Array indices must be positive integers or logical values error

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Juan Gadd 2020-2-25

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/507535-array-indices-must-be-positive-integers-or-logical-values-error

关闭： MATLAB Answer Bot 2021-8-20

I need to calculate the velocity, and height of a rocket for each iteration from acceleration. However the code will only run a_i, and u_i, and wont give out h_i claiming that the array indices must be positive integers or logical values. The code below is how I am trying to solve it.

for n=linspace(0,50,7500)

syms a_i u_1 h_i

g_i=g_0;

a_0=T_0/m_0-g_0*cosd(Theta_0)-(rho_0*(u_0^2)*Cd_On(1)*A)/(2*m_0);

u_i=zeros(1,7500);

h_i=zeros(1,7500);

a_i=[a_0 (T_t./m_t)-g_i.*cosd(Theta_0)-(rho_0.*(u_i(1-n).^2).*Cd_On*A)./(2.*m_t)];

u_i=u_i(1-n)+(a_i+a_i(1+n)).*(dt)/2;

h_i=h_i(1-n)+u_i(n).*(dt);

end

I have tried fixing it by modifying the code to the code below, but it can't even run a_i.

for i=linspace(0,50,7500)

g_i=g_0;

a_y_0=(T_0./m_0)-(g_0.*cosd(Theta_0))-(rho_0.*(u_0^2).*Cd_On(1)*A/(2.*m_0));

u_y_i=zeros(1,7500);

h_i=zeros(1,7500);

a_y_i=[a_y_0 (T_t./m_t)-g_i.*cosd(Theta_0)-(rho_0.*(u_y_i(i+dt).^2).*Cd_On*A)./(2.*m_t)];

u_i=u_i(1-n)+(a_i+a_i(1+n)).*(dt)/2;

h_i=h_i(1-n)+u_i(n).*(dt);

end

Thanks for the help.

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Answer 1

Image Analyst 2020-2-25

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/507535-array-indices-must-be-positive-integers-or-logical-values-error#answer_417330

编辑：Image Analyst 2020-2-25

在 MATLAB Online 中打开

See the FAQ: Subscript_indices_must_either_be_real_positive_integers_or_logicals?

Try this:

values = linspace(0,50,7500);
for k = 1 : length(values)
	n = values(k);
	%     syms a_i u_1 h_i
	g_i=g_0;
	a_0=T_0/m_0-g_0*cosd(Theta_0)-(rho_0*(u_0^2)*Cd_On(1)*A)/(2*m_0);
	u_i=zeros(1,7500);
	h_i=zeros(1,7500);
	a_i=[a_0 (T_t./m_t)-g_i.*cosd(Theta_0)-(rho_0.*(u_i(1-n).^2).*Cd_On*A)./(2.*m_t)];
	u_i=u_i(1-n)+(a_i+a_i(1+n)).*(dt)/2;
	h_i=h_i(1-n)+u_i(n).*(dt);
end