how to update value of a function at each time step

Question

Olimpia 2014-8-22

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https://ww2.mathworks.cn/matlabcentral/answers/151969-how-to-update-value-of-a-function-at-each-time-step

评论： Olimpia 2014-8-22

Hi everyone, I am really stuck in creating a code that updates the value of my function K(t) at each time step and plots it. Seems quite simple but cant get my head around it.

at t=0 K(old)=3

at t=1 K(new_1)=K(old)+dt*dK/dt

at t=2 K(new_2)=K(new_1)+ dt*dK/dt

where dK/dt=4*exp(-30*(t - 3).^2)

for each subsequent time step we update the previous value with dK/dt

I would like to plot K(new) for t=0:0.01:10

Thanks!!

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Answer 1

Joseph Cheng 2014-8-22

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https://ww2.mathworks.cn/matlabcentral/answers/151969-how-to-update-value-of-a-function-at-each-time-step#answer_149538

编辑：Joseph Cheng 2014-8-22

在 MATLAB Online 中打开

So we start off with something like this

 dt = 0.01;
 t=0:dt:10;
 K = zeros(size(t)); %initialize it
 K(1) = 3;%setup initial value 
 for ind=2:length(t)
     K(ind) = K(ind-1)+dt*dK/dt; where t in your dKdt is subbed by t(ind);
 end
 figure,plot(t,K);

So what is performed above is that in the for loop i start at index of 2 to however long your t variable is. such that the t needed for your t=2 is the t(2) built by the t=0:dt:10; then as you can see from the equation i am looking at the current index and that is equal to the previous value + the defined 0.01 value for dt and the dK/dt.