As you read this
material we strongly recommend that you activate your MATLAB window and try
the commands right there and then
Once you have activated the
command window of MATLAB you can start
declaring variables and entering data.
The declaration part is almost trivial in MATLAB. Everything is assumed to be an array with
dynamic dimensions and dynamic word length.
In other words, if we write: length = 3 , this makes the variable length
a 1X1 array ( a single number). If,
however we write scores = [ 34, 56, 78 ]
, then scores becomes automatically a 1X3 array ( one row , three
columns). Similarly if we write
temperature = [ |
45, |
67, |
87 |
|
35, |
51, |
45 |
|
78, |
40, |
67 ] |
or equivalently temperature = [ 45, 67, 87; 35, 51, 45; 78,
40, 67], then temperature becomes a 3X3 array.
These concepts are illustrated in the picture below:
You must open your MATLAB
window and repeat the above sequence.
You will notice that the system automatically responds ( to the return
button) by printing out the name and value of the variable just entered. One can prevent this immediate display
of the values by placing a semicolon at the end of the definition
statement. Of course, at any point we may print, on demand, any variable we
please by simply typing its name without a semicolon. See the picture below:
Another important point to
notice is this: the whos statement provides a summary of all variables
in use by the program. Note that in our example above all numbers are treated
as doubles, even though they were entered as integers and we did not
specifically ask for double representation.
This “generosity” in memory space makes possible the flexibility of
MATLAB when it comes to declarations.
Everything is treated with the same deep detail. However the output is controlled. We can show as much or as little detail as
we please. By default we get integers
outputted as integers and real numbers by precision 4. To see this, enter in your MATLAB window a
statement like : b = length / 7.1
We can refer to the
individual elements of the arrays using indexes. For example if I need to change the element of temperature which
seats at the second row and third column from 45 to 46.77, I can simply
write temperature(2, 3) = 46.77. Also
we can construct arrays using previously defined arrays. These concepts are shown in the picture
below:
Notice that making a single element of the array
temperature a real number, forces the entire array to be displayed in default
format for real numbers.
The colon operator and
the construction of arrays:
We saw that an array can be
constructed from previously defined arrays.
Another mechanism for easy construction of an array is the colon
operator ( : ) . If we write
a = 2.3 : 0.1 : 2.9
a row array a will be generated which has as first
element 2.3 as last element 2.9 and several elements in between so that the
increase is 0.1. In other words we will
get a = [ 2.3, 2.4, 2.5, 2.6, 2.7, 2.8,
2.9]. See the example below, and
notice what happens if the numbers are not round
We can also use the same
device without the specific increase amount .
Then by default the increment is taken to be one.
See again the example below:
As an extension of this, we
can use the colon operator on array
indices, so that we can indicate
certain subsets of defined arrays. See
the example below: