SymPy: Delete multiple rows of a matrix

Question

Is there a method to delete multiple rows of a matrix in SymPy (without using NumPy)?

I understand that .row_del() can only delete one row at a time.

from sympy import *

a_1_1, a_1_2, a_1_3 = symbols ('a_1_1 a_1_2 a_1_3')
a_2_1, a_2_2, a_2_3 = symbols ('a_2_1 a_2_2 a_2_3')
a_3_1, a_3_2, a_3_3 = symbols ('a_3_1 a_3_2 a_3_3')

A = Matrix ([
    [a_1_1, a_1_2, a_1_3], 
    [a_2_1, a_2_2, a_2_3], 
    [a_3_1, a_3_2, a_3_3]
])

A.row_del (1 : 2)

does not (yet?) work:

    A.row_del (1 : 2)
                 ^
SyntaxError: invalid syntax

Answer 1

You can use slicing or outer indexing to select the rows that you want:

In [8]: A = MatrixSymbol('A', 3, 3).as_explicit()

In [9]: A
Out[9]: 
⎡A₀₀  A₀₁  A₀₂⎤
⎢             ⎥
⎢A₁₀  A₁₁  A₁₂⎥
⎢             ⎥
⎣A₂₀  A₂₁  A₂₂⎦

In [10]: A[:1,:]
Out[10]: [A₀₀  A₀₁  A₀₂]

In [11]: A[[0,2],:]
Out[11]: 
⎡A₀₀  A₀₁  A₀₂⎤
⎢             ⎥
⎣A₂₀  A₂₁  A₂₂⎦