Element and matrix operations! Working with whole vectors / matrices is not the same as working on elements. unless you specifically want to do matrix algebra you'll usually need the "dotted versions", e.g. .* and ./ Indexing elements Accessing certain parts of a vector/matrix: key idea Use indexing. If you want to get hold of parts of a matrix:: a = [1, 2, 3, 4, 5, 6] specify row and column:: a(1,1) % element at row=1, column=1 a(2,1) % element at row=2, column=1 Indexing (many rows, columns) a = [1, 2, 3; 4, 5, 6] what does the following do? a([1 2],1) % elements at row=[1 2], column=1 a([1 2],[1 3]) % elements at rows 1 and 2, columns 1 and 3 Indexing (tricks) Special tricks to get hold of all rows/columns : (colon) a = [1, 2, 3; 4, 5, 6] specify all rows a(:,1) % elements for ALL rows, column=1 or all til the end of the matrix a(1, 2:end ) % elements at row 1 , columns 2 to end 2 dimensions rows then columns the order in which we think about the data is important! more than 2 dimensions rows, columns, 3rd^\textsf{rd}rd dim, [more dimensions] can think of those by analogy to an Excel spreadsheet? rows, columns, sheets, ... More than 2 dimensions many kinds of data have more than 2d anatomical brain images: 3d (many 2d images) fMRI data: 4d (many 3d volumes) can you think of others? Matlab handles these easily:: V = rand(10, 10, 5); % 10-by-10-by-5 array V(7,8,2) % returns element at that index Storing things other than numbers other kinds of data, not just "numbers" e.g. text is stored as character strings more abstract data types: struct, cell, we'll meet some of them later