为什么我在Perl中减去同一个浮点数的时候得不到零呢？ [英] Why don't I get zero when I subtract the same floating point number from itself in Perl?

问题描述

可能存在重复：



为什么ghci说1.1 + 1.1 + 1.1> 3.3是真的？

 ＃！/ usr / bin / perl 
 $ l1 =0 + 0.590580 + 0.583742 + 0.579787 + 0.564928 + 0.504538 + 0.459805 + 0.433273 + 0.384211 + 0.3035810; 
 $ l2 =0 + 0.590580 + 0.583742 + 0.579788 + 0.564928 + 0.504538 + 0.459805 + 0.433272 + 0.384211 + 0.3035810; 
 $ val1 = eval（$ l1）; 
 $ val2 = eval（$ l2）; 
 $ diff =（（$ val1  -  $ val2）/ $ val1）* 100; $（$ val1  -  $ val2）/ $ val1）* 100 ==> $ diff \ n; 
  

令人惊讶的是，输出结果是
<$ （（4.404445 - 4.404445）/4.404445）* 100 ==> -2.01655014354845e-14。

是不是应该是ZERO？
任何人都可以解释这个请求......

解决方案

每个计算机科学家应该知道什么是浮点运算

<为什么C＃中的浮点运算不精确？

这不是Perl相关的，而是浮点相关的。

Possible Duplicates:
Why is floating point arithmetic in C# imprecise?
Why does ghci say that 1.1 + 1.1 + 1.1 > 3.3 is True?

#!/usr/bin/perl
$l1 = "0+0.590580+0.583742+0.579787+0.564928+0.504538+0.459805+0.433273+0.384211+0.3035810";
$l2 = "0+0.590580+0.583742+0.579788+0.564928+0.504538+0.459805+0.433272+0.384211+0.3035810";
$val1 = eval ($l1);
$val2 = eval ($l2);
$diff = (($val1 - $val2)/$val1)*100;
print " (($val1 - $val2)/$val1)*100 ==> $diff\n";

Surprisingly the output ended up to be

((4.404445 - 4.404445)/4.404445)*100 ==> -2.01655014354845e-14.

Is it not supposed to be a ZERO???? Can any one explain this please......

解决方案

What every computer scientist should know about floating point arithmetic

See Why is floating point arithmetic in C# imprecise?

This isn't Perl related, but floating point related.

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