setRealComparisonLevel
setRealComparisonLevel ( epsilon : number )
| Parameter | Type | Description | |
|---|---|---|---|
| epsilon | number | → | Epsilon value for real equality comparisons |
Description
The setRealComparisonLevel command sets the epsilon value used by Qodly 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. Qodly 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, Qodly 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 setRealComparisonLevel, you can increase or decrease the epsilon value as you require.
The command will have no effect if epsilon > 10^-3 or if epsilon < 0.
Changing the epsilon only affects real number comparison for equality. It has no effect on other real computations nor on the display of real values.
This command should be used in specific cases, such as sorting on an attribute with values less than 10^-6. Usually, you will not need to change the default epsilon value.
The setRealComparisonLevel command has no effect on queries and sorts performed with attributes of the Number type. It only applies the Qodly language.