

Not assigned: 1.47 s avg

I'm on 8.05 Mac, 4 core i7

@olelytken, that might make sense, but my (mistaken?) impression was that the wave is already declared as waveRefWave[0], so no red-declaration has to happen. 

@Thomas, yes just two entries for the purposes of testing this out. It's about 170 ms faster for me on this code, so about 11%. It seems to be constant though-- if I take out the multithreading, 'Not assign' is about the same amount slower than 'Assign', even though the overall runtime is much slower. And I hadn't seen that before, but that's very useful thank you!

OK, I see the problem, my original unassigned loop wasn't doing what I thought and may just be copying the wave reference itself into all the rows/cols/layers of the output wave. Looks like I do need to explicitly declare each wave reference in the wave ref wave before using it. 

Ben Murphy-Baum wrote:

OK, I see the problem, my original unassigned loop wasn't doing what I thought and may just be copying the wave reference itself into all the rows/cols/layers of the output wave. Looks like I do need to explicitly declare each wave reference in the wave ref wave before using it. 

This seems like a bug to me. I'll report this to the author of that code.

@aclight Could you post here once that is resolved? I'd like to have a look if and how that influences my code.

thomas_braun wrote:

@aclight Could you post here once that is resolved? I'd like to have a look if and how that influences my code.

Larry has changed Igor 9 so that this gives a compile error on the dd += ww[i] line:

Function test()
    Make/O wave0 = 1, wave1= 2
    Make/O ddd = 0
    Make/O/N=2/WAVE ww
    ww[0]=wave0
    ww[1]=wave1
    
    Variable i = 0
    Do
        ddd += ww[i]
        i++
    
    While (i<2)
 
End

Instead, you would need to write the loop like this:

    Do
        WAVE theWave = ww[i]
        ddd += theWave
        i++
    
    While (i<2)