Why do I get "Array indices must be positive integers or logical values" when I am trying to plot my functions?

figure(1)

alpha=0.89;

beta=0.89;

gamma=0.5;

c(0)=1;

i(0)=1;

y(0)=2;

for t=1:50

y(t) = c(t) + i(t);

c(t) = alpha*y(t - 1);

i(t) = beta*(c(t) - c(t - 1)) + gamma;

end

plot(y,'LineWidth',2)

hold on

plot(c,'LineWidth',2)

plot(i,'LineWidth',2)

xlabel('Time period')

ylabel('BKT (M€)')

Hey! I am trying to plot this, but for some reason I get the message "Array indices must be positive integers or logical values". What seems to be the problem in my code?

Answer 1

[Mathieu NOE]

hello

1/ matlab is a language where indexing is 1 based and not zero based

2/ next correction is that y must be computed once c and i are updated in the for loop

so a working code is :

figure(1)
alpha=0.89;
beta=0.89;
gamma=0.5;
c(1)=1;
i(1)=1;
y(1)=2;
for t=2:50
    c(t) = alpha*y(t - 1);
    i(t) = beta*(c(t) - c(t - 1)) + gamma;
    y(t) = c(t) + i(t);
end
plot(y,'LineWidth',2)
hold on
plot(c,'LineWidth',2)
plot(i,'LineWidth',2)
xlabel('Time period')
ylabel('BKT (M€)')

[Jenni]

Excellent! Thank you for your help!

Answer 2

[Austin M. Weber]

In MATLAB, indexing starts at 1, so you cannot have C(0), i(0), or y(0). Rather, it needs to be C(1), i(1), or y(1).

EDIT: @Mathieu NOE is correct, in addition to what I said, that also means that you need to start your for-loop at index position 2 instead of position 1. Otherwise, when your script gets to this line:

for t = 1:50
    c(t) = alpha*y(t - 1);

You will still get an error because y(t-1) would be the same as y(0) in the first iteration of the loop. So, you have to start the loop at t = 2:50:

for t = 2:50

[Jenni]

Great, thank you!

Answer 3

[Image Analyst]

See the FAQ:

Subscript indices must either be real positive integers or logicals