# How to store conditional values during iteration by using Ode45?

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Cola on 27 Aug 2021
Commented: Wan Ji on 27 Aug 2021
I want to store data of each iteration, including the conditional values. Is there a way to do this? Thanks!
There is an example where 'b' is the conditional value. And the goal ([b0,t,X1]) is as follows:
1 0 1.0000
1 1.0000 1.5378
1 2.0000 1.6115
1 3.0000 1.6175
1 4.0000 1.6180
1 5.0000 1.6180
2 0 1.0000
2 1.0000 1.9317
2 2.0000 1.9987
2 3.0000 2.0000
2 4.0000 2.0000
2 5.0000 2.0000
3 0 1.0000
3 1.0000 2.2584
3 2.0000 2.3036
3 3.0000 2.3028
3 4.0000 2.3028
3 5.0000 2.3028
Code：
save=[]
t0=0;
tf=15;
a0=1
global b0;
for b0=1:1:3
X=[a0]
[t, X1] = ode45(@fun,[t0:0.1:tf], X);
% X2=[b0,t,X1(1)];
X2=[t,X1];
save=[save;X2]
end
function fx=fun(t,x)
fx=zeros(1,1);
global b0
b=b0
fx(1)=x(1)-x(1)^2+b
end

Wan Ji on 27 Aug 2021
Edited: Wan Ji on 27 Aug 2021
You can define a table to store the data including the conditional values
function main
t0=0;
tf=15;
a0=1;
T = table();
global b0;
for b0=1:1:3
X=[a0];
[time, xval] = ode45(@fun,[t0:0.1:tf], X);
b = b0*ones(size(time));
T = [T; table(b, time, xval)]; % use table T to store the data
end
writetable(T,'Table.txt')
end
function fx=fun(t,x)
fx=zeros(1,1);
global b0
b=b0;
fx(1)=x(1)-x(1)^2+b;
end
The final file Table.txt is what you need
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Wan Ji on 27 Aug 2021
My pleasure