Beginner MATLAB Course for Neuroscience and Psychology

Indexing is selecting a subset of elements from the matrix, in other words, it let's you get the part of a matrix that you want.

How to do it?

The easiest way to index something is to type the name of the variable you want to take something from and then specify the position of the element you want to index in round brackets. You can also use indexing to put new values into your variables.

When indexing a matrix, you can use two values, the first to specify the row and the second to specify the column.

In MATLAB, you can do basic maths on numbers or on variables. So your variables will be treated just like the numbers they represent.

Most symbols are what you would imagine them to be. Keep in mind that in MATLAB we use a star * to multiply things and a slash / to divide thighs - but an important thing to note is that a star (*) symbol on its own means matrix multiplication and a slash (/) on its own means matrix division.

Now, remember that in MATLAB we can work with both scalars and matrices and if you want to do a scalar multiplication or division, then we need to put a dot next to a star or slash.

You can also do sums between a scalar and a matrix. The sum will be applied to every value of the matrix.

Another way of doing basic maths in MATLAB is to use functions and we will talk about basic functions in the next lesson.

MATLAB has a large number of built-in functions that can help you perform maths or statistics and can also generate matrices quickly and easily.

Essentially, a function is a set of commands that get some inputs and give some outputs. Using the name of a function in a command window lets you run all the code within that function.

For the function to work, you need to put your inputs otherwise known as arguments in round brackets and after the function name.

All functions written by MATLAB have help files to tell you how to use them. To get the help files, you need to type help followed by the command name.

Logical operators are used to decide which part of a code to run next or which elements of a matrix to use in a calculation.

These are the main logical operators and their signs:

> greater than

< lesser than

== is equal to

~= is not equal to

~ not

=< less than or equal to

=> greater than or equal to

& and

| or

When you give MATLAB two values with one of the logical operators in the middle, it can tell you if a statement is true or false using the numbers 1 and 0. False is represented by 0 and true by the number 1.

This kind of response is called "Boolean logic".

Any MATLAB command you write into the command window can also be written into a script.

A script is a list of commands executed one after another in the order they appear on the screen.

You can easily run your script just by typing the name of the script file in MATLAB command window.

To make a script, type the MATLAB function edit and hit return or click on the ‘new script’ icon in the top left corner.

Pixels and Images: A pixel is a unit (typically square) of digital information. The pixels are laid out in a grid, which is an image. In Matlab, an image is a matrix. You can think of each element of a matrix as a pixel.

Bit: a bit is a digit in the binary number system. It can be 0 or 1. 8 bits = 1 byte.

Pixel depth: a bit is a unit of color information in a pixel.

Buffer and ‘Flip’: A buffer is temporary storage. In the present context, what you will do is

prepare what you want to display on the on screen window in a back buffer (off screen) and

then copy the contents to the on screen. You can create as many off screen windows as you want.

Screen: add loaded function that will be used in almost every experimental program with Psychtoolbox.

To get help, type: Screen OpenWindow?

In this Lecture, you will learn how to draw graphs using Matlab.

We will analyse a set of data and show you step-by-step how to use simple lines of code to draw any graph.

We will go through different types of graphs, show you how to change colours and edit your figure.

In this lecture, we will cover main tools and functions.

You will learn when you to use them and how to incorporate into your script these functions:

• if

• switch

• while

• for

You will be given an example of these functions in a code to see what they do.

1. If  - very useful command and the most basic element. If the logical statement you have is true, the next line of the code will be executed. If it is not true, it will move into the else line, which will have a different outcome.

2. For -  if you want to repeat a cycle and run the same script, use for. It will execute the set of commands several times. You may write how many counters you want to have

>> for i=1:3

A(i)=i*2

End

A= 2

A= 4

A= 6

3. Switch – this command will allow you to check which situation is correct. You may have several possibilities (cases) and the script to run associated with that case. If none of the logical alternatives is logical, there is a line otherwise that will execute a code you write.

For example, >> A=5

switch(A)

  case 1

    disp(‘A is a number’)

  case 3

    disp(‘A is letter’)

  case 5

    disp(‘A is five’)

otherwise

   disp(‘A is not one or three or five’)

end

‘A is three’

4. While is similar to for loop, however, it will repeat the same loop several times while the statement is correct. Let’s write a code with values for y while x value is 2

>> x = 2

Y = -6

While (x==2_

y=y+1

if(y>1)

x=2

end

end

y=…%run this code and modify the values, see what happens

5. Try…Catch – although it is not a code, you may use that to catch the error and prevent your computer from crashing.

In the next step, you will learn how to create your own function and add it to your script:

To write a function, start with this and follow the same format

>>[outputs] = function_name(inputs)

If you want to check, from where your function is taken, in other words, you want to check which path it is, type

>> path

Then select the Set path on the file menu. If you are not sure which command is chosen to execute, type

>> which

In this lesson, you will learn how to code an if loop to check whether a variable meets logical conditions. One example will involve numbers, colours (string variables) and a logical operation ''for''.

Well done, guys! You have now completed the Beginner MATLAB course! You can download the lecture slides attached in the resources.

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