Question on DDE23

I have been trying to solve a system of delay differential equations where the delay paramter is included in the 5th state variable that appears in the first two equations using DDE23. First, I coded the system as

function yp = ddefunc(~,y,Z)

yl1=Z(:,1);

yp = [a*y(1)-b*yl1(2); c*y(2) ];

end

Then, I solved the system using the dde23 solver as

a=0.05;

b=0.5;

c=0.5;

lags=1;

tspan=[0 10];

sol = dde23(@ddefunc,lags,[0.8; 0.2],tspan);

However, Matlab responed with this

Unrecognized function or variable 'a'.

I tried to use other codes available in the internet but I always ended up with the same error.

Please help!!

Answer 1

[Torsten]

lags=1; 
tspan=[0 10]; 
sol = dde23(@ddefunc,lags,[0.8; 0.2],tspan);
plot(sol.x,sol.y(1,:))

function yp = ddefunc(~,y,Z) 
  a=0.05; 
  b=0.5; 
  c=0.5; 
  yl1=Z(:,1); 
  yp = [a*y(1)-b*yl1(2); c*y(2) ]; 
end

[Fares]

Dear Torsten,

Thank you so much for your help. I really appreicate it!!

Answer 2

[Steven Lord]

Nowhere in your ddefunc function do you define the variables a,b, etc. The fact that you've defined them in the script or function from which you call dde23 does not by default make them available inside ddefunc.

Use one of the techniques shown on this documentation page to make those values available to ddefunc, or if they're only used inside ddefunc move the lines of code that define those parameters into ddefunc.