MATLAB: Symbolic solutions to sysems of ODEs

MATLABodesymolic

I cannot get this to work, so please help:

syms r1 r2 r3 r4 L1 C1 ia(t) va(t) ic(t) vc(t) ic1 ic2

eqn3=va==L1*diff(ia,t);

eqn4=ic==C1*diff(vc,t);

eqn1=r1*ia+va+r2*(ia-ic)==0;

eqn2=r2*(ic-ia)+vc+r3*ic==0;

eqn=[eqn1;eqn2;eqn3;eqn4];

%calculate the ic's

ic1=4/(r4+(r1*r2/(r1+r2)))*r1/(r1+r2);

ic2=ic1*r2;

cond=[ic1;ic2];

dsolve(eqn,cond)

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hope that works:

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MATLAB: Solving equations using Laplace transform

Unless you are solving a partial differential equation, such that the Laplace transform produces an ordinary differential equation in one of the two variables and a Laplace transform of ‘t’, dsolve is not appropriate. It is simply necessary to solve for (in this instance) ‘Y(s)’ and then invert it to get ‘y(t)’:

syms t y(t) Y(s) Dy0 
 
Dy2 = diff(y,t,2); 
Dy1 = diff(y,t,1); 
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eqn = subs(eqn, {laplace(y(t), t, s), subs(diff(y(t), t), t, 0)},{Y(s), Dy0})
cond = [y(0)==4, Dy1(0)==5]; 
Soln_s = isolate(eqn, Y(s))
Soln_t = ilaplace(Soln_s)
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MATLAB: Attribute to an array of symbolic variables an array with their values

 V = num2cell([8 2 4 12 -6 0]);
 [R1 R2 R3 VA VB VG] = deal(V{:});

This does not have anything to do with the symbolic toolbox ? Or are you wanting to subs() like that? If so then

subs(TheExpression, [R1 R2 R3 VA VB VG], [8 2 4 12 -6 0])

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Related Solutions

MATLAB: Solving equations using Laplace transform

MATLAB: Attribute to an array of symbolic variables an array with their values

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