why is this code showing zero for all equations??

disp('Enter all values in row vector ');
x=input('Enter the values of x=');
y=input('Enter the values of function at x f(x)=');
val=input('Enter the value of x at which derivative is to be calculated=');
i=find(x==val);
fd=[y(i+1)-y(i)]/[x(i+1)-x(i)];
cd=[y(i+1)-y(i-1)]/[x(i+1)-x(i-1)];
bd=[y(i)-y(i-1)]/[x(i)-x(i-1)];
disp('Following are the Difference Derivatives')
disp('  FDD     CDD     BDD')
disp([fd             cd              bd])

Answer 1

[KALYAN ACHARJYA]

Enter the val value such that it must contain in x, then only following give some non zero value

i=find(x==val);

Other wise If you enter like as follows

Enter all values in row vector 
Enter the values of x=[1 2 3 4]
Enter the values of function at x f(x)=[1 2 4 5]
Enter the value of x at which derivative is to be calculated=6

Now form the next statemnet

i=find(x==val); 

Find in x, which equal to 6, actually 6 is not there, hence it return null

>> whos i
  Name      Size            Bytes  Class     Attributes

  i         1x0                 0  double   

which leads to zero in the equations.

Following gives non zero result, where I have choose val=2, which is part of x vector.

Enter all values in row vector 
Enter the values of x=[1 2 3 4]
Enter the values of function at x f(x)=[1 2 4 5]
Enter the value of x at which derivative is to be calculated=2
Following are the Difference Derivatives
  FDD     CDD     BDD
    2.0000    1.5000    1.0000

Hope it Helps!