What is wrong with this code.
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% disp('%% -- Aufgabe 2.2.3 -- %%');
% Gitter erzeugen
[x y]=meshgrid([-2:0.05:2],0);
% Differentialgleichung
dx=x-x.^3;
ylim_extra=[-1/3 -1/3];
% Stabilitätsanalyse, Fixpunkte und zeitlicher Verlauf
[substatusflag,handle]=stabilitaetsanalyse(x,y,dx,zeros(size(y)),[],[],5,ylim_extra);
for i_count=2:4
set(handle(i_count),'XTick',[-2:2])
end
skizze_zeitverlauf(x,dx,5);
hold on % Analytische Lösung
t=0:0.05:2;
for startval=-2:0.25:2
C=(startval)/sqrt(1-startval^2);
plot(0,startval,'o','MarkerFaceColor',[0.75 0 0], ...
'MarkerEdgeColor',[0.75 0 0])
plot(t,exp(t)*C./sqrt(1+exp(2*t)*C^2), ...
'LineWidth',2,'Color',[0.75 0 0])
end
5 个评论
Dyuman Joshi
2023-9-11
It seems you have copied the code from somewhere and you don't have the user-defined functions "stabilitaetsanalyse" and "skizze_zeitverlauf".
You should ask the author of the code for these functions. We can not help you with this.
Walter Roberson
2023-9-11
https://www.researchgate.net/profile/Mohamed-B-Debbat/post/Strogatz_book_exercise_solutions/attachment/5c40a5733843b00675511560/AS%3A716089843531776%401547740531243/download/solution_manual_of_non_linear_dynamics.pdf related I suspect
ZAINULABADIN ZAFAR
2023-9-11
Dyuman Joshi
2023-9-11
"Is it possible that you can provide the code in easy way...thanks in advance."
As I mentioned earlier - We can not help you with this. You should ask the author of the code for these functions.
Walter Roberson
2023-9-11
The author of that code appears to be Dominik Zobel who was at dominik.zobel@tu-harburg.de
They posted code at a server that no longer exists.
回答（1 个）
Update: Thanks to @Walter Roberson for finding the source (PDF). The MATLAB functions stabilitaetsanalyse() and skizze_zeitverlauf() are unavailable. However, I tried to duplicate the results on page 3, section 2.2.3.
syms x(t) C
eqn = diff(x,t) == x - x.^3;
cond = x(0) == C; % initial value
xSol = dsolve(eqn, cond);
xSol = simplify(xSol)
c = -2:0.25:2; % range of initial values
for j = 1:numel(c)
xt = subs(xSol, C, c(j));
if c(j) >= 0
fplot( xt, [0 2], 'r'), hold on
else
fplot(-xt, [0 2], 'r'), hold on
end
end
hold off, grid on
xlabel('t')
ylabel('x(t)')
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2023-9-11
2023-9-11
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