While Matlab employs variables it does not use a Type
Definition or a Dimension
Statement.
If it comes across a new variable name it
automatically creates it. In MATLAB
workspace at Matlab prompt
(>>) Type the following and hit return at
end of line
a = 1.0; b = 2, c = 3.0; d = 4.0; e
= 5.0; (return)
one = a; two = b; three = c, four = d, five
= e; six = pi; (return)
who
A = [a b c; d e pi] %
This is a 2 X 3 matrix
% The semicolon seperates the rows
% The space seperates the array elements
B = A'
% B is the transpose of A
C = A*B
% A consistent matrix multiplication
D = A*C
% An inconsistent matrix multiplication
- should see an error
D = B*C
help inverse % inverse
is not a MATLAB command
lookfor inverse %
looks for the word inverse in all the files
% looks like INV is the command we need
% note: in help INV is capitalized - inuse it
% must be lower case
help inv
Dinv = inv(D)
Cinv = inv(C)
variable type and storage
are assigned in context or on
initiation
variable names are case sensitive
variable names start with a letter and can
contain upto 31 characters which include
letters, digits and underscore ( punctuation characters are
not allowed)
To know what is stored in a variable type its name
at the command prompt
At the Matlab prompt :
D %
should see what is in D
Matlab has built in variable names.
the following are some of the built in variables:
ans, pi, eps, flops, inf,
NaN or nan, i , j, nargin, nargout, realmin, realmax.
Avoid using built-in names.
MATLAB uses conventional decimal notation, with an optional decimal point
and leading plus or minus sign, for numbers.
1
-9 +9.0
0.001 99.098765
Scientific notation uses the letter e to specify a power-of-ten scale factor.
2.0e-03
1.07e23 -1.732e+03
Imaginary numbers use either i or j as a suffix.
1i
-3.1415j
3e5i
All numbers are stored internally using the long format specified by the
IEEE floating-point standard. Floating-point numbers have a finite precision
of roughly 16 significant decimal digits and a finite range of roughly
10-308 to 10+308. (This is sometimes operating system dependent).
However all numbers are displayed differently depending on the context
and precision
MATLAB performs all computations in double precision. The format
command described below switches among different display formats.
Command
Result
Example
format
Default.
Same as short
format
short 5 digit scaled fixed point
3.1416
format
long 15 digit scaled fixed point
3.14159265358979
format
short e 5 digit floating-point
3.1416e+00
format
long e 15 digit floating-point
3.141592653589793e+00
format
short g Best of 5 digit fixed or floating
3.1416
format
long g Best of 15 digit fixed or floating
3.14159265358979
format
hex Hexadecimal
400921fb54442d18
format
bank Fixed dollars and cents
3.14
format
rat Ratio of
small integers
355/113
format
+
+,-,
+3.1416
format
compact Suppresses excess line feeds.
format
loose Add line feeds.
format compact
aa = 1 %
an integer
ab = 1.0 %
a real value - note both aa and ab are displayed the same way
format long
aa
ab
% still same display as before
aa = aa * 1.23 % note
the long representation and automatic type conversion
ab = ab*1.23 % same
format short
who % lists
all your variables
size(A) % should return
matrix dimensions
% size() is a Matlab built-in function
SizeB = size(B) % what
happened here ?
% SizeB is an array variable which contains the
% information returned from using the size(B)
% on the right
SizeB(1)
% returns the number of rows of B
AB = [A B] % a
new Matrix AB by joining A and B
% should see an error
AB = [ A B'] % a new
2 X 6 matrix
AB(:,3)
% returns the 3 rd column of AB
AB(2,:)
% returns the 2 nd row of AB
ABStack = [AB ; AB] % stack Ab on
top of itself
ABStack(2,2) = 10.0 %
change the 2,2 element to 10.0 from 5.0
We will visit
Matlab functions next
