MATLAB by rudra pratap

3.6 Using Built-in Functions and On-line Help
89
As shown in Fig. 3.7, MATLAB lists all functions that have the string eigenvalue
either in their name or in the first line of their description. You can then browse
through the list, choose the function that seems closest to your needs, and ask for
further help on it. In Fig. 3.7, for example, we seek help on function eig. The
on-line help on eig tells us what this function does and how to use it.
Thus, if we are interested in just the eigenvalues of matrix A, we type eig (A) to
get the eigenvalues, but if we want to find both the eigenvalues and the eigenvectors
of A, we specify the output list explicitly and type [eigvec, eigval] =eig(A) (see
Fig. 3.8) . The names of the output or the input variables can be anything we choose.
Although it's obvious, we note that the list of the variables (input or output) must
be in the same order as specified by the function.
>> A = [5 -3 2; -3 8 4; 4 2 -9} ;
» eig (A)
ans =
-10 .2206
4.4 246
9.7960
>> [eigvec ,eigval]
eigve c =
0.1725
0.2 382
-0 . 9558
0.8706
0.3774
0.3156
eig (A)
-
0 . 5375
0. 8429
Typing eig (A) without a list of
outputs gives the eigenvalues of A
in a column vector stored in the
default output variable ans.
Specifying an explicit list of output
variables [eigvec , eigval) gets
the eigenvectors of A in the matrix
eigvec and the eigenvalues of A on
the diagonal of the matrix eigval.
eigval =
-10 .2206
0
0
0
4.4246
0
0
0
9. 7960
Figure 3.8: Examples of usc of the function eig to find eigenvalues and eigenvectors
of a matrix.
Some comments on the help facility
• MATLAB is case-sensitive. All built-in functions in MATLAB use lowercase
letters for their names, yet the help on any function lists the function in
uppercase letters, as is evident from Figs. 3.5 and 3.7. For the first-time user,