What is wrong with this code.

% 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

[Dyuman Joshi]

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]

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]

Yes, I have copied it from "Debbat/post/Strogatz_book_exercise_solutions/attachment/5c40a5733843b00675511560/AS%3A716089843531776%401547740531243/download/solution_manual_of_non_linear_dynamics.pdf".

As you have mentioned. Is it possible that you can provide the code in easy way...thanks in advance.

[Dyuman Joshi]

"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]

The author of that code appears to be Dominik Zobel who was at [e-mail]

They posted code at a server that no longer exists.

Answer 1

[Sam Chak]

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)')