AutoLISP subtration error

Using the following code where line1 is a 180d line, the idea is to reduce it to 0 in order to compare it another line that I will
be doing the same thing to.

(setq *pi90* (* pi 0.5))

; to set the angle of the line assume 180d for my porpose
(setq line1_angle (angle (dxf 10 (setq line1_list (entget line1))) (dxf 11 line1_list)))

(while (>= line1_angle *pi90*) (setq line1_angle (- line1_angle *pi90*)))


The problem is that "line1_angle" solves to
1.33227e-015
instead of 0.0.

Is there a reason that this is not solving to 0.00, is this a known issue. Is there some known fix for this?
Thanks
Cliff

 

Yes. The reason is that no computer ever will have enough memory to
store PI in full accuracy. And of course: no oldfashioned
mathematician will ever have enough paper to write down PI to full
accuracy.

There is no difference between computer based math and paper based
math: comparing results of calculations which are based on real
numbers like PI will always have limited accuracy.

Yes, of course.

Compare with EQUAL and a fuzzy value to give a bandwidth for the
accuracy which will fullfill your needs. Something like
(equal PI 3.14 0.01)

Tom Berger