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:

Operations	Matlab Form	Comments
Array Addition	a+b	Array & matrix addition are identical
Array Subtraction	a-b	Array & matrix subtraction are identical
Array Multiplication	a.*b	Array multiplication element by element multiplication of a & b
Matrix Multiplication	a*b	For matrix multiplication no of the column in matrix a=no of column of matrix b
Array Right Division	a./b	Element by element division of a & b
Array Left Division	a.\b	Element by element division of a & b with in the Nr.
Matrix Right Division	a/b	a* inv(b) where inv represent inverse
Matrix Left Division	a\b	inv(a)*b
Array Exponential	a.^b	Element by element exponential of a & b i.e a( i , j) ^ b( i , j)