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Point out the error from this code

3 次查看（过去 30 天）
Syed Muhammad Umar
Syed Muhammad Umar 2015-10-12
关闭： MATLAB Answer Bot 2021-8-20
kindly Point out the error from this code as I am getting this message "Subscript indices must either be real positive integers or logicals"
% Initialize Variables
startTime = -20-9;
endTime = 40-9;
n = startTime:endTime;
x = zeros(size(n));
% Define x
x(abs(n) == 5 ) = 1.5;
x(abs(n) == 4 ) = 3;
x(abs(n) == 3 ) = 1;
x(abs(n) == 2 ) = 0;
x(abs(n) == 1) = -0.5;
x(n == 0) = 2;
y = zeros(size(n));
for i = 1:length(n)
if i > 1 % for i=1 cannot look back in time , i.e. there is no x(0)
y(i) = 5*x(i) + 5/3.* x(i-2) -2*x(i-5)+1/2.*x(i+2)+1/2.*y(i-2)-1/4.*y(i-4);
else
y(i) = 5*x(i);
end
end % Compute y[n] here. Be sure to account for edge conditions. (See
% MATLAB Tutorial 2 Lecture code for an example)
disp([num2str(toc*1000) ' ms' ]); % display run time in ms on cmd line
figure;
subplot(2,1,1);
stem(n,x, 'k' );
ylim([0 1.5]);
xlabel('n' , 'fontsize' ,13)
ylabel('amplitude' , 'fontsize' ,12)
title('x[n]' , 'fontsize' ,13)
subplot(2,1,2);
stem(n,y, 'r' );
ylim([0 1.5]);
xlabel('n' , 'fontsize' ,13)
ylabel('amplitude' , 'fontsize' ,12)
title('y[n]' , 'fontsize' ,13)
  1 个评论
Guillaume
Guillaume 2015-10-12
debug by forum is probably the least efficient way of debugging your code. You're better off using the tools provided by matlab.
In any case, the error message will also include a line number and the actual code that triggered the error. Please post this, rather than letting us guess.

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回答（2 个）

Thorsten
Thorsten 2015-10-12
编辑：Thorsten 2015-10-12
Your i runs from 1 to length(n), and you try to address x(i-5), x(i-2), i.e, x(-4), x(-1) for i=1. That's wrong, indices have to be positive in Matlab.
the cyclist
the cyclist 2015-10-12
编辑：the cyclist 2015-10-12
In this line
y(i) = 5*x(i) + 5/3.* x(i-2) -2*x(i-5)+1/2.*x(i+2)+1/2.*y(i-2)-1/4.*y(i-4);
you look back up to 5 time periods, so you are trying to access
y(-3)
when i = 2. That element obviously does not exist.

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