Question

8. In MATLAB, the colon operator can be used in two ways: creating a matrix (or array) and selecting part(s) of a matrix (or array). Explain and give examples of each.

9. For a matrix C, that has 10 rows and 12 columns:

- What is the MATLAB command to select all of row 5 from it?

- What 2 MATLAB commands would ask the user for an integer, N, from 1 to 10 and then create an array D which is just row N from matrix C?

10. For matrix D, that has 5 rows and 8 columns:

- What does the MATLAB command Z=sum(D) do and what is the size (or dimensions) of Z?

Answer 1

(8)   
   In Matlab, colon operator can be used in two ways:
  
   Way 1:   Creating a matrix(or array)
         
       1.   Statement a:b creates a vector from a to b.
       2.   Statement a:k:b creates a vector from a to b at an increment of k
      
   Example:   Creating a matrix of dimension 3x5

      >> m = [1:5 ; 6:10 ; 11:15]
       m =

          1    2    3    4    5
           6    7    8    9   10
           11   12   13   14   15

       >>
      
      
   Way 2:   Selecting parts of array

      mat(:,j)   ->   Returns j th column.
       mat(i,:)    ->   Returns i th row.
       mat(:,:)    ->   Returns entire matrix.
      
       >> m(:,:)
       ans =

           1    2    3    4    5
           6    7    8    9   10
           11   12   13   14   15

       >>
       >> m(1,:)
       ans =

       1   2   3   4   5

       >> m(:,4)
       ans =

       4
       9
       14

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(9)
   Creating a sample matrix C, that has 10 rows and 12 columns:
  
   >> C = randi(10,10,12);
  
  
   MATLAB command to select all of row 5 from it:
  
   C(5,:)
  
   Fetches entire fifth row
  
   Two MATLAB commands would ask the user for an integer, N, from 1 to 10 and then create an array D which is just row N from matrix C:
  
   Asking user for integer N:
  
   N = input(' Enter N value (1 to 10) : ');
  
   Creating an array D which is just row N from matrix C:
  
   D = C(N,:)

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(10)
  
   Creating a sample matrix D, that has 5 rows and 8 columns:
  
   >> D = randi(10,5,8);
  
   Command Z=sum(D); calculates sum of each column values in array D and stores the result as column in Z.
  
   Size (or dimension) of Z can be found using command size(Z); which returns 1 row and 8 columns.