# how i can compute a signal derivative inside MATLAB function block without extra blocks

17 views (last 30 days)
khalil youcefa on 27 Oct 2016
Edited: khalil youcefa on 28 Oct 2016
I am feeding a signal q into a MATLAB Function block - for example a sinusoid (it could be something else too). My MATLAB Function block also needs the time derivative of the signal. In Simulink I can do something like this:
my question is: How do I get qdot inside MATLAB Function without using any extra blocks (and removing the Derivative block above obviously)?

Swarooph on 27 Oct 2016
1. I would like to point out the fact that the derivative block has its limitation. Please refer to the documentation page here.
2. Note from the documentation that, all it does is calculate change in input over change in time. You can do that using a combination of Memory and Clock blocks. Screenshot and code below.
function [y,ydot] = fcn(q,qdel,t,tdel)
y = q; %First output is the input signal itself
delT = t - tdel; % Calculate time interval
delU = q - qdel; % Calculate signal change
if delT > 0 % Check if it is not the first time step
ydot = delU/delT; % Calculate change in input over change in time
else
ydot = 0; % Arbitrarily set derivative to 0 if it is the first time step
end
end

#### 1 Comment

khalil youcefa on 28 Oct 2016