如何在Sympy中四舍五入Matrix sqrtm？

Question

How to round Matrix elements in sympy?

from sympy import *
from mpmath import *
A=Matrix([[5,4,1],
          [4,6,4],
          [1,4,5]])
print(A)
print(type(A.evalf(3)))
B=sqrtm(A)
print(B)
print(type(B))
print(B.evalf(3))

输出------------------------------------------------ -------------------------------------

Matrix([[5, 4, 1], [4, 6, 4], [1, 4, 5]])

<class 'sympy.matrices.dense.MutableDenseMatrix'>

Traceback (most recent call last):

  File "C:/Users/xxx/.PyCharmCE2018.2/config/scratches/scratch_9.py", line 11, in <module>
    print(B.evalf(3))

AttributeError: 'matrix' object has no attribute 'evalf'

[                 2.0  1.0  3.33606965638267e-20]

[                 1.0  2.0                   1.0]

[3.34095591577049e-20  1.0                   2.0]

<class 'mpmath.matrices.matrices.matrix'>

我想要---------------------------------------------- -----------------------------------------

[2.000  1.000  0.000]

[1.000  2.000  1.000]

[0.000  1.000  2.000]

在此先感谢您，英语不好！

Answer 1

调用sqrtm后，矩阵类型改变，无法使用evalf：

A：<class 'sympy.matrices.dense.MutableDenseMatrix'>

B：<class 'mpmath.matrices.matrices.matrix'>

使用函数chop以漂亮的格式打印矩阵B：

from sympy import *
from mpmath import *
A=Matrix([[5,4,1],
          [4,6,4],
          [1,4,5]])
print(A)
B=sqrtm(A)
print(chop(B))

输出：

[2.0  1.0  0.0]
[1.0  2.0  1.0]
[0.0  1.0  2.0]

另外，您可以玩nprint/nstr。