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3.7.2 Getting Pieces of Matrices
Ways to get pieces of matrices.
Matrices in Mathematica are represented as lists of lists. You can use all the standard Mathematica list-manipulation operations on matrices.
Here is a sample 
matrix.
In[1]:= t = Array[a, {3, 3}]
Out[1]= 
This picks out the second row of the matrix.
In[2]:= t[[2]]
Out[2]= 
Here is the second column of the matrix.
In[3]:= Map[#[[2]]&, t]
Out[3]= 
This picks out a submatrix.
In[4]:= t[[ {1, 2}, {2, 3} ]]
Out[4]= 
Here is another way to specify the submatrix, convenient when you deal with bigger matrices.
In[5]:= t[[ Range[1,2], Range[2,3] ]]
Out[5]= 
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