I have the following function that returns a nonlinear signal as a function of time:
function y = NARMA_optimized(u,mu,delta,phi,psi,m,N,k)
y = zeros(N,1);
% y(0)=0, and also y(-1)=0 etc.
t = 1;
y(t) = mu.* u(t-m-k).* u(t-k) + delta;
for t = 2:N
v = 1;
for i = 1:m
if t-i > 0 % else we add 0
v = v + y(t-i);
end
end
v = phi.*y(t-1) + v.*psi.*y(t-1) + mu.*u(t-m-k).*u(t-k) + delta;
y(t) = v;
end
end
To call the function, I do the following:
% NARMA Model Comparison
alpha = 0.2;
beta = 0.15;
f_0_i = 1;
delta = 0.1;
Mu = 1.5;
m = 10;
phi = 0.3;
psi = 0.05;
k_shift = 0;
Sigma = 1;
M = 100; % Upper simulation time limit [seconds]
f = @(t) Sigma.*f_0_i.*sin(alpha.*t).*cos(beta.*t);
dt = 10^-2; % timescale step size [seconds]
t_span = [0:dt:M];
T = NARMA_optimized(f,Mu,delta,phi,psi,m,length(t_span),k_shift);
figure;
plot(T);
I would like to change the timescale of the current function to match my discretized representation of time denoted as t_span
.
I know that this will require two key changes in the function:
t=0
, not t=1
.y
by a step size equivalent to dt
, not 1
second. I'm not sure if the current for loop structure can be modified to account for these necessary changes or if I need to start from scratch. I know MATLAB starts at index 1, not index 0. A workaround for "starting" at index 0 in loops is the following:dt = 10^-2; % [seconds]
M = 100; % [seconds]
t_span = [0:dt:M];
for t=1:numel(t_span)
y(t) = [insert value here]
end
I'm not sure if this is they best way to account for dt
and starting at index 0 in the new function.
You can pass t_span
into the function directly. The real time will be used for u
, or f
, if you will. Then define an index
for the for
loop; this index
will be used for y
.
function y = NARMA_optimized(u,mu,delta,phi,psi,m,t_span,k)
y = zeros(length(t_span),1);
% y(0)=0, and also y(-1)=0 etc.
%t = 1;
t = t_span(1);
index = 1;
y(index) = mu.* u(t-m-k).* u(t-k) + delta;
for t = t_span(2:end)
index = index + 1;
v = 1;
for i = 1:m
if index-i > 0 % else we add 0
v = v + y(index-i);
end
end
v = phi.*y(index-1) + v.*psi.*y(index-1) + mu.*u(t-m-k).*u(t-k) + delta;
y(index) = v;
end
end
Change the following in the main code:
M = 1; % Upper simulation time limit [seconds]
T = NARMA_optimized(f,Mu,delta,phi,psi,m,t_span,k_shift);
plot(t_span,T);