What is wrong with this code.

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ZAINULABADIN ZAFAR
ZAINULABADIN ZAFAR 2023-9-11
评论： Walter Roberson 2023-9-11
Ran in:
% 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);
Unrecognized function or variable 'stabilitaetsanalyse'.
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
显示 3更早的评论
Dyuman Joshi
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
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.

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回答（1 个）

Sam Chak
Sam Chak 2023-9-11
编辑：Sam Chak 2023-9-11
Ran in:
Hi @ZAINULABADIN ZAFAR
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)
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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