Array indices must be positive integers or logical values.

%RK4 för I och U
% dI/dt = (U(I0.^2 + I.^2))/(L0*I0.^2)
% dU/dt = (-I)/C
 
% Konstanter
 
L0 = 0.7;     % [H]
I0 = 1;       % [A]
C  = 0.5e-6;  % [F]
 
% definera funktion 
 
fI = @(t,I,U) (U(I0^2+I^2))/(L0*I0^2);
 
fU = @(t,I,U) (-I)/C;
 
%initiella villkor
 
t(1) = 0;
I(1) = 0;
U(1) = 220;
 
%step size 
h = 0.001;
tslut = 0.01;
N = ceil(tslut/h);
 
% uppdate loop
 
for i = 1:N
    %update time
    t(i+1) = t(i) + h;
    %update U & I
    k1I = fI(t(i)    , I(i),         U(i));
    k1U = fU(t(i)    , I(i),         U(i));
    k2I = fI(t(i)+h/2, I(i)+h/2*k1I, U(i)+h/2*k1U);
    k2U = fU(t(i)+h/2, I(i)+h/2*k1I, U(i)+h/2*k1U);
    k3I = fI(t(i)+h/2, I(i)+h/2*k2I, U(i)+h/2*k2U);
    k3U = fU(t(i)+h/2, I(i)+h/2*k2I, U(i)+h/2*k2U);
    k4I = fI(t(i)+h  , I(i)+h  *k3I, U(i)+h  *k3U);
    k4U = fU(t(i)+h  , I(i)+h  *k3I, U(i)+h  *k3U);
    
    I(i+1)=I(i)+h/6*(k1I + 2*k2I + 2*k3I + k4I);
    U(i+1)=U(i)+h/6*(k1U + 2*k2U + 2*k3U + k4U);
    
end
 
%plot the 
 
plot(t,I)
hold on
plot(t,U)
xlabel('tid')
ylabel('ngt')
legend('I','U')
set(gca, 'fontsize', 16)


Array indices must be positive integers or logical
values.
Error in test2 (line 36)
    k2I = fI(t(i)+h/2, I(i)+h/2*k1I, U(i)+h/2*k1U);

why do I have the error in line 36?

Answer 1

[Image Analyst]

This is a FAQ, so see the FAQ

Answer 2

[madhan ravi]

See the attached file which works.

[Abdulraheem Kapara]

Thank you very much!

Also thanks for the comments!