Implementing Difference Equation in MATLAB

[raheequlmakhtoom]

please help me to implement this difference equation in MATLAB?

y[n]=x[n]-x[n-1];

matlab is not supportin -ve index...

 

[LeBrad]

please help me to implement this difference equation in MATLAB?

y[n]=x[n]-x[n-1];

matlab is not supportin -ve index...

Matlab doesn't like negative indexes as you seem to have noticed. But there are at least three easy ways to get around this.

clear

n = [0:100]; N = length(n);
x = cos(n/25);

% option 1
y1(1) = x(1) - cos(-1/25); %compute y(1) first
for i = 2:N
    y1(i) = x(i)-x(i-1);
end
figure;plot(n,y1,n,x)

% option 2
x0 = cos(-1/25); %define x(-1) outside loop
for i = 1:N
    y2(i) = x(i) - x0;
    x0 = x(i);
end
figure;plot(n,y2,n,x)

% option 3
n2 = [-1:99]; % use vectors instead of loop
xn = cos(n/25);
xn_minus_one = cos(n2/25);
y3 = xn-xn_minus_one;
figure;plot(n,y3,n,xn)

If you want to use a loop, you can loop over i=2:N and define y(1) outside of the loop.

Another option is to loop from i=1:N and define x(n-1) as x0 and update it at each step, that way you never try to acces x(-1).

If you don't want to use a loop, you can just create vectors for x[n] and x[n-1] over a big range of n, and just compute y by subtracting those long vectors.

 

[piercas]

To implement this difference equation in MATLAB, you can use the built-in function "diff" which calculates the difference between consecutive elements in a vector. You can use it as follows:

y = diff(x)

This will give you a vector y with the same length as x, where each element is the difference between the corresponding elements in x and x[n-1]. Alternatively, you can also use indexing to shift the elements in x and then perform the subtraction, as shown below:

y = x(2:end) - x(1:end-1)

This will give you the same result as using the "diff" function. Please note that MATLAB does not support negative indexing, so you will need to use positive indices to access the elements in x.