linear fit with fitlm or regress

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Andreas Grøvan Aspaas 2019-5-13

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评论： Andreas Grøvan Aspaas 2019-5-15

I have a data set of three variables. I want to use the equation y = a + b*temp + c*temp* sigma. When i write this like y~temp+(sigma*temp) in fitlm, I get 4 terms, Intercept, temp, sigma and temp:sigma.

My question is if sigma is the slope c and temp:sigma is temp*sigma for the c? I think this is correct, but I have not been able to figure out how the equation would look like based on the input arguments. The displayed "Linear regression model" is y ~1 + t*sigma

Thanks a lot!

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Jeff Miller 2019-5-14

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在 MATLAB Online 中打开

Your three variables are y, temp, and sigma? If I understand the model you want to fit, you might get a cleaner picture if you form a new variable:

prod = temp.*sigma;

and then use

y~temp+prod

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Jeff Miller 2019-5-14

Sorry, I just don't understand what model you are trying to fit. You say you are trying to get

y = (a0+b0*T) + (c0*sigma+d0*T)

but that does not look like a legitimate model to me as I said before.

Andreas Grøvan Aspaas 2019-5-15

Ok. It might not work. I was just thinking that I should be able to make whatever formula I wanted if I told matlab to make it.

I think the prod method you proposed works though. I do not get c0 and d0, but I get them both combined if I am not wrong. And this is enough as I just need to know how significant it is. It would be better to have them separated, but as I am not able to I am going to just accept it.

Thanks a lot for taking the time!

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