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Place polyfit values in a matrix using a loop

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Nathan Kennedy
Nathan Kennedy 2018-2-8
评论： Star Strider 2018-2-13
Hi
I want to capture all the values from the polyfit function in a matrix when it is in a loop.
for a=1:length(x)
temp_x=x(1:a)
temp_y=y(1:a)
p(a,:) = polyfit(x,y,3); % Not working as intended
end
The polyfit function generates 4 values in a 1 row 4 column array. So I would like to end up with a matrix that has rows equal to the length of x and 4 columns containing the polyfit values for each iteration of the loop.
Please can someone advise
  1 个评论
John D'Errico
John D'Errico 2018-2-8
Are you thinking this will create something like a cubic spline? Or some sort of local cubic interpolation? If so, there are better methods. Far better choices you can make.

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Star Strider
Star Strider 2018-2-8
I am not certain what you want to do, specifically because you are not doing anything with ‘temp_x’ and ‘temp_y’.
Perhaps you intend something like this:
for a=1:length(x)-3
temp_x = x(1:a+3)
temp_y = y(1:a+3)
p(a,:) = polyfit(temp_x,temp_y,3);
end
Note that to do a third-order regression, you must have at least four elements in the data vectors.
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