Runge-kutta (rk2) for radio decay

solve the equation

dN(t)/dt=-N(t)/tau

decay constant=1

initial nuclei=1000 @ t=0

my code so far is:

%radioactive decay

t0=0

N0=1000

tf=5

dt=.05

tau=1

%Initialize

t=t0:dt:tf;

N=zeros(size(t));

N(1)=N0;

t(1)=t0;

for i =2:length(t);

    tn=t(i-1);

    Nn=N(i-1);

    Y1=dt*decay(tn,Nn);

    Y2=dt*decay(tn+dt/2,Nn+Y1/2,tau);

    Y3=dt*decay(tn+dt/2,Nn+Y2/2,tau);

    Y4=dt*decay(tn+dt,Nn+Y3,tau);

    N(i)=Nn+((Y1+Y4)/2+(Y2+Y3))/3;

end;

plotcompare(t,N,N0,tau,'RK4')

it keeps running the error message 'too many input arguments'

Am i headed in the right direction? anything will help

thanks

[James Tursa]

Please show the decay code. Note that you are calling decay with only 2 arguments in the Y1 line, but with 3 arguments in the other lines.

Answer 1

[Michael Abboud]

When I tried to run your code, I received the following error message: “PDS is not a polytopic or parameter-dependent system”, so I’m wondering if you perhaps wrote your own “decay” function.

However, if you are using the MATLAB “decay” function from the Robust Control Toolbox, appears from the documentation page that “decay” has only two inputs: “ps” and “options”. Here, “options” is an array of 2 values, yet you are passing in 3 separate arguments.

Instead of using the line:

>> Y2 = dt * decay( tn+dt/2, Nn+Y1/2, tau);

Try the following:

>> options = [Nn+Y1/2 , tau];
>> Y2 = dt*decay( tn+dt/2, options);