fitlm works but polyfit does not work

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alpedhuez 2020-12-6

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https://ww2.mathworks.cn/matlabcentral/answers/682658-fitlm-works-but-polyfit-does-not-work

评论： Ameer Hamza 2020-12-6

I run polyfit and fitlm for the same data. fitlm provides an output. But polyfit and corrcoef return NaN. How can it be?

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Catalytic 2020-12-6

Who knows? You've provided no means for us to reproduce what you see.

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Answer 1

Ameer Hamza 2020-12-6

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https://ww2.mathworks.cn/matlabcentral/answers/682658-fitlm-works-but-polyfit-does-not-work#answer_566818

编辑：Ameer Hamza 2020-12-6

在 MATLAB Online 中打开

There is probably NaN somewhere in your dataset. fitlm() ignores those data values. For example

x = linspace(0, 1, 10);
y = 2*x + 3 + rand(size(x));
y(3) = nan;
p = polyfit(x, y, 1)
c = corrcoef(y)
ft = fitlm(x, y)

Result

>> p
p =
   NaN   NaN
>> c
c =
   NaN
>> ft
ft = 
Linear regression model:
    y ~ 1 + x1
Estimated Coefficients:
                   Estimate      SE       tStat       pValue  
                   ________    _______    ______    __________
    (Intercept)     3.1773     0.13254    23.973    5.5901e-08
    x1              2.3847     0.21348     11.17    1.0268e-05
Number of observations: 9, Error degrees of freedom: 7
Root Mean Squared Error: 0.206
R-squared: 0.947,  Adjusted R-Squared: 0.939
F-statistic vs. constant model: 125, p-value = 1.03e-05