如何使用带分数的numpy数组? [英] How to use numpy arrays with fractions?

问题描述

我正在尝试在Python中实现单纯形方法，因此我需要在数组上使用高斯消除.通常会出现分数，为了更清楚，更准确地表示，我想保留分数形式而不是使用浮点数. 我知道分数"模块，但是我在努力使用它.我使用此模块编写了代码，但数组始终以浮点数返回.是否可以打印内部带有分数的数组? 在这个基本示例中:

I'm trying to implement the simplex method in Python so I need to use the Gaussian elimination on arrays. Very often fractions come up and for more clarity and precision I would like to keep the fractional form instead of using floats. I know the 'fractions' module but I'm struggling to use it. I wrote my code using this module but the arrays are always returned with floats. Isn't it possible to print an array with fractions inside ? On this basic example :

>>> A
array([[-1.,  1.],
   [-2., -1.]])
>>> A[0][0]=Fraction(2,3)
>>> A
array([[ 0.66666667,  1.        ],
   [-2.        , -1.        ]])

我想拥有array([[ 2/3, 1. ], [-2. , -1. ]])

I would like to have array([[ 2/3, 1. ], [-2. , -1. ]])

似乎numpy总是切换为浮点数

It seems numpy always switches to floats

推荐答案

由于Fraction不是

Since Fractions are not a native NumPy dtype, to store a Fraction in a NumPy array you need to convert the array to object dtype:

import numpy as np
from fractions import Fraction

A = np.array([[-1.,  1.],
              [-2., -1.]])   # <-- creates an array with a floating-point dtype (float32 or float64 depending on your OS)
A = A.astype('object')
A[0, 0] = Fraction(2,3)
print(A)

打印

[[Fraction(2, 3) 1.0]
 [-2.0 -1.0]]

---

PS.正如 user2357112建议，您最好使用如果您要使用有理数，请 sympy .或者，仅将矩阵表示为列表列表.如果您的数组为object dtype，则使用NumPy没有速度优势.

---

PS. As user2357112 suggests, you might be better off using sympy if you wish to use rational numbers. Or, just represent the matrix as a list of lists. There are no speed advantages to using NumPy if your arrays are of object dtype.

import sympy as sy

A = [[-1.,  1.],
     [-2., -1.]]
A[0][0] = sy.Rational('2/3')
print(A)

打印

[[2/3, 1.0], [-2.0, -1.0]]

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