4D v13.4SET REAL COMPARISON LEVEL |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
4D v13.4
SET REAL COMPARISON LEVEL
|
SET REAL COMPARISON LEVEL ( epsilon ) | ||||||||
Parameter | Type | Description | ||||||
epsilon | Real |
![]() |
Epsilon value for real equality comparisons | |||||
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:
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.
Product: 4D
Theme: Math
Number:
623
Created: 4D v6