add read me

venv/lib/python3.12/site-packages/sympy/matrices/benchmarks/bench_matrix.py

@@ -0,0 +1,21 @@
+from sympy.core.numbers import Integer
+from sympy.matrices.dense import (eye, zeros)
+
+i3 = Integer(3)
+M = eye(100)
+
+
+def timeit_Matrix__getitem_ii():
+    M[3, 3]
+
+
+def timeit_Matrix__getitem_II():
+    M[i3, i3]
+
+
+def timeit_Matrix__getslice():
+    M[:, :]
+
+
+def timeit_Matrix_zeronm():
+    zeros(100, 100)