Why my y value went so high, whereas I using small value?

I am plotting M1 with RK4 function. I am just using small value of constant but the y value went so high

%input for time
t(1)=0;
dt=0.1; %time interval
t=0:dt:100; %time span

%input empty array
T=zeros(length(t),1); %empty array for t
M1=zeros(length(t),1); %empty array for M1
M2=zeros(length(t),1); %empty array for M2
M3=zeros(length(t),1); %empty array for M3
O=zeros(length(t),1); %empty array for O
P=zeros(length(t),1); %empty array for P

for j = 1:length((t))
    T(j+1)=T(j)+dt;
    M1(j+1)= M1(j)+1./(1+exp(-T(j))); 
    
    k1M1= dt*fRK4M1(M2(j),M3(j),O(j),P(j),M1(j));
    k2M1= dt*fRK4M1(M2(j)+k1M2/2,M3(j)+k1M3/2,O(j)+k1O/2,P(j)+k1P/2,M1(j)+k1M1/2);
    k3M1= dt*fRK4M1(M2(j)+k2M2/2,M3(j)+k2M3/2,O(j)+k2O/2,P(j)+k2P/2,M1(j)+k2M1/2);
    k4M1= dt*fRK4M1(M2(j)+k3M2/2,M3(j)+k3M3/2,O(j)+k3O/2,P(j)+k3P/2,M1(j)+k3M1/2);
    M1(j+1) = M1(j)+(1/6*(k1M1+(2*k2M1)+(2*k3M1)+k4M1));
    end

Unrecognized function or variable 'fRK4M2'.

  
figure;
plot (T,M1,'r','Linewidth',3)
xlabel('time')
ylabel('M1')

This is my RK function for M1

function M1 =fRK4M1(M1,M2,M3,O,P)  

  delta=50;
  K1= 10^-4;
  Ko=0.1;
  n=3;
  Oa=10;
  Pa=100;
  mu_1=10^-3;
  mu_2=10^-3;
  mu_3=10^-3;
  mu_o=10^-4;
  mu_p= 10^-5;
  K2=5*10^-4;
  K3=10^-3;
  gamma=75;
     
     M1=(delta*M1*(1-(M1/gamma))-2*K1*M1*M1-M1*(K2.*M2)-((Oa-n)*K3*M1*M3)-((Pa-Oa)*Ko*M1*O)-(mu_1*M1)); 

And this is my plot

[Image Analyst]

People may wait to answer until you attach the fRK4M2 variable or function so that they can run your code.

[cindyawati cindyawati]

function M2 =fRK4M2(M2,M1)
M1=10;
M2=0;
mu_2=10^-3;
K1= 10^-4;
K2=5*10^-4;
K3=10^-3;


M2 = (K1*M1*M1)-(K2*M1*M2)-(mu_2*M2);

This is my FRK4M2 function

Answer 1

[Steven Lord]

Look at the way you're calling your function in the loop:

 k1M1= dt*fRK4M1(M2(j),M3(j),O(j),P(j),M1(j));

and the way you've defined it:

function M1 =fRK4M1(M1,M2,M3,O,P)

Did you mean for M1 to be the first input argument in the definition but the last in the call? That smells like a bug.

There's also nothing in your code that changes any element of M2, M3, O, or P from their initial values of 0 so you could save time by simply omitting them from the calls (replacing them with 0.)

[cindyawati cindyawati]

It is work for M1, thank you @Steven Lord

k1M1= dt*fRK4M1(M1(j),M2(j),M3(j),O(j),P(j));

Unrecognized function or variable 'dt'.

but i try to M2, M3, P, and O it is doesnt work

k1M2 = dt*fRK4M2(M1(j),M2(j));

function for M2

function M2 =fRK4M2(M1,M2)
M1=10;
M2=0;
mu_2=10^-3;
K1= 10^-4;
K2=5*10^-4;
K3=10^-3;


M2 = (K1*M1*M1)-(K2*M1*M2)-(mu_2*M2);
end

M2, M3, P, and O I want to get like sigmoid graph but I get linear plot for M2,M3,P, and O