ode45 MATLAB ODE solver

Hello I am using the MATLAB ODE solver ode45. But, the integration was not completed, and I still want to continue. So, How can I force the ode45 solver to continue???

[madhan ravi]

Upload the code so that it could be debugged.

[Ahmad Alalyani]

Here is the code I want to run.

function [g] = T(r)

global r

t0=1;

tfinal=5;

tspan=[t0 tfinal];

y0=[0;0;0;0];

while t0 < tfinal

[t,y]=ode45('F1',tspan,y0);

t0 = t(fix(length(t)/2));

%reset tspan for the next call to ode45 to integrate F2

tspan = [t0 tfinal];

[t,y]=ode45('F2',tspan,y0);

t0 = t(fix(length(t)/2));

%reset tspan for the next call to ode45 to integrate F1

tspan=[t0 tfinal];

%end of while loop

end

g = ...

********************************************************

The question is how to force ode45 to complete the integration across [1,5] before I pick t0 as, t0 = t(fix(length(t)/2)), and reset tspan to move to the next call to ode45?

[Walter Roberson]

Why are you continuing on from half way through the timespan it integrated over? Why not from the last time it integrated for?

Why are you passing in r and also declaring r to be global? MATLAB releases are changing with regards to what will happen for that situation. In some releases, the result would be to replace the passed in parameter 'r' with the current value of the global variable, which would probably be [] .

Answer 1

[Walter Roberson]

maxtries = 500;

first_time = 0;   %or as appropriate
end_time = 10;    %or as appropriate
tspan = [first_time, end_time];

y0 = [-1 3];  %set as appropriate
for counter = 1 : maxtries
  [this_t, this_y] = ode45(fun, tspan, y0);
  if counter == 1
    t{counter} = this_t; y{counter} = this_y;
  else
    t{counter} = this_t(2:end); y{counter} = this_y(2:end,:);
  end
  ended_at = this_t(end);
  if ended_at >= tspan(end)
    break;  %got to end of time span we wanted
  end
  tspan = [ended_at, end_time];
  x0 = this_y(end,:);
end

overall_t = cell2mat(t);
overall_y = cell2mat(y);

[madhan ravi]

Your brilliance is extraordinary Sir Walter I admire your work.

[Ahmad Alalyani]

Dear Sir Walter

Here is the code I want to run.

function [g] = T(r)

global r

t0=1;

tfinal=5;

tspan=[t0 tfinal];

y0=[0;0;0;0];

while t0 < tfinal

[t,y]=ode45('F1',tspan,y0);

t0 = t(fix(length(t)/2));

%reset tspan for the next call to ode45 to integrate F2

tspan = [t0 tfinal];

[t,y]=ode45('F2',tspan,y0);

t0 = t(fix(length(t)/2));

%reset tspan for the next call to ode45 to integrate F1

tspan=[t0 tfinal];

%end of while loop

end

g = ...

**********************************************************

The question is how to force ode45 to complete the integration across [1,5] before I pick t0 as, t0 = t(fix(length(t)/2)), and reset tspan to move to the next call to ode45?