How can I switch the differential equation according to the solution in ODE function ?

Hi. My differential equations are so complicated. So, I will try to simply explain my problem..

I am trying to solve differential equation using ODE45. For example,

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x0 = zeros(~~)

[t x] = ode45(@myfunction, tspan1, x0, options);

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and.. in the function

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function [DxDt] = myfunction(t,x)

DxDt = zeros(6,1)

a = matrix... and has to be switched according to (x) and (DxDt)

b = matrix... and has to be switched according to (x) and (DxDt)

DxDt = a*x + b

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It is simple. But..

I need to switch the matrix a and b according to the solution of my differential equation. What I mean is that I should have two differential equation in the function, and the equations have to switched.

For example, I have 2 equations, E1 and E2 which are differential equation form.

if a > x+DxDt+10, I should use E1. however if a <= x+DxDt+10, I should use E2.

I can switch it now, but it is possible at initial time according to the initial value x0. I want to switch the E1 and E2 at every step time. I tried to use 'for' , 'if', and whatever I can, but I couldn't solve this problem.

I think this is because the values of x (solution of the differential equation) can not be obtained in the function. And the value of DxDt should not be returned to a and b in the function.

How can I switch the equations according to x and DxDt ? Thank you for reading.

[Star Strider]

I suggest that you explore odeset, (specifically the ODE Events Property) and Event Location and Advanced Event Location for details.