Graphics Programs Reference
In-Depth Information
The above display illustrates another important point about MATLAB.
Obviously the result of
sum(A)
are the four sums of the elements in the four
columns of
A
. The software prefers working with the columns of matrices. If you
wish to sum all elements of
A
and store the result in a scalar
b
, you simply type
b = sum(sum(A));
which fi rst sums the colums of the matrix and then the elements of the re-
sulting vector. Now we have two variables
A
and
b
stored in the workspace.
We can easily check this by typing
whos
which is certainly the most frequently-used MATLAB command. The soft-
ware lists all variables contained in the workspace together with information
about their dimension, bytes and class.
Name Size Bytes Class
A 4x4 128 double array
ans 1x4 32 double array
b 1x1 8 double array
Grand total is 21 elements using 168 bytes
It is important to note that by default MATLAB is case sensitive, i.e., two
different variables
A
and
a
can be defi ned. In this context, it is recommended
to use capital letters for matrices and lower-case letters for vectors and sca-
lars. You could now delete the contents of the variable
ans
by typing
clear ans
Next we learn how specifi c matrix elements can be accessed or exchanged.
Typing
A(3,2)
simply returns the matrix element located in the third row and second col-
umn. The matrix indexing therefore follows the rule
(row, column)
. We can
use this to access single or several matrix elements. As an example, we
type
A(3,2) = 30
to replace the element
A(3,2)
and displays the entire matrix
A =
2 4 3 7
9 3 -1 2
1 30 3 7
6 6 3 -2
