Double.Equals Method (Object)
Returns a value indicating whether this instance is equal to a specified object.
Assembly: mscorlib (in mscorlib.dll)
The Equals method should be used with caution, because two apparently equivalent values can be unequal due to the differing precision of the two values. The following example reports that the Double value .3333 and the Double returned by dividing 1 by 3 are unequal.
Rather than comparing for equality, one recommended technique involves defining an acceptable margin of difference between two values (such as .01% of one of the values). If the absolute value of the difference between the two values is less than or equal to that margin, the difference is likely to be due to differences in precision and, therefore, the values are likely to be equal. The following example uses this technique to compare .33333 and 1/3, the two Double values that the previous example found to be unequal.
' Initialize two doubles with apparently identical values Dim double1 As Double = 0.33333 Dim double2 As Object = 1 / 3 ' Define the tolerance for variation in their values Dim difference As Double = Math.Abs(double1 * 0.0001) ' Compare the values ' The output indicates that the two values are equal If Math.Abs(double1 - CDbl(double2)) <= difference Then outputBlock.Text &= "double1 and double2 are equal." & vbCrLf Else outputBlock.Text &= "double1 and double2 are unequal." & vbCrLf End If
In this case, the values are equal.
Because Epsilon defines the minimum expression of a positive value whose range is near zero, the margin of difference between two similar values must be greater than Epsilon. Typically, it is many times greater than Epsilon.
The precision of floating-point numbers beyond the documented precision is specific to the implementation and version of the .NET Framework. Consequently, a comparison of two particular numbers might change between versions of the .NET Framework because the precision of the numbers' internal representation might change.
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