Matlab Tutorial 2: Matrices in Matlab

Matrices in Matlab

In the previous tutorial we have used the concept vector. This is a special case of matrix. A two-dimensional matrix is nothing but a rectangular table with its elements ordered in rows and columns. A matrix mxn consists of m rows and n columns. In Matlab this can be written for a matrix A.

>> C=[ x' y1' y2']

C(:,1) % : means all rows and 1 stands for the first column.
C(2,:) % means the second row and all columns.

This matrix A has 2 rows and 3 columns. The first row is: 1 2 3 and the second: 4 5 6 . For the columns we have the have following order: Column 1: 1,4 column 2: 2,5 and finally column 3: 3,6

Each entry in the matrix A is accessible by using the following indices:

>> plot(C(:,1), C(:,2),C(:,1),C(:,3)), grid

For instance try the following :

>> ones(3) % Gives a quadratic matrix, with three columns and three rows
% only containing ones.

or

>> ones(3,5) % Same as above, but with three rows and five columns.

The most common matrix in matlab is the two-dimensional one. Many of the commands in matlab are only for valid for such matrices. The arithmetic operators (+, -, *, / and ^) that we used in tutorial1 can also be applied for matrices, but we also have some others as well.

Exercise 1: Vectors in Matlab

Generate a vector x=[5, -4, 6 ] with three elements. In Matlab as:

>> zeros(2) % Gives a quadratic matrix 2X2, and with zero as elements.

or alternatively

>> eye(3) % Gives the unity matrix with ones on the main diagonal.

What is the answer of x(4) and x(0) ?

The indices in a vector starts from 1 and in this case ends with 3. Therefore to ask for x(4) and x(0) is pointless. Suppose we would have done differently creating the vector x. Read more »

Matlab Tutorial 1: Hello world, plotting, mathematical functions and file types

In this first Matlab tutorial, I will try to show you the basics of Matlab user interface, data types, simple functions and mathematical operations. All with basic examples so that anyone with any level of programming knowledge can start using Matlab as a mathematical laboratory.

Matlab User Interface

Start Matlab by a double click on the Matlab icon or else by searching for it under program. Now, there should be a large window containing several smaller. These could for instance be:

• Command Window
• Command History
• and Workspace.

This will of course depend on what version you are currently working in. This is the desktop of Matlab.

Command Window: Here you can write your own command lines and access your own files (m-files), but normally you can also see the output from the calculations in this window.
Command History: All command lines are saved here and can be seen in the window, but the same can be achieved by using the arrow button (up). The past command lines can the be seen in the command window.
Workspace: The variables that have been used or created during the execution will be shown in this window. Here you can see value, bytes and class. When you double click on the variables, the elements of the variables become visible.

These three windows should be the default when you start Matlab. Read more »