Error solving a neutral DDE

Hello,

I am trying to solve a set of neutral DDEs, using the code below

clc;clear;

S=.0725 ;  vL =1.0e-3; c = 1481; pvtinf=0 ; 
pinf0=1.01e5; k =7/5; rhoL=998;

d=10e-6;
R0=1e-6;
f=1e6;
ps=1e3;
X=[0 d];

tau1=[d/c,d/c,d/c,d/c];
tau2=[d/c,d/c,d/c,d/c];
y0=[R0,0,R0,0];


ff=@(t,x,xdel,xpdel)[x(2);
(((-0.5*x(2)^2)*(3-x(2)/(c))+(1+(1-3*k)*x(2)/c)*((pinf0-pvtinf)/rhoL+2*S/(rhoL*R0))*(R0/x(1))^(3*k)-2*S/(rhoL*x(1))-4*vL*x(2)/(rhoL*x(1))-(1+x(2)/c)*(pinf0-pvtinf+ps*subplus(sin(2*pi*f*t-2*pi*f*X(1)/c))/rhoL)-ps*x(1)*subplus(cos(2*pi*f*t-2*pi*f*X(1)/c)*2*pi*f/(rhoL*c)))-(2*xdel(3)*xdel(4)^2-xdel(3)*xpdel(4)^2)/d)/((1-x(2)/c)*x(1)+4*vL/(rhoL*c));
x(4);
(((-0.5*x(4)^2)*(3-x(4)/(c))+(1+(1-3*k)*x(4)/c)*((pinf0-pvtinf)/rhoL+2*S/(rhoL*R0))*(R0/x(3))^(3*k)-2*S/(rhoL*x(1))-4*vL*x(4)/(rhoL*x(3))-(1+x(4)/c)*(pinf0-pvtinf+ps*sin(2*pi*f*t-2*pi*f*X(2)/c))/rhoL-ps*x(3)*cos(2*pi*f*t-2*pi*f*X(4)/c)*2*pi*f/(rhoL*c))-(2*xdel(1)*xdel(2)^2-xdel(1)*xpdel(2)^2)/d)/((1-x(4)/c)*x(3)+4*vL/(rhoL*c));];


tspan =[0:0.01/f:20/f];
sol = ddensd(ff,tau1,tau2,y0,tspan);

Error using ddensd (line 236)
Index exceeds the number of array elements. Index must not exceed 2.

But it results in the following error which I am not sure where it is referring to. Any help is appreciated.

Answer 1

[Walter Roberson]

Last line of your dde, you have

(((-0.5*x(4)^2)*(3-x(4)/(c))+(1+(1-3*k)*x(4)/c)*((pinf0-pvtinf)/rhoL+2*S/(rhoL*R0))*(R0/x(3))^(3*k)-2*S/(rhoL*x(1))-4*vL*x(4)/(rhoL*x(3))-(1+x(4)/c)*(pinf0-pvtinf+ps*sin(2*pi*f*t-2*pi*f*X(2)/c))/rhoL-ps*x(3)*cos(2*pi*f*t-2*pi*f*X(4)/c)*2*pi*f/(rhoL*c))-(2*xdel(1)*xdel(2)^2-xdel(1)*xpdel(2)^2)/d)/((1-x(4)/c)*x(3)+4*vL/(rhoL*c));];
%                                                                                                                                                                                                                                   ^^^^

At the location I marked, you have X(4) but X is only 1 x 2 .

I would recommend that you rename one of X or x to avoid this confusion.

[Hossein]

Oh thank you that fixed the issue!