Error in solving ode using symbolic calculations

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Roman Gilgor 2020-3-1

关闭： MATLAB Answer Bot 2021-8-20

hi, I am trying to compare my solution using ode45 and runge kutta to analytical solution of symbolic matlab.

Iam solving a simple system of linear ode equations: (this is the code)

syms s1(t) s2(t) I(t) u(t)

u(t) = 10; % input

% system of odes

ode1 = diff(s1) == u(t) - s1/55; % equation 1

ode2 = diff(s2) == s1/55 - s2/55; % equation 2

ode3 = diff(I) == s2/(0.12*55*60) - 0.138*I; % equation 3

odes = [ode1; ode2; ode3];

%initial conditions

cond1 = s1(0) == 0;

cond2 = s2(0) == 0;

cond3 = I(0) == 0;

conds = [cond1; cond2; cond3];

[s1Sol(t), s2Sol(t),Isol(t)] = dsolve(odes,conds)

I would like to see what Isol(t) is equal to. Every time I change the numbers at equation 2 or 3 it changes the solution of only equation 1! why????

I solved this analyticly on papper and its definetly wrong.

both ode45 and runge kutta gives me the same answer but for some reason analytical matlab solution is wrong.

Please help.

Thanks allot!!!

by the way this is ode45 function

% initial conditions are 0 0 0

% time interval 0 - 10

function dydt = odefun(t,y)

dydt = zeros(3,1);

dydt(1) = 10 - y(1)/55;

dydt(2) = y(1)/55 - y(2)/55;

dydt(3) = y(2)/(55*0.12*B60) - 0.138*y(3);

end

darova 2020-3-1

What is this?

Roman Gilgor 2020-3-1

编辑：Roman Gilgor 2020-3-1

Hi, avoid this ita my mistake in copying it from matlab. It just 0.12*60 Thanks!

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