Speed comparison between polyfit and A\y

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Karthik
Karthik 2012-6-20
I have a program where I am fitting a straight line to a set of data repeatedly over a million times. I wanted to get the most efficient possible code for doing this and thought polyfit would be the way to go. Surprisingly I found that polyfit is about 60 times slower than a simple A\y type estimation. I used the code below to test this out. Why is polyfit so slow ?
X = 0:50;
Y = X + 0.3 + randn(size(X));
N = 1000;
tic
for count = 1:N
temp = polyfit(X,Y,1);
end
tm = toc;
disp(sprintf('Polyfit too %g ms per call',tm/N/1e3));
tic
for count = 1:N
temp = [ones(length(X),1) ,reshape(X,length(X),1)] \ reshape(Y,length(Y),1);
end
tm = toc;
disp(sprintf('A\\y too %g ms per call',tm/N/1e3));
The output is
Polyfit took 614.351 micro seconds per call
A\y took 10.2792 micro seconds per call
Karthik

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采纳的回答

per isakson
per isakson 2012-6-20
Study the performance of the code with the function, profile. Thus
profile on
code under test
profile viewer
Note especially that this line is dark red
0.97 1000 72 elseif warnIfLargeConditionNumber(R)

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