不正确的浮点数学？ [英] Incorrect floating point math?

问题描述

这是一个问题，这让我完全不知道过去几个小时...

我有一个方程硬编码在我的程序：

  double s2; 
 
 s2 =  - （0 * 13）/ 84 + 6 / 42-0 / 84 + 24/12 +（6 * 13）/ 42; 
 

每次运行程序时，计算机都输出3作为答案，但是做数学更进一步，在将方程输入Matlab之后，我也得到答案4.这里是怎么回事？

我可以想到的唯一的东西那里是错误的，这将是四舍五入的错误。但是，最多有5个舍入误差，加上使用双精度数学，我的最大误差将非常小，所以我怀疑是问题。

任何人能够

$

在C ++中，5/4 = 1， not 1.25 - 因为5和4都是整数，所以结果将是一个整数，因此结果的小数部分抛弃。

另一方面，5.0 / 4.0将等于约。 1.25，因为5.0和4.0中的至少一个是浮点数，因此结果也是浮点数。

Here is a problem that has had me completely baffled for the past few hours...

I have an equation hard coded in my program:

double s2;

s2 = -(0*13)/84+6/42-0/84+24/12+(6*13)/42;

Every time i run the program, the computer spits out 3 as the answer, however doing the math by hand, i get 4. Even further, after inputting the equation into Matlab, I also get the answer 4. Whats going on here?

The only thing i can think of that is going wrong here would be round off error. However with a maximum of 5 rounding errors, coupled with using double precision math, my maximum error would be very very small so i doubt that is the problem.

Anyone able to offer any solutions?

Thanks in advance,

-Faken

解决方案

You're not actually doing floating point math there, you're doing integer math, which will floor the results of divisions.

In C++, 5/4 = 1, not 1.25 - because 5 and 4 are both integers, so the result will be an integer, and thus the fractional part of the result is thrown away.

On the other hand, 5.0/4.0 will equal approx. 1.25 because at least one of 5.0 and 4.0 is a floating-point number so the result will also be floating point.

这篇关于不正确的浮点数学？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！