Central numerical differentiation - Error

Hello everyone,

I'm trying to implement the numerical differentiation by using central method:

%             x[k+1] - x[k-1]
% x_dot [k] = ---------------- = (x[k+1] - x[k-1])*sr/2
%                  2*Ts

I wrote the code:

sr = 0.1;
a = 0:0.001:10;
t = a;
b = ( a(2:end) - a(1:end) ) * sr/2;
plot(t,a)
hold on
plot(t,b)

but it does not work; in particular, the statement "b = ( a(2:end) - a(1:end) ) * sr/2;" is wrong.

Is it possible to reach my goal by fixing the above statement? I prefer to avoid to insert additional code lines.

Thank you so much in advance.

Answer 1

[Image Analyst]

Instead of that, use the diff() function

b = diff(a) * sr/2;

[Gennaro Arguzzi]

Hello @ImageAnalyst, I kown that diff() carries out the difference a[k+1]-a[k]; this shoul be the forward numerical differentiation, instead I need the central numerical differentiation.

[Image Analyst]

Try a simple for loop

for k = 2 : length(a)-1
    theDiff = a(k+1) - a(k-1);

etc.

[Gennaro Arguzzi]

Thank you @ImageAnalyst.