Discrepancy with easy ODE.

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Bobby Fischer
Bobby Fischer 2021-1-14
评论： Bobby Fischer 2021-1-14
Hello, don't know why the discrepancy.
function fcno
y0=linspace(0,2,20);
t0=linspace(0,3,100);
figure(1)
close(1)
figure(1)
options=odeset('RelTol',1e-5);
subplot(1,3,1)
hold on
for k=1:20
[t,y]=ode45(@fun,t0,y0(k),options);
plot(t,y,'b')
end
title('ode')
subplot(1,3,2)
hold on
t=t0;
for k=1:20
f2=y0(k)*exp(t)./(1+(exp(t)-1)*y0(k));
plot(t,f2,'r')
end
title('solution')
%%
lon=101;
t=linspace(0,3,lon);
h=3/(lon-1);
y0=linspace(0,2,20);
subplot(1,3,3)
hold on
for m=1:20
y=zeros(1,lon);
y(1)=y0(m);
for k=1:100
y(k+1)=y(k)+h*y(k)*(1-y(k));
end
plot(t,y,'g')
end
plot([0 3],[0 0],'m--','linewidth',3)
plot([0 3],[1 1],'m--','linewidth',3)
title('my ode')
%%
function [t,yp]=fun(t,y)
yp=y*(1-y);
end
end
  2 个评论
Mischa Kim
Mischa Kim 2021-1-14
Hi Bobby, can you please provide more information of what you are trying to accomplish and the (unexpected) results you receive?
Bobby Fischer
Bobby Fischer 2021-1-14
Thanks Mischa. All clear.

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采纳的回答

J. Alex Lee
J. Alex Lee 2021-1-14
You have a syntax error on what your odefun is returning. To fix:
function [yp]=fun(t,y)
yp=y*(1-y);
end

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