#Permute matlab code#

There exist built-in functions in MATLAB to convert subscript indices to linear indices, and vice versa: sub2ind and ind2sub respectively. So M(2) is the second element of the first column which is 3 and M(4) will be the first element of the second column i.e. Note that arrays are stored in column-major order in MATLAB which means that you access the elements by first going down the columns. You can directly access the first element: > M(1) MATLAB allows you to treat n-dimensional arrays as one-dimensional arrays when you index using only one dimension.

To do this we must consider linear indexing. > M(, )įor example subscript indexing cannot extract only the elements M(2,1) or M(3,3). Subscript indexing can be restrictive as it will not allow to extract single values from different columns and rows it will extract the combination of all rows and columns. So if you want all the columns from column 2 to the last column, you can use write the following: > M(2, 2:end) The end keyword will work exactly as if it was the number of the last element in that dimension. MATLAB also provides a shortcut for specifying the last element of a dimension in the form of the end keyword.

#Permute matlab code#

For example, the following code will also return the entire second row > M(2, :) To select an entire row (or column), MATLAB provides a shortcut by allowing you just specify. In MATLAB, the vector is more easily created using the colon operator, i.e. For example to get the entire second row, we can specify that we want the first, second and third columns: > M(2, ) You can index multiple elements at once by passing a vector for each coordinate instead of a single number. Moreover, MATLAB indices starts with 1 and not 0 like most programming languages. Note that the order of subscripts is the same as the mathematical convention: row index is the first. The number of subscripts provided exactly matches the number of dimensions M has (two in this example). For example, accessing the element on the second row and third column: > M(2, 3) The most straight-forward method for accessing an element, is to specify its row-column index. These three methods are now explained in more detail using the following 3-by-3 matrix M as an example: > M = magic(3)

Logical indexing - where you use a logical matrix (and matrix of true and false values) with the identical dimensions of the matrix you are trying to index as a mask to specify which value to return.

That means, you specify each position in the matrix with a single number.

Linear indexing - where the matrix is treated as a vector, no matter its dimensions.

Subscript indexing - where you specify the position of the elements you want in each dimension of the matrix separately.

MATLAB allows for several methods to index (access) elements of matrices and arrays: