我如何使PHP的COS功能返回正确的价值？ [英] How can i make the php cos function return the correct value?

问题描述

$ b

  $ x = cos（deg2rad（$ angle））; 
  

但是当角度为90度而不是0时，它返回6.12323399574E-17。
我读了这是一个浮点问题，但是有一个解决方法？

解决方案

6.1E-17几乎是零[*]。如果您需要实际比较结果为零，在浮点数学中，您应该检查它是否在所需值的某个容差范围内，因为大多数数字无法正确表示。

  $ x = cos（deg2rad（$ angle））; 
 $ is_zero =（abs（$ x）< 1e-10）; 
  

严格来说，零实际上是一个可以 的数字在浮点上正确表示。真正的问题是 pi / 2.0 不能这样，所以 cos 函数的输入不是正确的。

[*]为了说明这一点，以1 AU（从太阳到地球的平均距离）的比例来看，相当于0.0092 毫米，或者关于人发的平均宽度的十分之一 ...

I've tried

$x = cos(deg2rad($angle));

but it returns 6.12323399574E-17 when the angle is 90 degrees instead of 0. I read that this is a floating point problem, but is there a workaround?

解决方案

6.1E-17 is almost zero anyway[*]. If you need to actually compare the result to zero, in floating point math you should check that it's within a certain tolerance of the desired value, since most numbers can't be represented correctly.

$x = cos(deg2rad($angle));
$is_zero = (abs($x) < 1e-10);

Strictly speaking, of course, zero is actually a number that can be represented correctly in floating point. The real problem is that pi / 2.0 can't be, so the input to your cos function isn't "correct".

[*] To put that in context, taken as a proportion of 1 AU (the average distance from the Sun to the Earth) it is equivalent to 0.0092 millimeters, or about a tenth of the average width of a human hair...

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