Vectorize my code in azimuth calculation.
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Mani Ahmadian
am 23 Sep. 2014
Kommentiert: Mani Ahmadian
am 25 Sep. 2014
Hi I have lots of points(in Latitude & Longitude) and I want to calculate the azimuth of each pairs of them. I use code as attached file 'AzimuthCalc.m'. when I run my function, it's so time consuming and it's elapsed time is 109.371341 seconds. I'm sure the problem caused by my non-vectorize code.
So, would you please check my function and help me to improve it?
Thanks a lot Mani
2 Kommentare
Adam
am 23 Sep. 2014
Run:
profile on
your code
profile off
profile viewer
and find out where your code is slow. No point in guessing when you can use facts!
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Guillaume
am 23 Sep. 2014
I don't have the mapping toolbox, so I'm just relying on the documentation to write my answer.
For a start, you can replace the inner loop with:
AzimuthPoints(ii,ii+1:end)=azimuth('rh',lat(ii),long(ii),lat(ii+1:end),long(ii+1:end));
I believe the following may work to replace both loops (and the AzimuthPoints declaration)
[lat1, lat2] = meshgrid(lat);
[long1, long2] = meshgrid(long);
AzimuthPoints = azimuth('rh', lat1, long1, lat2, long2);
The downside of this method is that it's going to calculate the whole AzimuthPoints matrix, not just the upper triangle, so it may actually be slower.
You could do:
lat1 = triu(lat1, 1);
%same with lat2, long1 and long2
to replace the lower triangle and main diagonal with zero, on the assumption that calculating
azimuth('rh', 0, 0, 0, 0)
is faster.
5 Kommentare
Guillaume
am 24 Sep. 2014
TrueAzimuth should be 0s and 1s but of type logical. If you used my code to generate it, it shoul already be logical, but if not:
TrueAzimuth = logical(TrueAzimuth);
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Roger Stafford
am 24 Sep. 2014
You could try this. It calls on 'azimuth' in the same sequence as in your for-loop code, but it is vectorized. Whether it is faster depends on whether the 'tril' and 'repmat' calls take less time than the overhead in the for-loops and individual 'azimuth' calls in your code.
n = length(lat);
p = tril(repmat(1:n,n,1),-1);
p = p(p>0);
q = tril(repmat((1:n)',1,n),-1);
q = q(q>0);
AzimuthPoints = zeros(n);
AzimuthPoints(p+n*(q-1)) = azimuth('rh',lat(p),long(p),lat(q),long(q));
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