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SET REAL COMPARISON LEVEL

SET REAL COMPARISON LEVEL ( epsilon )

ParameterTypeDescription
epsilonReal→Epsilon value for real equality comparisons

This command is not thread-safe, it cannot be used in preemptive code.

Description​

The SET REAL COMPARISON LEVEL command sets the epsilon value used by 4D to compare real values and expressions for equality.

A computer always performs approximative real computations; therefore, testing real numbers for equality should take this approximation into account. 4D does this when comparing real numbers by testing whether or not the difference between the two numbers exceeds a certain value. This value is called the epsilon and works this way:

Given two real numbers a and b, if Abs(a-b) is greater than the epsilon, the numbers are considered not equal; otherwise, the numbers are considered equal.

By default, 4D, sets the epsilon value to 10 power minus 6 (10^-6). Please note that the epsilon value should always be positive. Examples:

  • 0.00001=0.00002 returns False, because the difference 0.00001 is greater than 10^-6.
  • 0.000001=0.000002 returns True, because the difference 0.000001 is not greater than 10^-6.
  • 0.000001=0.000003 returns False, because the difference 0.000002 is greater than 10^-6.

Using SET REAL COMPARISON LEVEL, you can increase or decrease the epsilon value as you require.

WARNING: Typically, you will not need to use this command to change the default epsilon value.

IMPORTANT: Changing the epsilon only affects real comparison for equality. It has no effect on other real computations nor on the display of real values.

Note: The SET REAL COMPARISON LEVEL command has no effect on queries and sorts performed with fields of the Real type. It only applies the 4D language.