??? Subscript indices must either be real positive integers or logicals

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Brooke 2011-12-27

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https://ww2.mathworks.cn/matlabcentral/answers/24811-subscript-indices-must-either-be-real-positive-integers-or-logicals

I have a for loop that gives the values of x(n) -- here n is an index.

d=0.5;
 
x(1)=1;
 
for n=2:10
x(n)= x(n-1)+d;
y(n)= log(abs(x(n)));
fprintf('y(%d)=%d', n, y(n))
end

I want the loop to also give the values of y(n) = log(abs(x(n))).

However, MATLAB doesn't seem to like this definition and I am presented with the error message: ??? Subscript indices must either be real positive integers or logicals.

What should I do to fix it?

Thanks.

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Jan 2011-12-27

Please post the relevant part of the code instead of describing it.

Brooke 2011-12-27

@Jan: I have posted the code.

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采纳的回答

bym 2011-12-27

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matlab is ones based, not zeros... x(0) is an error

[edit]

works fine for me (added \n in fprintf statement)

d=0.5;
x(1)=1;
for n=2:10
x(n)= x(n-1)+d;
y(n)= log(abs(x(n)));
fprintf('y(%d)=%d\n', n, y(n))
end
y(2)=4.054651e-001
y(3)=6.931472e-001
y(4)=9.162907e-001
y(5)=1.098612e+000
y(6)=1.252763e+000
y(7)=1.386294e+000
y(8)=1.504077e+000
y(9)=1.609438e+000
y(10)=1.704748e+000

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bym 2011-12-27

do a clear; before running your script

Brooke 2011-12-27

@proecsm: Thanks, that worked!! :)

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更多回答（2 个）

Jan 2011-12-27

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在 MATLAB Online 中打开

Either n is not an integer greater than 0 or the symbols log or abs have been defined as variables, such that the built-in functions are shadowed. You can test this by using:

dbstop if error

and start the program. Then Matlab stops when the error occurs and you can check the symbols by:

which abs
which log

The command whos can be helpful also.

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Brooke 2011-12-27

@Walter: Thanks, I have posted the code.

texas A&M universdity 2012-1-13

Thanks, That works

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Sean de Wolski 2011-12-27

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在 MATLAB Online 中打开

x(n)= x(n-1)+d;

when n = 1, the first iteration of the loop, you're trying to reference x(1-1) a.k.a. x(0) which is undefined and the reason you're seeing the above error.