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I tried to convert odes to ss but i have problem//o​deToVector​Field

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syms x(t) f(t) x3(t) g(t) t
eqn1 = v == diff(x, t);
eqn2 = diff(v) == -3647.333890*x-99.48571587*v+3947.845868*x3+3947.845868*g+0.0002385211688*f;
eqn3 = diff(x3) == -0.004499581734*eqn2-0.71466948*v-28.3599*x+28.3599*g;
eqns = [eqn1 eqn2 eqn3];
V = odeToVectorField(eqns)
I want to solve this but it shows me error
i have 3 odes f and g are inputs x,v are outputs and x3 is state variable ?

  2 Comments

Star Strider
Star Strider on 12 Jan 2021
You will probably end up using equationsToMatrix, however you will have to edit your system first to make it compatible (and linear).

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Accepted Answer

Walter Roberson
Walter Roberson on 12 Jan 2021
Your code had some problems.
You were not declaring v as a function.
Your definition of eqn3 involved multiplying eqn2 by a value, but eqn2 is an equality and multiplying it by a value as part of an expression is dubious.
I had to guess what you might possibly mean by multiplying by eqn2 there. I probably guessed wrong, so review your system.
syms x(t) f(t) x3(t) g(t) v(t)
eqn1 = v == diff(x, t);
eqn2 = diff(v) == -3647.333890*x-99.48571587*v+3947.845868*x3+3947.845868*g+0.0002385211688*f;
eqn3 = diff(x3) == -0.004499581734*rhs(eqn2)-0.71466948*v-28.3599*x+28.3599*g;
eqns = [eqn1; eqn2; eqn3]
eqns(t) = 
vars = [f(t), g(t), v(t), x(t), x3(t)]
vars = 
[V, S] = odeToVectorField(eqns)
V = 
S = 

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