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version 6.0
SET REAL COMPARISON LEVEL (epsilon)
| Parameter | Type | Description | |
| epsilon | Number |  | Epsilon value for real equality comparisons |
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.
Note: If you want to execute a query or an "Order by" on a numeric indexed field whose values are lower than 10^-6, make sure that the SET REAL COMPARISON LEVEL command is executed before construction of the index.
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.
See Also
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