The goodness of fit of a regression line is the percentage
of the variance of the y values that is explained by the
dependence on the x values.
Set the alpha value of the regression line to this goodness
of fit.
Further, set the width of the regression line to a standard
deviation of the values from the regression line valies.
Signed-off-by: Robert C. Helling <helling@atdotde.de>
d83c9b5246