Take the 2-minute tour ×  Sometimes when I invoke FullSimplify
on a large expression, I get a series of messages like this:
FullSimplify::ztest1 "Unable to decide whether numeric quantity
«1» is equal to zero. Assuming it is."  I suppose Mathematica
makes this assumption when numeric calculations with reasonably
high precision do not produce a number that can be distinguished
from the exact 0. While in certain cases this is useful, I want
to be able to disable this assumption in cases that I believe
involve tiny non-zero quantities.  Is it possible to disable
this kind of assumption in FullSimplify?  share|improve this
question Perhaps FullSimplify is using PossibleZeroQ. You may
try to override it –  belisarius Nov 28 '13 at 4:29 It will nice
if one can have a small example also. –  Nasser Nov 28 '13 at
4:44 I think @belisarius is correct. The working of
PossibleZeroQ is controllable via the system options
AlgebraicsOptions -> AlgebraicZeroTestParameters,
ZeroTestMaxPrecision, and ZeroTestNumericalPrecision