How to use polyfit instead of fit for fitting an exponential. For GPU processing.

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Kris Hoffman
Kris Hoffman 2019-3-13
评论： Walter Roberson 2019-3-13
Ok, I've been fighting this for way too long, and I've posed a similar question to this months ago, but I still do not get the values I so desparately need.
How do I use polyfit to get the 'b' value in the output from fit(X,Y,'exp1')?
I've taken the natural log of every combination of value, used polyval in various ways, and still get nothing within 5 orders of magnitude to what I need. I've read many different answers to this same question in the community, so if you post a link to one, I've probably seen it.
This would be moot if I could use fit with a GPU.
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Matt J
Matt J 2019-3-13
You can use gpuArray operations inside the objective function. In doing so, you can potentially gain speed advantages from your GPU.
It is probably a good idea for you to describe the structure of TE and SSS so we can better delve into how you would optimize the computation time. Are you looping over i,j and computing a separate pair [x1,x2] for each one? What are the dimensions of TE and SSS?
Walter Roberson
Walter Roberson 2019-3-13
If i and j are both scalars, then you only need one squeeze() there instead of 2. You could also use
SS = reshape(SSS(i,j,:), [], 1);

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Matt J
Matt J 2019-3-13
编辑：Matt J 2019-3-13
For example,
a=1;
b=2;
x=gpuArray.linspace(0,2,100);
y=a*exp(b*x);
p=polyfit(x,log(y),1);
b_fit=p(1),
produces the desired value,
b_fit =
2
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Kris Hoffman
Kris Hoffman 2019-3-13
that startpoint is not absolutely necessary. I've tried it without as well and I get within 2% of the same fit.
I am much more concerned about this workaround to DRASTICALLY reduce processing time. Right now it takes 1.5hrs to process each data set on a quad core 3.1 GHz i7. If I run this through a supercomputer utilizing 48 xeon cores it takes 15 minutes. Now, theoretically, if I could pump this data through thousands of CUDA cores, it should be much faster than 15 minutes.
I NEED the b value from the exponential fit output OR if fit could be made to work with CUDA.
I have yet to find any solution that produces even the same sign (+/-) between the two methods.
Walter Roberson
Walter Roberson 2019-3-13
polyfit runs on GPU.
If you are requiring 1.5 hours to do the fit() or polyfit then I would worry you would exceed the memory capacity of your GPU.

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