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# Line 11 Error: Subscript indices must either be real positive integers or logicals.

2 views (last 30 days)
et77794 on 19 Feb 2018
Closed: MATLAB Answer Bot on 20 Aug 2021
Hello! I am trying to code the attached image, but my code gets the error described in the question title. This is my code so far. Any help would be appreciated. Thank you!
tFinal = 2;
N = 33;
h=tFinal/N;
t=linspace(0,tFinal,N+1); % type 'help linspace' to see how this works
y=zeros(1,N+1);
yExact=9./(3*t-1+10*exp(-3*t));
y(1) = 1; % setting the initial condition
for n=1:N
k1 = y(n)*(3-t(n)*y(n));
k2 = y(n+h*k1)*(3-t(n+1)*y(n+h*k1));
y(n+1) = y(n) + h/2 * (k1+k2);
end
plot(t,y,t,yExact,'--')
xlabel('t'); ylabel('y'); title('Look, ma! I solved another ODE in MATLAB!');
error200= abs(y(N+1)-yExact(N+1));
fprintf('The new error is %f.\n', error200);
Bob Thompson on 19 Feb 2018
Assuming line 11 is:
k2 = y(n+h*k1)*(3-t(n+1)*y(n+h*k1));
Double check that your indices are turning up actual values, specifically k1, and if they are, then your issue may be in using * instead of .*, so it is trying to perform matrix multiplication rather than scalar multiplication.

Roger Stafford on 19 Feb 2018
In the line
k2 = y(n+h*k1)*(3-t(n+1)*y(n+h*k1));
the quantity n+h*k1 may not be a positive integer. If so, it is invalid as an index.

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