MATLAB: Polyfit returns NaN values in p

nanpolyfit

I want to do a linear regression on the response Y (attached)with a predictor vector X. Therefore, I used Matlab polyfit function: [p,s,mu]=polyfit(X,Y,1) but it returns p=[NaN,Inf]
I have Inf values in vector Y. Is it the cause?

Best Answer

Yes. infs in your data will surely cause NaNs, and essentially garbage results. Drop them out first if you expect something meaningful.
y = [rand(10,1);inf];
x = rand(11,1);
p = polyfit(x,y,1)
p =
   NaN   Inf
Surely you don't expect anything reasonable to come out of such a computation with INFs in it. What would the slope of such a line be with some data points at infinity? Of course, any such point at infinity would have infinite leverage.
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