Some confusion on polyfit?

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Jesse 2014-8-21

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https://ww2.mathworks.cn/matlabcentral/answers/151735-some-confusion-on-polyfit

评论： Star Strider 2014-8-21

采纳的回答： Star Strider

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Greetings all,

This one is throwing me for a loop. So I have some data that I was preforming a linear fit on with the basic fit tool GUI, and I receive the coefficients
Coefficients:
p1 = -0.0068338
p2 = 3.9156

Cool - so I wanted to double verify if these numbers were good, so I used the polyfit command:

[fitResults1,S1,mu1] = polyfit(xdata1,ydata1,1)

but I get different coefficients:

-0.1138 2.4694

So, I generated code from the plot to show me what command they are using to get the first sent of coefficients, and they are using polyfit like me, except it's of the form:

fitResults1 = polyfit(xdata1, ydata1, 1)

Notice it's not in brackets as described in http://www.mathworks.com/help/matlab/ref/polyfit.html

but why are the coefficients so different between the two? I double checked everything (i.e., if xdata1 was the x data from my plot and ydata1 was the y data from my plot, and it was).

Did I stumble on a bug?

Thanks!