MATLAB: OdeToVectorField: Unable to convert the initial value problem to an equivalent dynamical system.

differential equationsdynamical systeminitial conditionsodetovectorfield

Could anyone help me with following Matlab codes. Why do they generate error and how to fix them?
syms t v1(t) v2(t) v3(t)
equ=[v1(t) == 10e-03*sin(2*pi*1e08*t);...
    1e-00*(v2(t)-v1(t))+1e-03*(v2(t)-v3(t))+1e-09*diff(v2(t)-v3(t),t) == 0;...
    1e-03*(v3(t)-v2(t))+1e-09*diff(v3(t)-v2(t),t)+1e-03*v3(t) == 0];
Vect=odeToVectorField(equ);

Best Answer

Hi,
i deleted my first answer - cause your comment brought me to a new thought - DAE:
syms t v1(t) v2(t) v3(t)
eq1 = v1(t) == 10e-03*sin(2*pi*1e08*t);
eq2 = 1e-00*(v2(t)-v1(t))+1e-03*(v2(t)-v3(t))+1e-09*diff(v2(t)-v3(t),t) == 0;
eq3 = 1e-03*(v3(t)-v2(t))+1e-09*diff(v3(t)-v2(t),t)+1e-03*v3(t) == 0;
eqs = [eq1 eq2 eq3];
vars = [v1 v2 v3];
f = daeFunction(eqs,vars)
This works and gives you a function handle which can be used with ode15i:
f =
  function_handle with value:
    @(t,in2,in3)[in2(1,:)-sin(t.*6.283185307179586e8)./1.0e2;in3(2,:)./1.0e9-in3(3,:)./1.0e9-in2(1,:)+in2(2,:).*1.001-in2(3,:)./1.0e3;in3(2,:).*(-1.0e-9)+in3(3,:)./1.0e9-in2(2,:)./1.0e3+in2(3,:)./5.0e2]
I'm sorry that I notice so late!
Best regards
Stephan
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