matrix - Is MATLAB row specific or column major?

Question

In MATLAB, we can operate on both rows and columns of a matrix. What does it exactly mean by "row major" or "column major"?

Answer 1

It is important to understand that MATLAB stores data in column-major order, so you know what happens when you apply the colon operator without any commas:

>> M = magic(3)
M =
     8     1     6
     3     5     7
     4     9     2
>> M(:)
ans =
     8
     3
     4
     1
     5
     9
     6
     7
     2

I tend to think "MATLAB goes down, then across". This makes it easy to reshape and permute arrays without scrambling your data. It's also necessary in order to grasp linear indexing (e.g. M(4)).

For example, a common way to obtain a column vector inline from some expression that generates an array is:

reshape(<array expression>,[],1)

As with (:) this stacks all the columns on top of each other into single column vector, for all data in any higher dimensions. But this nifty syntactic trick lets you avoid an extra line of code.