Julia for Matlab and Python Users (Updating)

Motivation

Julia is a very fast language.

Julia hybrids many features from many sources. Here I’m taking note on its syntax and features by comparing to Python and Matlab.

Basic Functions

• print is like in python BUT, no \n added at the end of each line. println has the \n
• String formatting is super easy, we can just use values of expressions.
  • "$greet, $whom.\n"
  • "1 + 2 = $(1 + 2)"

Operators

• . operation extend its usage in matlab it means to vectorize sth. or broadcast one operation to all the element of the argument.
  • This is super powerful, extending beyond arithmatics. You can broadcast everything by putting a . there.
• ... is like * in python, it could de-bundle a tuple or list into lots of variables.

Types

• :: signify the type of sth.
• <: signify the type is a subtype of X.
• nothing equiv to None in python
• Similar to matlab true false not capitalized.

Control Flow

• Control flow syntax is much like matlab if...elseif...end no indentation or :.
• Loop syntax is a bit like Python for .... in ..., with some caveat
  • But if there are two things being looped, there needs to be a () , not like python.
    • for (i,x) in enumerate(L)

Functions

• Syntax is like

  • function f(x,y)
        x + y
    end
    

• Lot’s of ways to write inline functions

  • f(x,y)=x+y defines a function!
  • x -> x^2 + 2x - 1 is a nameless function, useful for map or filter

• Return values

  • julia default supports no return, it automatically returns the output of last expression.

• Type decoration and Argument types.

  • Here keyword arguments are separted by ;, not like python.
    • function plot(x, y; style="solid", width=1, color="black")
  • Giving a default value for arguments will not make it a keyword argument.
    • Date(y::Int64, m::Int64=1, d::Int64=1)

• Docstring

  • Unlike python, docstring lives above the function signature not below.

class, struct

There is no real class in julia as in python or matlab. There is only struct and the methods. This is a design choice.

struct owns the data it has, but does not own the methods or functions of it. Functions have the freedom to change.

You do not need to re define a class for re define one of its method.

The constructor syntax is like.