Fortran和Python之间的精度差异（sin函数） [英] Precision discrepancy between Fortran and Python (sin function)

问题描述

使用正弦函数时，我发现python和Fortran之间存在差异。任何人都可以谈谈这个问题吗？

in python：

  import math 
 print（math.sin（6.28318530717959））
>> 3.9077843189710302e-15 
  

在fortran90中：

  print *，sin（6.28318530717959d0）
>>编辑：
编辑：
因为它似乎是一个Fortran编译器问题，所以我使用g95和
 
 $ p $ g $ -O3 test.f90 -o test.exe 
  

解决方案

根据IEEE 754的浮点表示法：

pre $ In [7]：bin（3.3077720792452914e-15.view（np.uint64））
Out [7]：'0b11110011101101110010110011010000000000000000000000000000000000 '


显示截尾尾数，当

<$在[9]：bin（3.3077843189710302e-15.view（np.uint64））
Out [9]：'0b11110011101101110010110011101100111001100111010111010001111111'

可能是一个类型问题，其中float32在过程，甚至起源都是神秘的。

I see a discrepancy between python and Fortran when using the sinus function. Could anyone shed light on this, please?

in python:

      import math
      print(math.sin(6.28318530717959))
      >> 3.3077843189710302e-15

in fortran90:

      print*, sin(6.28318530717959d0)
      >> 3.3077720792452914E-15

---

EDIT: As it seems to be a Fortran compiler issue, I used g95 with

       g95 -O3 test.f90 -o test.exe

解决方案

According to IEEE 754 for float representation:

In [7]: bin(3.3077720792452914e-15.view(np.uint64))
Out[7]: '0b11110011101101110010110011010000000000000000000000000000000000'

shows a truncated mantissa, when

In [9]: bin(3.3077843189710302e-15.view(np.uint64))
Out[9]: '0b11110011101101110010110011101100111001100111010111010001111111'

shows a plain one.

Probably a type issue, with a float32 in the process, even the origin is mysterious.

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