3.2.5 Indexing multidimensional arrays

Arrays with multiple dimensions are indexed in the same fashion as one-dimensional arrays we learned about in Section 3.1. The index of each dimension is separated by a comma. For example, the element in the second row, third column of matrix $A$ would be indexed $(2,3)$. Blocks of elements are indexed using the colon notation, just as before. Do the following examples.

% Accessing elements of multidimension arrays
a = 1:12; % define a 1D array
A = reshape(a,4,3) % reshape turns the elements of 'a' into a 4x3 array
                   % we didn't have to initialize A this way, it's just
                   % convenient
A(2,3); % gives 10 (the 6th element of 'A')
A(3:4,2:3) % gives a 2x2 array using the rows 3 & 4 and columns 2 & 3

B = A(:,3:-1:1) % Tricky! How does this work?

B(3,1) = pi % Replace just a single element with pi

MATLAB can handle arrays with any number of dimensions. We will rarely find a use for arrays with more than 3 dimensions. Two- and one-dimensional arrays (matrices and vectors) are at the heart of computational physics, so we'll use these the most.