You can use ind2sub as suggested in the answer posted by @Jaynik. But as they wrote that code, they hard-coded the number of dimensions in the array B. I'll show you how we can relax that to get the information at run-time not at write-time.
Sample data
First let's make some data whose dimensionality we don't know when we write the code. This is going to create an array with between 2 and 6 dimensions, each of which is of length between 3 and 7.
numberOfDimensions = randi([2 6])
sizeOfData = randi([3 7], 1, numberOfDimensions)
A = rand(sizeOfData);
Linear indexing
Now we could get an arbitrary individual element of A using a linear index.
whichElement = randi(numel(A))
xLinear = A(whichElement)
Subscripted indexing
But how would we do this with subscripted indexing? I don't know how many dimensions A will have as I type this. But I can get that information using the ndims function.
n = ndims(A);
Comma-separated list
Now that's how many output arguments I should use when I call ind2sub. But how do I dynamically call it with some number of arguments? I can use a comma-separated list created from a cell array.
subscripts = cell(1, n);
[subscripts{:}] = ind2sub(size(A), whichElement) % essentially equivalent to
% [subscripts{1}, subscripts{2}, ...] = ind2sub(...)
I can use that comma-separated list as the set of subscripts in my indexing expression.
xSubscripted = A(subscripts{:})
Let's check that the two indexing operations gave the same result.
check = isequal(xSubscripted, xLinear)
Handling of : as an index
For indexing in particular, you can take advantage of something that I think was introduced for object-oriented programming. A ':' index gets all the data in that dimension. For example, to get all the rows in A:
subscripts2 = subscripts; % So you can compare with the original subscripts cell
subscripts2{1} = ':'
xAllRows = A(subscripts2{:}) % Equivalent to A(:, something, ...)
Note that the only hard-coded numbers in this example occurred in the "Sample data" section (the size inputs to randi and the 1 to make a row vector to use as the size data in the rand call), the 1 in the cell call in the "Comma-separated list" section to make a row vector cell array, and the 1 in the "Handling of : as an index" section (to say I wanted all the data in the first dimension.) Everything else is computed from qualities of the array A.
