No.040 [Python] 무한대 의미의 "inf"

이번에는 무한대를 뜻하는'inf'를 소개해 드리겠습니다.

I'll write about "inf()",which indicates infinity.

■ 부동점 수치flat형 inf

 Floating-point number float-type, "inf"

>>> # コンストラクタ float()の引数に、文字列"inf" を指定
>>> 
>>> f_inf = float("inf")
>>> 
>>> print(f_inf)
inf
>>> 
>>> print(type(f_inf))
<class 'float'>

■ 마이너스의 무한

 Negative "inf"

>>> # infにマイナスをつける
>>> 
>>> f_inf_minus = -float("inf")
>>> 
>>> print(f_inf_minus)
-inf
>>> 
>>> print(type(f_inf_minus))
<class 'float'>

■ 다른 유형으로 바꾸는 방법

 How to change to another type

>>> # infは、int型に変換できない
>>> 
>>> print(int(f_inf))
Traceback (most recent call last):
  File "<pyshell#22>", line 1, in <module>
    print(int(f_inf))
OverflowError: cannot convert float infinity to integer

>>> # ただし、文字列str型は、変換可能
>>> 
>>> print(str(f_inf))
inf
>>> print(type(str(f_inf)))
<class 'str'>

■ inf 만드는 법

 How to create inf

>>> # ① float( )で作成
>>> 
>>> print(float("inf"))
inf
>>> 
>>> print(float("infinity"))
inf
>>> 
>>> print(float('INF'))
inf
>>> 
>>> print(float('INFinity'))
inf
>>> # ↑小文字・大文字混ざっていても問題なし

>>> # ② sysモジュールによる作成
>>> 
>>> import sys
>>> 
>>> f_inf_num = sys.float_info.max * 2
>>> 
>>> print(f_inf_num)
inf

>>> # ③ mathモジュールによる作成
>>> 
>>> import math
>>> 
>>> print(math.inf)
inf
>>> print(type(math.inf))
<class 'float'>
>>> 
>>> print(float("inf") == math.inf)
True

>>> # ④ Numpyによる作成
>>> 
>>> import numpy as np
>>> 
>>> print(np.inf)
inf
>>> 
>>> print(type(np.inf))
<class 'float'>
>>> 
>>> print(float("inf") == np.inf)
True

■ inf가 포함된 연산

 Calculation with "inf"

>>> # 和
>>> 
>>> print(float("inf") + 50)
inf
>>> 
>>> print(float("inf") + float("inf"))
inf

>>> # 差
>>> 
>>> print(float("inf") - 50)
inf
>>> 
>>> print(float("inf") - float("inf"))
nan
>>> # ↑ nanは、非数を表す
>>> 
>>> print(type(float("inf") - float("inf")))
<class 'float'>

>>> # 積
>>> # infに0を掛ける → nan
>>> 
>>> print(float("inf") * 2)
inf
>>> 
>>> print(float("inf") * float("inf"))
inf
>>> print(float("inf") * 0)
nan

>>> # 商
>>> 
>>> # inf を inf で割る → nan
>>> # 0 を inf で割る → 0
>>> # 0 で割る → error
>>> 
>>> print(float("inf") / 2)
inf
>>> 
>>> print(float("inf") / float("inf"))
nan
>>> 
>>> print(float("inf") / 0)
Traceback (most recent call last):
  File "<pyshell#106>", line 1, in <module>
    print(float("inf") / 0)
ZeroDivisionError: float division by zero

>>> # べき乗
>>> # inf の 0乗 → 0
>>> # 1 の inf乗 → 1
>>> # 0 の inf乗 → 0
>>> 
>>> print(float("inf") ** 2)
inf
>>> 
>>> print(float("inf") ** float("inf"))
inf
>>> 
>>> print(float("inf") ** 0)
1.0
>>> 
>>> print(0 ** float("inf"))
0.0
>>> print(2 ** float("inf"))
inf
>>> print(1 ** float("inf"))
1.0

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