3.7.1 Constructing Matrices
Functions for constructing matrices. This generates a  matrix whose   entry is a[i, j].
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Here is another way to produce the same matrix.
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DiagonalMatrix makes a matrix with zeros everywhere except on the leading diagonal.
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IdentityMatrix[n] produces an  identity matrix.
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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.
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This gives a tridiagonal matrix.
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MatrixForm prints the matrix in a two-dimensional array, and makes the structure in this case clearer. Out[7]//MatrixForm=
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