Place polyfit values in a matrix using a loop

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Nathan Kennedy 2018-2-8

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评论： Star Strider 2018-2-13

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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

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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 2018-2-8

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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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Nathan Kennedy 2018-2-13

My mistake, thank you for this!

Star Strider 2018-2-13

As always, my pleasure!

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