MATLAB

Course notes

Notes from when I took Mike X’s course as a refresher for CSHL Neural Data Science summer school.

Course: Mike X Cohen’s course on Udemy

GUI

• Can set more information for variables. Recommended information to add apart from variable name and value is: size, bytes, type.

Variables

• Type character array and string are different. Basically best not to use string type. Not sure what it is used for.

  s1 = 'char_array';
  s2 = "string";
  s1(2) % gives 'h'
  s2(2) % gives an error

• Reminder: Square (array) allows concatenation. Cell arrays on the other hand will create cells for every value between the curly brackets

  ['Hello' 'World']
  [4:9 10:11 pi]
  % above from different
  { 4 5 6}
  {'Hello' 'World'}

• Multiline comments (to use if needed)

  %{
  Can write anything here as many lines as I want!
  }%

• Structures
  Good use of structures to replace “objects”. The nice part of this is that you can make struct arrays with particular types of elements.

  struct(1).name = "Tom"
  struct(1).age = 30
   
  struct(2).name = "Ron"
  struct(2).age = 45

Functions

Mike talks about a nice way of writing functions. Starting with comments to describe the algorithm the filling in the details. This is a nice way of forcing writing down the algorithm before coding (which often is the cause of long/confusing code).

Read and writing

• Can read ‘clean’ text files using load. Also can use the standard, xlsread (or csvread), or just load for matlab files

  load('data.txt')

• dlmwrite allows to write data with any defined delimiters \t for tab or space or comma. csvwrite is a specific instance of this.

Plotting

• imagesec - good for visualizing matrices

Debugging

• Use 1i instead of i (will get confused with for i iterator)
• .* works as element to element multiplication only if the matrix are of the same sizes (row, col numbers). If the row columns are flipped, matlab will silently do a outer product multiplication.
• tic-toc
  • can use to measure how long a few lines of code take to run.
• matlab profiler
  • a nice way of measuring how much different lines of code take
  • seems super useful actually
  • not sure why I was not using it 😅
  • there seems to be some tmpscript issue - that is code needs to be moved to a file called tmpscript. Not sure if this has to be exactly the specific one or just any script file.

Tips

• From 2019/2020, there is an addon manager which one can use to install toolboxes you want, so no need for a 30GB all toolbox install anymore! You will have to sign in with your account though, but the storage save is massive.

• Archlinux + sway
  For sway, you need to enable _JAVA_AWT_WM_NONREPARENTING=1. Although you might have defined it in the environment, for some reason running matlab from commandline does not automatically use the variable. Create a desktop entry, which seems to work well, or use the following line:

  Exec=env _JAVA_AWT_WM_NONREPARENTING=1 matlab