If you can read this and see the IJulia logo in the top left corner of the browser window, congratulations! You are ready to start using Julia.
This IJulia notebook is fully executable. The Julia code is grouped into units called cells. To run all the commands in a cell, click inside and press Shift+Enter.
In [ ]:
1+1
Try changing the code to see what it will do!
In [2]:
println("Hello world")
You can also use the print() function, which does the same thing, but leaves out the newline at the end.
In [3]:
print("Hello")
print("world")
Don't forget the enclosing parentheses, or you will get an error:
In [16]:
print 1+2
In [17]:
print(1+2)
You can print multiple things together. Separate each piece with commas:
In [19]:
print("1 + 1 = ", 1+1)
Note: Julia does not automatically insert spaces when printing multiple items together:
In [23]:
println("For","sooth!","There is no ",1," I trust more", ".")
In a REPL such as this IJulia notebook, Julia will automatically print the result of the last statement. This will not happen if you run julia in a non-interactive mode.
In [24]:
1+1
2+2
Out[24]:
However, a print or println function will always produce printable output.
In [26]:
1
2
print("3")
4
5
Out[26]:
Some special characters are produced by escape sequences. An escape sequence starts with a backslash \ and ends with a single character that follows it.
Here are two very common examples:
In [53]:
println("1\n2") #Newline
println("1\t2") #Tab
To print the baskslash character itself, it has to be escaped with another backslash.
In [54]:
println("1\\2") #backslash
The dollar sign has special meaning in Julia and must be escaped to print correctly.
In [74]:
println("\$")
Julia supports Unicode characters, which are used to encode non-English texts and special symbols.
In [15]:
println('∑')
In Julia, a single character is quoted with single quotes ('), whereas strings are enclosed by double quotes (").
The following will produce an error in Julia:
In [8]:
println('Hello')
Here is the first article of the UN Declaration of Human Rights in Chinese:
In [6]:
print("人人生而自由，在尊严和权利上一律平等。他们赋有理性和良心，并应以兄弟关系的精神相对待。")
To specify a Unicode character by its code point:
a) use \U followed by its hexadecimal code point.
In [12]:
print('\U263A')
or, b) use the char() function.
In [2]:
char(0xa22d)
Out[2]:
In [ ]:
Julia provides the `is_valid_char()` function to check if a valid character was specified.
In [1]:
println(is_valid_char(0x110000))
println(is_valid_char(0x1100))
Sometimes the character won't display correctly. This is usually a problem with the font you are using.
You can try your luck with the Unicode character for a slice of pizza:
In [33]:
println('\U1f355')
In [28]:
print("The jail still held the heart I lost and the finger I stole") #from you
(This example sentence was taken from [here](http://www.essayscam.org/Forum/17/ellipsis-4109/).)</small></small>
Comments are useful for leaving notes about code that is tricky or potentially confusing, and for temporarily disabling part of Julia programs.
In [31]:
println("Roses are red")
println("Violets are blue")
#println("I don't like bread")
println("One plus one is ", 1+1) #Compute the answer
In [40]:
println("+1 = ", +1)
println("-1 = ", -1)
println("1 + 1 = ", 1+1)
println("1 - 1 = ", 1-1)
println("2 * 3 = ", 2*3)
println("2 / 3 = ", 2/3) #The answer is not a whole number!
println("3 \\ 2 = ", 3\2) #Same as above
println("2 ^ 3 = ", 2^3) #This is exponentiation
Remainders are slightly trickier, particularly when it comes to negative numbers.
In [58]:
println("5 % 2 = ", 5%2)
println("rem(5,2) = ", rem(5,2)) #Same as above
println("mod(5,2) = ", mod(5,2))
In [64]:
println("5 % 2.5 = ", 5%2.5)
println("rem(5,2.5) = ", rem(5,2.5)) #Same as above
println("mod(5,2.5) = ", mod(5,2.5))
In [59]:
println("-5 % 2 = ", -5%2)
println("rem(-5,2) = ", rem(-5,2)) #Same as above
println("mod(-5,2) = ", mod(-5,2))
For convenience, you can use underscores (_) to separate groups of digits.
In [12]:
525_600 #Five hundred twenty five thousand six hundred
Out[12]:
In [11]:
1_00_00_000 #One crore = 10^7
Out[11]:
In [65]:
println("1 / 0 = ", 1/0)
In [6]:
z=3+4im
z' #conjugate
Out[6]:
In [8]:
z*z'
Out[8]:
In [13]:
i=2.0
Out[13]:
In [15]:
supercalifragilisticexpialidocious = pi
supercalifragilisticexpialidocious/2
Out[15]:
In [17]:
e = 1+1im
Out[17]:
In [27]:
z=3+4im
ξ=1/z
Out[27]:
In [30]:
アルコール = 0.1337
アルコール^2
Out[30]:
You can even use names of built-in variables and functions, if you so choose. (This is usually not a good idea since it is very easy to write confusing code.)
In [31]:
im=2
3+4im
Out[31]:
You cannot, however, use the names of Julia keywords for your variable names.
In [23]:
end=0.5im
In [33]:
x=1
x==2
Out[33]:
To test inequality, use !=:
In [35]:
x!=x+1
Out[35]:
In [ ]:
Printing variables
In [ ]:
There are a few ways to print variables in Julia:
In [ ]:
g=9.81
In [ ]:
In [1]:
f(x::Number, y::Number) = (x,y)
f(1,2)
Out[1]:
In [2]:
f(x::String, y::String) = string(x,y)
f("foo","bar")
Out[2]:
In [4]:
f(x,y) = f(string(x),string(y))
f("I like ",1π)
Out[4]:
Introspection
In [5]:
methods(f)
Out[5]:
Declaring types
In [6]:
type LP
c # Types are optional
A::Matrix{Float64}
b::Vector{Float64}
end
randlp(n,m)=LP(rand(n),rand(n,m),rand(m))
mylp = randlp(10,5)
println(mylp.c)
Parametric types
In [9]:
type LP2{T}
c::Vector{T}
A::Matrix{T}
b::Vector{T}
end
In [10]:
lp = LP2{Float64}(mylp.c,mylp.A,mylp.b) # dbl precision
lp = LP2{Rational}(mylp.c,mylp.A,mylp.b) # exact
Lists
In [11]:
L = {} # empty Vector{Any}
push!(L,3.0)
Out[11]:
In [12]:
L2 = Float64[] # Vector{Float64}
push!(L2,:Hello) # Error
In [13]:
push!(L2,10.7) # Okay
Out[13]:
In [14]:
L3 = Float64[2,3,4]# conversion
Out[14]:
Dictionaries
In [15]:
d1 = Dict() # Empty untyped
d1[“key”] = 10 # Okay
In [17]:
d2 = (Symbol=>Int)[] # Empty typed
d2[:x] = 8 # Okay
d2[10] = "value" # Error
In [19]:
d3 = [:Cat=>13, :Dog=>14]
d3[:Dog]
Out[19]:
Exercise!
Write a function that takes a vector and normalizes it in place by its L2 norm. Use for loops.
In [20]:
f(v) = v/norm(v)
Out[20]:
In [ ]:
In [ ]: