residuals is a generic function which extracts model residuals
from objects returned by modeling functions. The abbreviated form resid is an alias for residuals.
It is intended to encourage users to access object components through
an accessor function rather than by directly referencing an object
slot. All object classes which are returned by model fitting functions
should provide a residuals method. (Note that the method is
for residuals and not resid.) Methods can make use of naresid methods to compensate
for the omission of missing values. The default, nls and
smooth.spline methods do.residuals(object, …)
resid(object, …)object.coefficients, fitted.values,
glm, lm. influence.measures for standardized (rstandard)
and studentized (rstudent) residuals.