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Mathematica® Teacher's Edition (2002)

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17.3 Getting Pieces of Matrices

Ways to get pieces of matrices.

Matrices in Mathematica TE are represented as lists of lists. You can use all the standard Mathematica TE list-manipulation operations on matrices.

Here is a sample matrix.

In[1]:= MatrixForm[t = Array[a, {3, 3}] ]

Out[1]//MatrixForm=

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]:= Transpose[t][[2]]

Out[3]=

This way of picking out a submatrix is convenient when you deal with bigger matrices.

In[4]:= MatrixForm[ t[[ Range[1,2], Range[2,3] ]] ]

Out[4]//MatrixForm=

This picks out the four corners of the matrix.

In[5]:= MatrixForm[ t[[ {1, 3}, {1, 3} ]] ]

Out[5]//MatrixForm=