How to plot this while loop?

Question

Desiree 2019-8-1

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/474447-how-to-plot-this-while-loop

评论： Star Strider 2019-8-1

Hello. I’m trying to plot this while loop with no success. Each time it gives me a blank plot. Tried using hold on at the end of the loop, before the loop, or just using plot but without results. The codes work perfectly fine without plotting as it displays all the results that I want. Here I wish to plot both sigma and u in one same plot (but even tried only sigma, still nothing). Here it is:

      t=0;
      x=[1,1,1];
      v=x(1);
      vc=sin(t+1)-cos(0.5*t-2);
      sigma=v-vc;
      alpha=30;
      tau=0.0001;
      while t<=10
          f=-sin(t+5)-0.5*cos(t)-x(2);
          v=x(1);
          vc=sin(t+1)-cos(0.5*t-2);
          vcc=cos(t+1)+0.5*sin(0.5*t-2);
          sigma=v-vc;
          sigmadot=f-vcc;
          u=alpha*((abs(sigmadot)).^2*sign(sigmadot)+sigma)/((sigmadot).^2+abs(sigma));
          dx=[f,cos(1+x(1)+x(3))+(2-cos(x(1)+x(3)+1))*u,cos(x(1)+0.5*x(3)-t)-x(3)+u];
              x=x+dx*tau;
              t=t+tau;
      end

Please if someone can tell me how to plot this properly or if maybe there is a way to rewrite the code without the while loop so I can plot it without a problem hopefully, It will be appreciated.

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Answer 1

Star Strider 2019-8-1

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/474447-how-to-plot-this-while-loop#answer_385777

在 MATLAB Online 中打开

Try this:

t=0;
x=[1,1,1];
v=x(1);
vc=sin(t+1)-cos(0.5*t-2);
sigma=v-vc;
alpha=30;
tau=0.0001;
k = 1;                                              % Counter
while t<=10
    f=-sin(t+5)-0.5*cos(t)-x(2);
    v=x(1);
    vc=sin(t+1)-cos(0.5*t-2);
    vcc=cos(t+1)+0.5*sin(0.5*t-2);
    sigma=v-vc;
    sigmadot=f-vcc;
    u=alpha*((abs(sigmadot)).^2*sign(sigmadot)+sigma)/((sigmadot).^2+abs(sigma));
    dx=[f,cos(1+x(1)+x(3))+(2-cos(x(1)+x(3)+1))*u,cos(x(1)+0.5*x(3)-t)-x(3)+u];
    x=x+dx*tau;
    t=t+tau;
    sigmav(k) = sigma;                              % Vector
    uv(k) = u;                                      % Vector
    tv(k) = t;                                      % Vector
    k = k + 1;                                      % Increment Countr
end
figure
plot(tv, uv)
grid
figure
plot(tv, sigmav)
grid