MATLAB Variables

Objective: To study data types, constant and variable, character, operators, assignment statement. To consider vectors and matrices commands to operate on vectors and matrices, matrices manipulation.

Variables: MATLAB variable is a region of memory containing an area which is known by the user-specified name.

These are of two types:

• double: - 64 bit (10^-308 to 10^308 with 15 to 16 significant decimal digits).
  

  e.g:
  var=10.5  //Real value
  var=10i , var=-4j //Imaginary value 
  var=10+10i

• char: - 16 bit (-32768-32767)
  

  e.g:
  var='This is a character string';

Initialization of a variable:

• Assignment statement: It is simplest and used for small arrays.
              Var=expression;
  Where var is name and expression are a scaler constant, an array or a combination of constraints, other variables, and mathematical operations.
  The number of elements in every row must be same. Also, the number of elements in every column must be the same.

            >> var= [3.4]        //creates a 1x1 array with value 3.4
                         var = 3.4000

            >> var= [1.0 2.0 3.0]  // creates a 1x3 array with value [1 2 3] 
                         var=1 2 3

              >> var= [1.0;2.0;3.0]  // creates a 3x1 array 
                           var =    1
                                        2
                                        3
                >> var= [1,2,3;4,5,6]  //creates a 2x3 array
                             var =   1     2     3
                                        4     5     6
                >> var= [1,2,3
                               4,5,6]    //creates a 2x3 array
                              var =  1     2     3 
                                         4     5     6
                  >> var= []     //creates an empty array 
                               var = []
                  >> var1= [0 1+7]
                                 var1 = 0     8
                  >> var2=[var1(2) 7 var1]
                              var2 =  8     7     0     8
                  >> var3(2,3) =5
                              var3 = 0     0     0
                                         0     0     5
                  >> var3(3,3) =6
                                   var3 =0     0     0
                         0      0     5
                                             0     0     6

• Shortcut expressions:

>> x= [1:2:10]
        x =    1     3     5     7     9

Shortcuts can be combined with the transpose operator (') to initialize column vectors.

               >> f= [1:4]'
                        f =1
                            2
                            3
                            4
               >> g=[1:4]
                         g =1     2     3     4
             >> h=[g',g']
                        h =1     1
                             2     2
                             3     3
                         4     4

• Built in functions:
  Zeros:

                  >> a=zeros (2)
                            a =0     0
                                 0     0
                >> b=zeros (2,3)
                           b = 0     0     0
                                 0     0     0

               >> c= [1,2;3,4]
                        c =1     2
                             3     4
 
              >> d=zeros(size(c))

                        d =     0     0
                                  0     0

Ones: 0's are replaced by 1's

               >> f=ones (4)
                        f =     1     1     1     1
                                 1     1     1     1
                                 1     1     1     1
                                 1     1     1     1

Eyes: to generate arrays containing identity matrices in which all on-diagonal element is 1 while all off-diagonal element is 0.

                >> e=eye(4)
                           e =     1     0     0     0
                                     0     1     0     0
                                     0     0     1     0
                                     0     0     0     1

• Keyboard input:input funcn
  • var=input ('enter a input value')
  • enter a input value
  • var=input ('enter data','s')
  • enter data 3
    var =3
• Multidimensional array
  • c(:,:,1) =[1 2 3;4 5 6]
  • c =       1       2       3
          4       5       6
  • c(:,:,2) = 7       8       9
          10       11       12
• STORING MULTIDIMENSIONAL ARRAY IN MEMORY
  

  •	Eg: a= [1 2 3;4 5 6;7 8 9;10 11 12]
  a =
                 1     2     3
                 4     5     6
  7	 8     9
    10    11    12

• Subarray
  

  •	arr= [1 2 3;-2 -3 -4;3 4 5]
              arr =  1     2     3
                       -2    -3    -4
                         3     4     5
  	arr1(1,:)=[1 2 3]
  •	arr1 =     1     2     3

• End func:

  •	arr=[1 2 3 4 5 6 7 8];
  •	>> arr(5:end)
            ans =  5     6     7     8
  •	>> arr(1:2,[1,4])=[20 21 ;22 23]
            arr =
  20	   2     3    21     5     6     7     8
      22     0     0    23     0     0     0     0
  
  •	>> arr=[1 2 3 4 ;5 6 7 8;9 10 11 12];
  •	>> arr(1:2,1:2)=1
            arr =
       1     1     3     4
       1     1     7     8
       9    10    11    12

• Predefined specific values:
  • pi: It contains values up to 15 significant digits
  • inf: infinity
  • nan: not a number
  • clock: current date & time in the form of 6 element vector containing
    year, month, datemin and second
  • date: current date in a character string format eg:24-Jan-2019
  • eps:Esiton i.e smallest difference b/w two no's
  • ans: It used to store the result of an expression
• Displaying Output Data:
  • Disp fn: It accepts an array of arguments & shows the value of the array in the command
    

         window
         str=['the value of pi='num2str(pi)];
         disp(str);

• Formatted Output Function With fprintf Function:
  • Display one or more values together with related text & lets the programmer to control the way the display value appears
  • Syntax: fprintf(format,data);
  • Eg:fprintf('the value of pi=%f\n',pi);
    fprintf('the value of pi=%d\n',pi);
    fprintf('the value of pi=%e\n',pi);
• Scalar Operations:
  

  •	E.g.: =2^ ((8+2)/5)
           =26(10/5)
           =2^2
           =4

• Array Operations:
  

           z=1             
      >> z
           z =1     2
                3     4
  
  >> y=-1
           y = -1
  
       >> y
            y =-1     3
                 -2      0
  
                    >> y+z
  ans =
       0     5
       1     4

• Matrix Operation based on Linear Algebra: