MATLAB: Do I get the error “Subscript indices must be real positive integers or logicals?”

error

for k=1:length(x)
d=T(V)-Dft(V)-Dw(V);
end
max = max(d);

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Your line

max = max(d);

first calls upon the built in MATLAB function max to find the maximum of d. It then redefines the name max to be associated with a variable with that value, blocking the use of max as a function. The next time you attempt to take max() of anything, max(d) would be interpreted as an attempt to index the variable named max with the index given in d, which can only work if d is the value true or false or is something numeric that consists entirely of 1's.

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MATLAB: Do I get the error ‘Subscript indices must either be real positive integers or logicals. ‘

This error occurs when you attempt to index into an array using indices that are not positive integers or logical values. Here are some tips for common situations that cause this error message:

1) Double check that your indices are positive integers. Indices in MATLAB cannot be 0, and by default, start with 1.

2) If you are using logical indexing to index into an array, be sure that your index array is of type 'logical', and not a 'double' array of 1s and 0s. You can convert a 'double' array to a logical array before attempting to use logical indexing. For example:

A = [1 2 3 4; 5 6 7 8];
ind_double = [0 1 0 1; 0 1 0 1];
ind_logical = logical(ind_double);
A(ind_logical)

For an index array 'ind', you can check its data type using the 'whos' function:

whos ind

3) If you use floating-point arithmetic to compute an index array, then the array values may not be exact integers. The 'round' function is handy when you know you have an index value that is nearly the integer index that you want. For example,

A = [1 2 3 4; 5 6 7 8];
ind_float = 2.00001;
ind_int = round(ind_float);
A(ind_float)

Below is a way to check if an index array 'ind'' contains exact integer values. This command returns a 'logical' array, where 1 indicates the index value is an exact integer, and 0 indicates it is not.

ind == round(ind)

4) If you assign a variable to the same name as a built-in function in MATLAB, then you will overwrite that function and encounter the error when you attempt to call it. For example,

max = rand(5); 
A = rand(5); 
max(A)

In this event, rename your variable and clear the old one to proceed:

B = max; 
clear max max(A)

For more information on indexing in MATLAB, see the following documentation page:

https://www.mathworks.com/help/matlab/math/array-indexing.html

MATLAB: Sub2ind -> out of range subscript

Your d is 2 x 1, so size(d) is [2 1] . When you use sub2ind(), the data values you provide must be within the size you provide in the second parameter.

Do not use sub2ind() to try to expand a matrix (though you can get away with it by lying about the size of the current last dimension, providing you are expanding on the last dimension.)

Since your second index is always 1 and the data from D is being used as the row number, you do not need sub2ind at all. Just use

d(D,1) = 1;

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MATLAB: Do I get the error ‘Subscript indices must either be real positive integers or logicals. ‘

MATLAB: Sub2ind -> out of range subscript

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