Perl：如何比较浮点数 [英] Perl: How to compare floating numbers

问题描述

我写了下面的Perl脚本。但是，它不打印1。我做了一些研究，似乎是因为浮点数的IEEE表示。那么，有没有更好的方法来比较Perl中的浮点数？

$ p $ for（my $ tmp = 0.1; $ tmp < = 1; $ tmp + = 0.05）{print $ tmp。\\\
}


输出：

  0.1 
 0.15 
 0.2 
 0.25 
 0.3 
 0.35 
 0.4 
 0.45 
 0.5 
 0.55 
 0.6 
 0.65 
 0.7 
 0.75 
 0.8 
 0.85 
 0.9 
 0.95 
  

解决方案

使用浮点数的所有计算都可能有精度错误，如果重复使用这些结果，那么这些精度错误就会叠加起来。有一点要学习，就是永远不要使用float作为循环控制变量。

使用类似于

的

<$对于（my $ tmp = 2; $ tmp< = 20; tmp ++）{
print $ tmp / 20.0，\\\
; p $ p>
}


尽你所能。如果你真的需要比较两个浮动（$ a，$ b）类似于

  if（abs（$ a  -  $ b）< 0.000001）
  

只有真正有效的东西 - 但是，这也可能有问题，取决于差异可以算作一个真正的差异有多小。

I wrote the following Perl script. However, it does not print "1". I did some research and it seems it is because of the IEEE representation of floating-point number. So, is there a better way to compare floating-point numbers in Perl?

for (my $tmp = 0.1; $tmp <= 1; $tmp+=0.05){print $tmp."\n"}

Output:

0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95

解决方案

All computations that use floating point numbers may have precision errors, and if you reuse the results, those precision erros stack up. One thing to learn from that is to never use a float as a loop control variable.

Use something like

for (my $tmp=2; $tmp<=20; tmp++) {
    print $tmp/20.0, "\n";
}

whereever you can. If you really really need to compare two floats ($a, $b) something like

if (abs($a - $b) < 0.000001)

is the only thing that really works -- however, this might have issues as well depending on how small the difference can be to count as a real difference.

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