MATLAB TUTORIAL 3- WORKING WITH MATRIX PART 2

  Hi...friends this is second part of our last article which was MATLAB TUTORIAL 3- WORKING WITH MATRIX PART 1 .......lets continue

Colon operator

The colon operator  will prove very useful and  understanding how it  works is the  key to efficient and convenient usage of MATLAB. It occurs in several different forms.

Often  we must  deal  with  matrices  or  vectors  that   are  too  large  to  enter  one  ele- ment  at  a time.   For  example,  suppose we want  to  enter  a vector  x  consisting  of points (0, 0.1, 0.2, 0.3, · · · , 5). We can use the command

>> x = 0:0.1:5;

The row vector has 51 elements.

Linear spacing

On the  other  hand,  there  is a command  to generate  linearly spaced vectors:  linspace.  It is similar to the colon operator  (:), but  gives direct  control over the number of points.  For

example,

y = linspace(a,b)

generates a row vector y of 100 points linearly spaced between and including a and b.

y = linspace(a,b,n)

generates a row vector y of n points linearly spaced between and including a and b. This is useful when we want to divide an interval into a number of subintervals  of the same length. For example,

>> theta = linspace(0,2*pi,101)

divides the interval [0, 2π] into 100 equal subintervals, then creating a vector of 101 elements.

Colon operator  in  a matrix

The colon operator  can also be used to pick out a certain  row or column.  For example, the statement A(m:n,k:l specifies rows m  to n and column k to l.  Subscript  expressions refer

to portions  of a matrix.  For example,

>> A(2,:)

ans   =

4    5    6

is the second row elements of A.

The colon operator  can also be used to extract  a sub-matrix  from a matrix  A.

>> A(:,2:3)

ans	=
	2	3
	5	6
	8	0

A(:,2:3) is a sub-matrix  with the last two columns of A.

A row or a column of a matrix  can be deleted by setting  it to a null vector, [ ].

>> A(:,2)=[]

ans	=
	1	3
	4	6
	7	0

Deleting row  or  column

To delete a row or column of a matrix,  use the empty  vector operator,  [ ].

>> A(3,:) = []            A  =

1     2      3

4     5      6

Third  row of matrix  A is now deleted.   To restore  the  third  row, we use a technique  for creating  a matrix

>> A = [A(1,:);A(2,:);[7 8 0]]

A	=
	1	2	3
	4	5	6
	7	8	0

Matrix A is now restored  to its original form.

Dimension

To determine  the dimensions  of a matrix  or vector, use the command  size. For example,

>> size(A)

ans    =

3   3

means 3 rows and 3 columns. Or more explicitly with,

>> [m,n]=size(A) 

their are still some operations left so lets continue to PART3