使用math.round比较数字 [英] Compare numbers using math.round

问题描述

我使用VB.Net比较两个小数最多4位小数。



Dim Num1为Double = 12.34562

Dim Num2 as Double = 12.34567



问题（1）以下哪种方法使用正确：



''----------------------------------------- -



如果Math.Round（Num1,4）> = Math.round（Num2,4）那么

...

结束如果



''-----或者-----



Private AccuracyValue As Double = 0.0001



如果Math.Abs​​（Num1 - Num2）< = AccuracyValue那么

.. 。

结束如果



''--------------------- ----------------------



否则，比较两个数字的正确方法应该是什么在准确度范围内？



问题（2）如果这两个数字是什么
12.3456789和
/>
12.3456782



小数部分为mu ch大于所需的精度。

使用Math.Round会安全吗？



我尝试过：



如果Math.Round（Num1,4）> = Math.round（Num2,4）那么

...

结束如果

I am using VB.Net to compare two numbers upto 4 decimal places.

Dim Num1 as Double = 12.34562
Dim Num2 as Double = 12.34567

Question (1) Which of these methods would be correct to use:

''------------------------------------------

If Math.Round(Num1, 4) >= Math.round(Num2, 4) Then
...
End If

''----- OR -----

Private AccuracyValue As Double = 0.0001

If Math.Abs(Num1 - Num2) <= AccuracyValue Then
...
End If

''-------------------------------------------

Else, what should be the correct way to compare two number within a accuracy range ?

Question (2) What if the two numbers are
12.3456789 and
12.3456782

where the decimal part is much larger than the required accuracy.
Will using Math.Round be safe ?

What I have tried:

If Math.Round(Num1, 4) >= Math.round(Num2, 4) Then
...
End If

推荐答案

1）
比较差异的绝对值与数量值（通常表示为ε - 小希腊字母epsilon）是常用方法：

1) Comparing the absolute of the difference with a quantity value (often denoted ε - small greek letter epsilon) is the common method:

diff = num1 - num2
if (abs(diff) <= epsilon)
    # numbers are similar
else
    # may use sign of diff here to check if larger or smaller

这种方法也比比较舍入值快得多。



2）

忽略其他数字。在您的示例中，两个值都将四舍五入为 12.3457 。

This method is also much faster than comparing rounded values.

2)
Additional digits are ignored. With your example, both values will be rounded to 12.3457.

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