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3.7.1 Constructing Matrices
Functions for constructing matrices.
This generates a  matrix whose   entry is a[i, j].
In[1]:= Table[a[i, j], {i, 2}, {j, 2}]
Out[1]= 
Here is another way to produce the same matrix.
In[2]:= Array[a, {2, 2}]
Out[2]= 
DiagonalMatrix makes a matrix with zeros everywhere except on the leading diagonal.
In[3]:= DiagonalMatrix[{a, b, c}]
Out[3]= 
IdentityMatrix[n] produces an  identity matrix.
In[4]:= IdentityMatrix[3]
Out[4]= 
Of the functions for constructing matrices mentioned above, Table is the most general. You can use Table to produce many kinds of matrices.
Some special types of matrices.
Table evaluates Random[ ] separately for each element, to give a different pseudorandom number in each case.
In[5]:= Table[Random[ ], {2}, {2}]
Out[5]= 
This gives a tridiagonal matrix.
In[6]:= Table[Switch[i-j, -1, a, 0, b, 1, c, _, 0],
{i, 5}, {j, 5}]
Out[6]= 
MatrixForm prints the matrix in a two-dimensional array, and makes the structure in this case clearer.
In[7]:= MatrixForm[%]
Out[7]//MatrixForm= 
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