# Is there a block in Simulink to load equations in state variables ?

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Roberto Carabajal 2021년 9월 7일
댓글: Paul 2021년 9월 10일
I remember having seen some time ago a custom block in Simulink, that allowed to place a system of equations written in the format of state variables (in several lines). I haven't found it again and I don't see it in the repositories. I would be very grateful if someone could tell me about it.
My best regards.

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### 답변(3개)

Paul 2021년 9월 7일
This one?
##### 댓글 수: 1표시숨기기 없음
Paul 2021년 9월 10일
One can enter user defined differential equations in a Matlab Function block. The body of the function would look like:
function xdot = pendulum(x)
g = -9.81;
L = 1;
xdot(1) = x(2);
xdot(2) = -g/L*sin(x(1));
end
Mabe this is what you're looking for?
In any case, if you respond to this comment, please don't start a new answer. Instead, just type your response in the area underneath this comment that says in light gray "Comment on this answer ..."

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Roberto Carabajal 2021년 9월 8일
No, it was something like
x(1)= .........
x(2)= .......
x(3)= ........
where x(n) means derivative of x(n-1)
x(1) means x dot.
Each x() is placed in one line in the box
##### 댓글 수: 1표시숨기기 없음
Paul 2021년 9월 9일
Now I'm confused about what the equations are that need to be implemented. Can you write a few lines of Matlab code that illustrates an example set of equations?

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Roberto Carabajal 2021년 9월 9일
Suppose the sinple pendulum differential equation:
ẋ1=x2
ẋ2= -g/l*sin(x1)

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R2013b

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