where is the fault the code is not running as it has two delays with four variables?

function sol = exam4
options = ddeset('Events',@exam4e);
sol = dde23(@exam4f,[1, 10],[5; 0.1; 1],[0, 40],options);
xe = sol.xe;
ye = sol.ye;
ie = sol.ie;
n1 = find(ie == 1);
x1 = xe(n1);
y1 = ye(1,n1);
n2 = find(ie == 2);
x2 = xe(n2);
y2 = ye(2,n2);
n3 = find(ie == 3);
x3 = xe(n3);
y3 = ye(3,n3);
figure
plot(sol.x,sol.y,'k',x1,y1,'rs',x2,y2,'rs',x3,y3,'rs')
title('Infectious disease model from Hairer et alia.')
xlabel('Maxima are indicated by red squares.')
function yp = exam4f(x,y,Z)
ylag1 = Z(:,1);
ylag2 = Z(:,2);
k1 = 2;
k_1 = 1;
k2 = 1;
k3 = 1;
k_3 = 1;
k4 = 2;
k5 = 1;
k6 =1.5;
E1 = 1;
E2 = 2;
yp = [-k1*y(1)*E1+k_1*y(2)+k4*y(3);
    k1*y(1)*E1-(k_1+k2)*y(2)-k5*ylag1(1);
    k3*y(4)*E2-(k_3+k4)*y(3)-k6*ylag2(2);
    k2*y(2)+k_3*y(3)-k3*y(4)*E2+k5*ylag1(1)+k6*ylag2(2)];
function [value,isterminal,direction] = exam4e(x,y,Z)
value = exam4f(x,y,Z,);
isterminal = zeros(3,1);
direction = -ones(3,1);

[Steven Lord]

What does "not running" mean in this context?

• Do you receive warning and/or error messages? If so the full and exact text of those messages (all the text displayed in orange and/or red in the Command Window) may be useful in determining what's going on and how to avoid the warning and/or error.
• Does it do something different than what you expected? If so, what did it do and what did you expect it to do?
• Did MATLAB crash? If so please send the crash log file (with a description of what you were running or doing in MATLAB when the crash occured) to Technical Support so we can investigate.

[Torsten]

You define the initial value vector as (3x1) ([5; 0.1; 1]), but you try to solve for 4 unknowns (y(1)-y(4)).

This will give an error.

[Akhtar Jan]

[Akhtar Jan]

can you please correct this?

[Torsten]

Yes, as I said: Instead of a (3x1) vector ([5; 0.1; 1]) you must prescribe a 4x1 vector.

[Akhtar Jan]

[Akhtar Jan]

I replaced but couldnt run

[Torsten]

In exam4e, you also work with (3x1)...

Answer 1

[Torsten]

sol = exam4()

sol = struct with fields:
     solver: 'dde23'
    history: [4×1 double]
    discont: [0 1 2 3 10 11 12 20 21 30]
          x: [0 0.0017 0.0100 0.0404 0.0799 0.1286 0.1870 0.2568 0.3408 0.4446 0.5812 0.7631 1 1.0705 1.1411 1.2412 1.3637 1.5238 1.7619 2 2.3612 2.6806 3 3.5036 4.1851 4.7974 5.4500 6.0327 6.5176 7.0104 7.5991 8.3186 9.1593 10 10.1250 10.2500 … ]
          y: [4×93 double]
         xe: [0.8619 2.1568 2.8145 3.9275 4.0992 4.4285 4.8781 5.0578 5.6089 5.6448 6.2286 6.2739 6.7236 6.9830 7.4267 7.4846 8.3411 8.3953 9.2627 9.2852 10.0491 11.1232 12.9423 13.3956 14.3223 15.1159 15.4958 15.6244 16.0784 16.1023 16.6493 16.6748 … ]
         ye: [4×95 double]
         ie: [3 1 2 3 4 1 3 2 1 4 3 2 1 4 3 2 4 1 2 3 1 3 4 3 1 2 1 4 2 3 1 4 3 2 1 4 3 2 1 4 3 2 4 1 3 2 1 3 1 4 2 3 1 4 3 2 1 4 3 2 1 4 3 2 1 4 2 3 1 3 2 4 2 3 4 1 3 2 1 3 2 1 4 2 3 1 4 3 2 1 4 3 2 1 4]
      stats: [1×1 struct]
         yp: [4×93 double]

function sol = exam4
options = ddeset('Events',@exam4e);
sol = dde23(@exam4f,[1, 10],[5; 0.1; 1; 7],[0, 40],options);
xe = sol.xe;
ye = sol.ye;
ie = sol.ie;
n1 = find(ie == 1);
x1 = xe(n1);
y1 = ye(1,n1);
n2 = find(ie == 2);
x2 = xe(n2);
y2 = ye(2,n2);
n3 = find(ie == 3);
x3 = xe(n3);
y3 = ye(3,n3);
figure
plot(sol.x,sol.y,'k',x1,y1,'rs',x2,y2,'rs',x3,y3,'rs')
title('Infectious disease model from Hairer et alia.')
xlabel('Maxima are indicated by red squares.')
end
function yp = exam4f(x,y,Z)
ylag1 = Z(:,1);
ylag2 = Z(:,2);
k1 = 2;
k_1 = 1;
k2 = 1;
k3 = 1;
k_3 = 1;
k4 = 2;
k5 = 1;
k6 =1.5;
E1 = 1;
E2 = 2;
yp = [-k1*y(1)*E1+k_1*y(2)+k4*y(3);
    k1*y(1)*E1-(k_1+k2)*y(2)-k5*ylag1(1);
    k3*y(4)*E2-(k_3+k4)*y(3)-k6*ylag2(2);
    k2*y(2)+k_3*y(3)-k3*y(4)*E2+k5*ylag1(1)+k6*ylag2(2)];
end
function [value,isterminal,direction] = exam4e(x,y,Z)
value = exam4f(x,y,Z);
isterminal = zeros(4,1);
direction = -ones(4,1);
end

[Akhtar Jan]

Thanks