isZero(): test for zero

isZero(x) returns whether x is zero. It is particularly useful before division, normalization, matrix inversion, and logic that treats the origin as a special case.

Prevent invalid operations

Test a denominator before division, and test a determinant before inv(). For sign classification, combine it with isPositive() and isNegative(). abs() helps formulate tolerance checks.

Exact versus approximate zero

Computed decimal values can be close to zero without equaling it exactly. In measurement and floating-point models, compare the magnitude to a chosen tolerance instead of relying only on exact equality.