MATLAB: Output from while-loop at fixed values

incrementoutputwhile loop

I am running time-dependent simulations with variable time-step size dt in seconds. I have implemented a while-loop that updates the elapsed time t_elapsed as t_elapsed + dt and stops when t_elapsed > t_total where t_total is a predefined number in seconds. Now I want to output the solution (a vector) to a text file at every x seconds, i.e. every 3600 seconds. This problem throws me of my game a bit as dt is now variable. Any help is much appreciated.

Arjan

Best Answer

Either compute the number of timesteps corresponding to your dt and desired frequency if dt is constant and output every N timesteps:

N=Tout/dt;
if mod(iterNo,N)==0
  fprintf(fid,data)
end

or, alternatively, test the time variable modulo Tout is within dt. ismembertol might be of interest here for floating point comparisons.

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MATLAB: Save While-loop to vector

Change it to the following:

VelocityVector=[];
while Velocity2>=-20
Velocity2=hastighet(acceleration(0,m,g),t,v0,t0);
VelocityVector=[VelocityVector; Velocity2];
 Height2=hojd(acceleration(0,m,g),t,h0,v0,t0);
   t=t+dt;
end

Then all your data is saved in VelocityVector.

MATLAB: Solving ODEs with different sets of initial conditions

function main
  n_times = 1000;
  t_i = 1; t_f = 10; tspan = [t_i,t_f];
  y0 = randn(2, n_times);
  y0 = reshape(y0, 2*n_times, 1);
  [t, y] = ode45(@(t,y) harmosc(t,y,n_times), tspan, y0);
  y = reshape(y,size(y,1),2,n_times)
  plot(t,y(:,1,15),t,y(:,2,15))
end
function dy = harmosc(t,y,n_times)
    y = reshape(y,2,n_times);
    dy = zeros(size(y));
    dy(1,:)=y(2,:);
    dy(2,:)=-y(1,:);  
    dy = reshape(dy,2*n_times,1);
end

Best Answer

Related Solutions

MATLAB: Save While-loop to vector

MATLAB: Solving ODEs with different sets of initial conditions

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