merging two ode graphs

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Susmita Panda
Susmita Panda on 6 May 2021
Commented: Susmita Panda on 16 May 2021
I tried to merge two ode function but getting an error. The first ode ranges upto T and thereafter I want result of other ode.

Accepted Answer

Alan Stevens
Alan Stevens on 8 May 2021
Your testode2 function must return a column vector. Try
function dy = testode2(~,y) %%% Must return a column vector
j=1;beta=0.025;k=j^4;c=2*j^2*beta;m=1;
f=zeros(2,1);
dy = [y(2);
(-k*y(1)/m-c*y(2)/m)];
end
  4 Comments
Alan Stevens
Alan Stevens on 11 May 2021
Perhaps you mean more like this:
wb=14.25;eta=0.15;T=pi/(wb*eta);
tspan_1=[0:0.001:T];
tspan_2=[T:0.001:10];
y0_1=[0;0];
%y0_2=[0.02 0.05];
[t1,y1]=ode45(@diffeqn11,tspan_1,y0_1);
[r,c]=size(y1);
y0_2 = y1(r,:);
[t2,y2]=ode45(@testode2,tspan_2,y0_2);
%plot
plot(t1, y1(:,1), 'r', 'LineWidth',2);
hold on
plot(t2, y2(:,1), 'b', 'LineWidth',2);
function dy = testode2(~,y)
j=1;beta=0.025;k=j^4;c=2*j^2*beta;m=1;
f=zeros(2,1);
dy = [y(2);
-k*y(1)/m-c*y(2)/m];
end
function f= diffeqn11(t,y)
eta=0.15;wb=14.25;j=1;beta=0.025;P=6;L=20;mb=3000*9.81/20;v=27.77;x=0.5;
%A=sin(j*pi*x/L);
f=zeros(2,1);
f(1)=y(2);
f(2)=j^2*sin(j*eta*t)-(j^4*y(1))-(2*beta*j^2*y(2));%dimensionless
%f(2)=(2/mb*L)*P*sin(j*pi*v*t/L)-2*beta*wb*y(2)-wb^2*y(1);%non-dimensioned Qb
end

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