Degrees or Radians for angle data?

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Tim Bennett
Tim Bennett 2013-4-3
I'm calculaing regression coefficients from three sets of angle data ([1 x 20] each) as predictor variables using the following code:
X = [ones(length(x1),1) x1' x2' x3'];
B = X\devY';
However, the coefficients obtained are completely different depending on whether I input the angle data as degrees or radians. Therefore,
1) Why does the change in units result in a large difference in the coefficients based on the same data? 2) The different coefficients mean I need to justify the units I will be using to calculate the coeffcients. Any help here would be appreciated.
Any help would be appreciated.
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Image Analyst
Image Analyst 2013-4-3
Do you also change the units of devY when you change the units of X?
Tim Bennett
Tim Bennett 2013-4-4
Hi Walter,
the units of devY remain the same. The X predictor variables are joint angles and the Y output variables are related to the position of the foot in meters. I've will attach the code and data i'm using below.

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回答（1 个）

the cyclist
the cyclist 2013-4-3
Are you able to supply a small dataset that shows the problem you are talking about? As you describe it, a uniform factor (unit change) should certainly not affect the coefficients of your model.
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the cyclist
the cyclist 2013-4-4
编辑：the cyclist 2013-4-4
Your coefficients simply differ from each other by a factor of 180/pi, the conversion from radians to degrees. This is exactly as expected.
These coefficients presumably have units, just as the inputs do.
Matt Tearle
Matt Tearle 2013-4-4
What the cyclist said. If you're solving Xb = y for b and X is in degrees and y is in meters, then b is in meters/degree. Switch X to radians and b will have to change to meters/radian as well.

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