ode23 calling and speicified time problems

hello,

i have a prog. below

*global Ua Ub

Ua=3; Ub=0;

[t,x]=ode23('train',[0,5],[0;0]);

subplot(3,1,1);plot(t,x(:,1));ylabel('displacement');xlabel('second'); grid on

subplot(3,1,2);plot(t,x(:,2)); ylabel('velocity');xlabel('second'); grid on*

now my question is that there is a train function in my program and olsa in this function i use Ua and Ub as a global variable. But Ua not a constant afer 5 second it is changing to 5 for example and i have to call ode23 to solve it again with a new value of Ua .

Now here some problems.

the first problem is initial value prblem because for example time between 0 and 5 second Ua=3 at t =5 there is a output x(:,1)=20 and when i change ua=5 i call it ode23 again like

[t,x]=ode23('train',[now here 5to10],[now i should write here fisrt ode23 solution x(:,1) last value as a initial value and x(:,2) too but i cannot find them without counting hw many value for ex last vluae x(31,1) ]

as a result , I CANNOT USE LAST VALUE OF RESULT OF FİRST ODE23 SOLUTION AND I CANNOT PLOT THE WHOLE VALUE WİTH PLOT(T,X(:,1)) COMMAND BECAUSE İT TAKES LAST VALUE OF ODER23 NOT T[0,5] ONLY T[5-10]

HOW CAN I HANDLE ??

THANKS FOR YOUR HELP