Why am I getting the error "Array indices must be positive integers or logical values"?

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Yogesh Pai
Yogesh Pai 2018-12-5
编辑： MathWorks Support Team 2024-10-21，17:21
Ran in:
I want to compare the exponential of matrix "A" obtained by the summation formula and the one with the eigen values. However, I'm getting the following error when exponential is computed with the diagonalised form (E here). 
Array indices must be positive integers or logical values.
A = [1,2,1,3; 3,1,2,0; 2,2,1,4; 1,3,2,1]; [V,D] = eig(A); exp_A = 0; for k = 0:100 exp_A = exp_A + (A^k)/factorial(k); end disp(exp_A); 304.3054 340.7344 263.9243 320.0369 275.4796 308.2690 238.7711 289.0775 389.2552 436.7654 339.1998 410.7063 309.9581 347.7556 269.7020 326.5840 E = V*(exp(D))\V; disp(E); 0.0008 + 0.0000i -0.0001 - 0.0000i -0.0001 + 0.0000i -0.0007 - 0.0000i -0.0001 - 0.0000i -0.8364 - 0.1567i 0.1039 + 0.0000i 0.8393 + 0.1795i -0.0001 + 0.0000i 0.1039 + 0.0000i -0.8364 + 0.1567i 0.8393 - 0.1795i -0.0007 - 0.0000i 0.8393 + 0.1795i 0.8393 - 0.1795i -0.7766 - 0.0000i
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Kelly Kearney
Kelly Kearney 2024-10-21
编辑：MathWorks Support Team 2024-10-21，17:21
MATLAB uses 1-based indexing, so the first element is accessed with index 1, not 0. This means array indices must be positive integers. For example, access the first element of a vector "A". 
A = [10, 9, 8, 7, 6]; Aval = A(1) % This returns 10. Meanwhile, A(0) returns an error.
MATLAB also accepts logical indexing, which can be useful when working with conditional statements. For example, say you want to know the values of "A" that is larger than 7. Use the > operator to return a logical array whose elements are logical 1 when an element in "A" is larger than 7; and logical 0 otherwise. 
ind = A > 7
Now that you know the locations of the elements meeting the condition, you can access the individual values that are larger than 7 by using "ind" as the index array. 
Avals = A(ind)
For more information, see Array Indexing. 
As others have mentioned, without providing the full code that caused the error, it is hard to pinpoint why this error occurs. For example, you can have a variable named "sum = 2" sitting in your workspace. So, when you try to call the built-in "sum" function to find the sum of array elements, such as "sum(0.1:0.1:1)", the existing variable is overshadowing it. The error occurs because MATLAB cannot extract the element with index 0.1, 0.2, and so on. To avoid this error, you should not use a variable name that conflicts with MATLAB built-in functions. 

更多回答（9 个）

Roya Kakar
Roya Kakar 2022-1-19
Please answer my quesion. I get the following error after running this line of code
sm =sum(table2array(X));
Array indices must be positive integers or logical values.
henry espinoza
henry espinoza 2020-6-19
Array indices must be positive integers or logical values.
Error in Tarea3_HE (line 15)
Xc1 = (-1 /(PRM(u)*(w)))*j
laura celis
laura celis 2022-3-12
tengo este error
Array indices must be positive integers or logical values.
Error in recortedesenales (line 38)
z1= z(A:B);
Roshan Siwakoti
Roshan Siwakoti 2022-10-21
a(i) =((delta_p2)/(2*tau(j)*(t_traj(j+1)-t_traj(j))))-((delta_p1)/(2*tau(j)*(t_traj(j)-t_traj(j-1))))
Array indices must be positive integers or logical values
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Kelly Kearney
Kelly Kearney 2022-10-21
Possible guess... Is a(i) supposed to be a(j)? If you haven't otherwise set i to be an integer, it defaults to sqrt(-1), which cannot be used as an index. Same goes for j; check that it's an integer. Best practices in Matlab recommend avoiding i or j as indices for this very reason.

