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First codes

First codes#

Variables and types#

A variable, in Julia, is a name associated (or bound) to a value. It’s useful when you want to store a value (that you obtained after some math, for example) for later use. For example:

# Assign the value 10 to the variable x
x = 10

# Doing math with x's value
x + 1

# Reassign x's value
x = 1 + 1

# You can assign values of other types, like strings of text
x = "Hello World!"

"Hello World!"

println(x)

Hello World!

Allowed Variable Names#

Para los nombres de variables pueden ocupar letras, número y símbolos. Deben tener cuidado con algunas excepciones que están reservadas, por ejemplo el número pi, o funciones específicas que no se pueden modificar o que no queremos modificar, por ejemplo if, else, while, sum, mean, etc.

🍎 = 10 
α = 0.1 
Δ = 5 
🌵 = 20 

println((π, 🍎, α, Δ, 🌵))

(π, 10, 0.1, 5, 20)

Stylistic Conventions#

As suggested by Julia’s recommendations:

While Julia imposes few restrictions on valid names, it has become useful to adopt the following conventions:

  • Names of variables are in lower case.

  • Word separation can be indicated by underscores (‘_’), but use of underscores is discouraged unless the name would be hard to read otherwise.

  • Names of Types and Modules begin with a capital letter and word separation is shown with upper camel case instead of underscores.

  • Names of functions and macros are in lower case, without underscores.

  • Functions that write to their arguments have names that end in !. These are sometimes called “mutating” or “in-place” functions because they are intended to produce changes in their arguments after the function is called, not just return a value.

Types#

Types will be a fundamental part of programming in Julia; they are flexible and will provide flexibility when programming and solving a problem.

Types correspond to a category of values with specific characteristics. So far, we have seen two different types: integer and string.

As the course progresses, we will introduce different types. The basic ones we will use include: integers, floats, strings, arrays, and booleans.

To see what type a variable is, you can use the function typeof(variable).

a = 10 
b = 10.0 
c = "Hello"
d = [1,2,3]
e = true 
f = [a,b]
g = [a,b,c]

println("a: ", (a, typeof(a)))
println("b: ", (b, typeof(b)))
println("c: ", (c, typeof(c)))
println("d: ", (d, typeof(d)))
println("e: ", (e, typeof(e)))
println("f: ", (f, typeof(f)))
println("g: ", (f, typeof(g)))

a: 

(10, Int64)
b: (10.0, Float64)

c: ("Hello", String)

d: ([1, 2, 3], Vector{Int64})
e: (true, Bool)
f: 

([10.0, 10.0], Vector{Float64})
g: ([10.0, 10.0], