R minimal calculation error

Hi,

I'm doing some easy calculations to normalize some values. This looks like
this:

x=mean(a+b+c+d ...)
a=a-x
b=b-x
c=c-x
d=d-x
...
mean(a+b+c+d ...) ---> Should now be 0!
However, I'm getting results like -2.315223e-18
This is really near to 0 but not very aesthetic.

Can I prevent this? Or is this behaviour desired?

Hi.

This is a consequence of the limited precision, which is used
for speed. Examples of this type exist also for the decimal
arithmetic. Using 3 digit precision, the arithmetic mean of
the three numbers 1.02, 1.01, 1.01 is 1.01. So, the sum of the
differences

  1.02 - 1.01
  1.01 - 1.01
  1.01 - 1.01

is not zero.

See functions zapsmall(), all.equal().

Hope this helps.

Petr Savicky.