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Ferlyn
Ferlyn 2022-11-14
% c. x(t) = 3*exp(-2*t)u(t)
subplot (4,2,3)
y = 3*exp(-2*t).*(u(t));
plot (t,y,'-g','Linewidth', 2);
axis ([-1 5 -1 5]);
grid on;
xlabel ('t in sec');
ylabel ('x(t)');
title ('plot of (c)');
Here's my code and it says "Array indices must be positive integers or logical values". What should I do to fix it? Thank you.
Nerea Espinosa Giralt
Hola!
Tengo este error." Array indices must be positive integers or logical values."
Atenuacion=(k*R_001^alfa*u(p))*(R_001)^(0.38/Ls-0.25/(1+n(p/0.01)^(-0.36)*longitud^m)*Ls);
¿podriais ayudarme por favor?
Gracias,
Saludos
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Steven Lord
Steven Lord 2022-11-19
Ran in:
The section of code with n(p/0.01) also looks like it might be missing a multiplication operator. If it isn't and you intended p/0.01 to give you an integer value you can use as an index into n, you may encounter difficulties due to floating point arithmetic. Even if that expression did happen to give an integer value (or you called round to force it to give an integer value) as written unless that integer value is 1 you're asking for an element of n that doesn't exist.
x = 1;
y = x(2) % There is no second element
Index exceeds the number of array elements. Index must not exceed 1.

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Fariha
Fariha 2023-8-12
Hello, my code:
yoy(j,1)=100*(log(Real_Price(ii,1))-log(Real_Price(ii-4,1)));
every time I run it says 'Array indices must be positive integers or logical values.'
can you help me understand my problem?
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DGM
DGM 2023-8-12
MATLAB sees that you're trying to index into an array. Array indices must be real positive (nonzero) integers (or logicals). So:
Is the index jj a real, positive integer?
Is the index ii a real, positive integer?
Is ii>4 so that ii-4 is always positive?
Is log() still interpreted as a function, or have you created a variable with the same name?

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Maximilian
Maximilian 2023-8-18
Hello, why am I getting the "Array indices must be positive integers or logical values." error for the code below. I cleared the workspace so that shouldn't be a problem.
Vi = 0;
Vf = 1;
R = 1000;
C = 10 * 10^-6;
t = linspace(0,0.1,1001);
r = R*C;
V(t) = Vi + (Vf-Vi).*(1 - (2.72 .^(-t/r)));
Plot(t,V(t))
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Stephen23
Stephen23 2023-8-19
编辑：Stephen23 2023-8-19
Ran in:
You Index into V using t:
V(t) = ...
Are the values of t valid indices? (hint: no) Get rid of them:
Vi = 0;
Vf = 1;
R = 1000;
C = 10 * 10^-6;
t = linspace(0,0.1,1001);
r = R*C;
V = Vi + (Vf-Vi).*(1 - (2.72 .^(-t/r)));
plot(t,V)
Walter Roberson
Walter Roberson 2023-8-19
It is common to get confused between a formula and an array
A line such as
V(t) = Vi + (Vf-Vi).*(1 - (2.72 .^(-t/r)));
is typically intended to be a formula -- the left and right t are intended to refer to values
MATLAB does support creating formulas with that syntax, but only using the Symbolic Toolbox, such as
syms t
V(t) = Vi + (Vf-Vi).*(1 - (2.72 .^(-t/r)));
MATLAB would then refer to V as a "symbolic function".
MATLAB main support for creating formulas is for numeric formulas (that do not typically involve the Symbolic Toolbox). Those use a different syntax called "anonymous functions" that would look like
V = @(t) Vi + (Vf-Vi).*(1 - (2.72 .^(-t/r)));
In both the case of the "symbolic function" and this "anonymous function", V would become an object describing calculations that would be done if you pass values to the object, such as
V(3.2)
In both the symbolic function and the anonymous function, the t would refer to some indefinite value of t to be given value later, and the symbolic or anonymous function describes how to calculate the output in that future time when you finally get passed a specific value in place of t
But if you are not working with symbolic functions or anonymous functions (or some Object Oriented classes) then () is either for passing parameters to a function, or else for indexing. In the original code
t = linspace(0,0.1,1001);
V(t) = Vi + (Vf-Vi).*(1 - (2.72 .^(-t/r)));
you are working with definite numeric values for t not with a symbolic variable, so the right hand side is calculating definite numeric values, and the left side V(t) would be considered indexing.
Almost any time you have definite numeric values for t, V(t) on the left side of an assignment would be interpreted as an attempt to index. (There are some potential exceptions for Object Oriented classes.)

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Lokesh
Lokesh 2024-6-4
Array indices must be positive integers or logical values.
Error in p3 (line 38)
f_triple_prime(i) = (f(i+1) - 3*f(i) + 3*f(i-1) - f(i-2)) / (deta^3);
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DGM
DGM 2024-6-4
编辑：DGM 2024-6-4
Well, considering that you're the only one that knows what your code does, did you try reading the error and then lookign to see if the given indices are positive integers?

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