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

Question

et77794 2018-2-19

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https://ww2.mathworks.cn/matlabcentral/answers/383548-line-11-error-subscript-indices-must-either-be-real-positive-integers-or-logicals

关闭： MATLAB Answer Bot 2021-8-20

euler.PNG

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!

 data = webread("https://web.njit.edu/~goodman/Math222/matlab1A.html")
 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);

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Bob Thompson 2018-2-19

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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.

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