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can anyone help me ?

Asked by diadalina on 2 Jun 2019
Latest activity Edited by Stephan
on 2 Jun 2019
here is a code matlab of one degree differential equation, i want to plot the error method for different values of N, can anyone help me

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Geoff Hayes
on 2 Jun 2019
diadalina - please clarify what you mean by i want to plot the error method for different values of N. Does your code do some or all of this already? If not, where should this happen in your attached code?
diadalina on 2 Jun 2019
the error wich is equal to norm(the approchsolution-the exactsoltuion), i want to show the accuracy of the numerical method used here , my code doesn't work correctly !!

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1 Answer

Stephan
Answer by Stephan
on 2 Jun 2019
Edited by Stephan
on 2 Jun 2019

clear all;
clc;
close all;
N=[100,200,300,400];
hold on
for k=1:numel(N)
%%les données mathématiques
t = 0:1/(N(k)-1):1;
%les conditions initiales
c0=0;
%%résolution de notre système
[~,Y]=ode45(@systest,t,c0 );
sol_exacte=t.*exp(t);
subplot(2,1,1)
plot(t,Y(:,1),t,sol_exacte,'+')
legend('sol-app','sol-exacte')
err(k)=norm(Y(:,1)'-sol_exacte)
e=err(k);
end
hold off
subplot(2,1,2)
semilogy(N,err,'ob--')
legend('error')
function F=systest(t,Y)
F(1,1)=Y(1)+exp(t);
end

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