if (integer_order < 0)
## You have made a grave mistake.
- df = NA;
+ coefficients = NA;
return;
end
if (integer_order == 0)
- df = x;
+ coefficients = x;
return;
end
if (length(xs) < 2)
## You can't approximate a derivative of order greater than zero
## with zero or one points!
- df = NA
+ coefficients = NA
return;
end