>>> index exceeds the number of array elements. index must not exceed 1..

In this blog post we are looking to resolve an error that can occur in MATLAB: index exceeds the number of array elements. index must not exceed 1. This is how our article will be organized.

• How to cause the error index exceeds the number of array elements. index must not exceed
• Meaning of the error
• How to fix the error in MATLAB

How to cause the error index exceeds the number of array elements. index must not exceed 1. ?

To reproduce the error in MATLAB you can for example run this code

y = zeros(6,1);
dy = zeros(6,1);
K = 10^(8);
d=5*10^(-1);
r=10^(-1);
for i = 1:6
    ii     = 4 * (i-1) + 1;
    dy(ii) = r * y(ii) * (1 - (y(ii) + y(ii+1)) / K) - d * y(ii+2) * y(ii);
end

In this example i’m getting « Index exceeds the number of array elements. Index must not exceed 6. »

Meaning of the error

This error is quite classic, it means that you are trying to access an element in an array/matrix whose index exceeds the maximum index. Example you have an array of 6 elements and you are trying to access the 7th. In this case you get this error « Index exceeds the number of array elements. Index must not exceed 6. »
In our example above we can easily check the value of ii which is calculated from i to check if it exceeds i. For that I adapt code by adding a disp of ii :

y = zeros(6,1);
dy = zeros(6,1);
K = 10^(8);
d=5*10^(-1);
r=10^(-1);
for i = 1:6
    ii     = 4 * (i-1) + 1;
    disp(ii)
    dy(ii) = r * y(ii) * (1 - (y(ii) + y(ii+1)) / K) - d * y(ii+2) * y(ii);
end

We are getting this result :

    1

     5

Index exceeds the number of array elements. Index must not exceed 6.

Error in untitled (line 9)
    dy(ii) = r * y(ii) * (1 - (y(ii) + y(ii+1)) / K) - d * y(ii+2) * y(ii);

>> 

In fact look at :

dy(ii) = r * y(ii) * (1 – (y(ii) + y(ii+1)) / K) – d * y(ii+2) * y(ii);

and if you check the workspace you will see that y is an array of 6 elements then you are trying to access to y(7). 7 exceed the size of the max index 6.

How to fix the error in MATLAB

First of all, I would like to draw attention to the fact that you don’t have to add displays. You can use the matlab debugger via:

dbstop if error

Also in our case we saw that the error was accessing the array/matrix via an index that exceeds its size. In our case, the loop causes it to access row 7 of a table with a size of 6.

To guard against such a problem, one solution is, for example, to test via conditions if we exceed the maximum index and if so it is replaced by the max index. Example :

dbstop if error
y = zeros(6,1);
dy = zeros(6,1);
K = 10^(8);
d=5*10^(-1);
r=10^(-1);
for i = 1:6
    ii     = 4 * (i-1) + 1;
    if ii >= 5
        ii=4
    end
    dy(ii) = r * y(ii) * (1 - (y(ii) + y(ii+1)) / K) - d * y(ii+2) * y(ii);
end