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I have mathematical model with 7 equation . and its difficult to find endemic equilibrium point with analitical , i want to solve with numerical method

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can you help me to find the endemic equilibrium point , with all the parameter known
close all; clear all; clc;
Pg=0.0068;
Ps=0.012;
Pr=0.006;
pe=0.002;
beta1=0.00702;
beta2=0.00702;
beta3=0.00702;
d4=1.7143;
u=0.05;
a1=1.10;
a2=4.6205;
a4=4.6666;
a5=1.10;
c1=0.0002;
c2=0.032;
c4=0.032;
c5=0.0002;
d10=1.2*10^-7;
d11=4.2*10^-8;
d12=1.0*10^-7;
d20=0.2051;
d21=0.00431;
d22=19.4872;
d50=1.2*10^-7;
d51=4.2*10^-8;
d52=1.0*10^-7;
tau=0.1615;
mu=0.00371;
psi=0.01813;
delta=2.4*10^-4;
gamma=0.136;
alpha=2.0;
%t = linspace(0,0.1,100)';
%tspan = [0 1000];
X0 = [1.0 0.01 0.0 1.0 0.0 0.01 0.01];
t0 = 0;
tf = 1000;
options = [];
%options=odeset('Abstol', 1e-6, 'Reltol', 1e-6);
[t,y1]=ode45(@glioma1,[t0:0.1:tf],X0,options,Pg,Ps,pe, beta1, beta2,a1, a2, a4, a5, c1,c2,c4,c5,u,d10,d11,d12,d20,d21,d22,d50,d51,d52,d4,tau,mu, beta3,psi, delta, gamma,alpha, Pr);
function hdot = glioma1(t,x,Pg,Ps,pe, beta1, beta2,a1, a2, a4, a5, c1,c2,c4,c5,u,d10,d11,d12,d20,d21,d22,d50,d51,d52,d4,tau,mu, beta3,psi, delta, gamma,alpha, Pr);
% The time-dependent term is A * sin(w0 * t - theta)
%H = 1*sin(-1*t);
%G = x(1)
hdot=zeros(7,1);
%H= heaviside(x(5));
v=0.6;
Phi=3.3*10^-3;
H=0;
if x(6)>0 || x(7)>0
H = 1;
%else%if (x(5)<=0);
% H = 0;
end
hdot(1)=Pg*x(1)*(1-x(1))-beta1*x(1)*(x(2)+x(3))-(d10+d11*x(4)+d12*x(7))*(x(1)*x(6))/(a1+x(1));
hdot(2)=Ps*x(2)*(1-(x(2)+x(3))/1+tau*x(4))-beta2*x(1)*x(2)-u*x(2)*H-(d20+d21*x(4)+d22*x(7))*(x(2)*x(6))/(a2+x(2));
hdot(3)=Pr*x(3)*(1-(x(2)+x(3))/(1+tau*x(4)))-beta3*x(1)*x(3)+u*x(2)*H-v*H*x(3);
hdot(4)=mu*(x(2)+x(3))+pe*x(4)*(1-x(4))-d4*((x(4)*x(7))/a4+x(4));
if (hdot(1)<0)
hdot(5)=alpha*hdot(1)*x(5)-(d50+d51*x(4)+d52*x(7))*(x(5)*x(6))/a5+x(5);
elseif (hdot(1)>0)
hdot(5)=-(d50+d51*x(4)+d52*x(7))*(x(5)*x(6))/a5+x(5);
end
hdot(6)=Phi-(psi+c1*x(1)/(a1+x(1))+c2*x(2)/(a2+x(2))+c5*x(5)/(a5+x(5)))*x(6);
hdot(7)=delta-(gamma+c4*x(4)/(a4+x(4)))*x(7);
%hdot = hdot';
%hdot=[hdot(:);H,h1];
% To make xdot a column
% End of FUN1.M
end
  1 Comment
Walter Roberson
Walter Roberson on 12 Apr 2023
The mathematics of ode45 is not valid when you have discontinuities in the first or second deriviatives of the equations. You need to construct event functions to detect each condition under which you are changing your equations -- detect x(6) or x(7) changing between negative and positive, detect hdot(1) changing between negative and positive.
Question: what should your hdot(5) be if hdot(1) is exactly 0?

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