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156 GNU Octaveargument is optional, and specifies how many diagonals above or below the maindiagonal should also be set to zero.The default value of k is zero, so that triu and tril normally include the maindiagonal as part of the result matrix.If the value of k is negative, additional elements above (for tril) or below (for triu)the main diagonal are also selected.The absolute value of k must not be greater than the number of sub- or superdiagonals.For example,tril (ones (3), -1)⇒ 0 0 01 0 01 1 0andtril (ones (3), 1)⇒ 1 1 01 1 11 1 1vec (x)Function FileReturn the vector obtained by stacking the columns of the matrix x one above theother.vech (x)Function FileReturn the vector obtained by eliminating all supradiagonal elements of the squarematrix x and stacking the result one column above the other.prepad (x, l, c)Function Filepostpad (x, l, c)Function Filepostpad (x, l, c, dim)Function FilePrepends (appends) the scalar value c to the vector x until it is of length l. If thethird argument is not supplied, a value of 0 is used.If length (x) > l, elements from the beginning (end) of x are removed until a vectorof length l is obtained.If x is a matrix, elements are prepended or removed from each row.If the optional dim argument is given, then operate along this dimension.18.3 Special Utility Matriceseye (x)Built-in Functioneye (n, m)Built-in Functioneye (..., class)Built-in FunctionReturn an identity matrix. If invoked with a single scalar argument, eye returnsa square matrix with the dimension specified. If you supply two scalar arguments,