Why is the hold on function causing 3 graphs?

clc%clears screen
clear all%clears history
close all%closes all files
format long
k=7.13*10^3;
alpha=0.001;
beta=0.0041;
f=@(t,x) k*(alpha-x).^2.*(beta-x/2);
prev=0;
h=10;





while(1)
    [t,x]=kutta(f,[0,10],0,h);
        if(abs(x(end)-prev)/abs(prev)<0.000001)
        break;
end
h=h/10;
prev=x(end);
end
disp('Approximate x(10) is');
disp(x(end));
disp('The value of h is')
disp(h)


plot(t,x,'b')

function [x,y]=kutta(f,tspan,y0,h)
x = tspan(1):h:tspan(2); % Calculates upto y(3)
y = zeros(length(x),1);
y(1,:) = y0; % initial condition
for i=1:(length(x)-1) % calculation loop
    k_1 = f(x(i),y(i,:));
    k_2 = f(x(i)+0.5*h,y(i,:)+0.5*h*k_1);
    k_3 = f((x(i)+0.5*h),(y(i,:)+0.5*h*k_2));
    k_4 = f((x(i)+h),(y(i,:)+k_3*h));
    y(i+1,:) = y(i,:) + (1/6)*(k_1+2*k_2+2*k_3+k_4)*h; % main equation
    
end
hold on
plot(x,y,'r')
legend('Exact','Kutta')

end

Whenever I run this 3 graphs appear. I do not want the straight line one and dont know where im mesing up at. Please help.

[KSSV]

Remove the plot inside the function. You are plotting inside the function also.

[Daniel Hein]

What do you mean? If i remove the plot function outside of the function the code wont run. unless im misunderstood what you meant.

Answer 1

[Mahesh Taparia]

Hi

Based on the parameters you have specified, the function kutta has been called for three times which resuls in 3 plots inside the function (2 with same curve) and one plot is because of last line of the main code. For better understanding apply break point in the loop and analyze the plot.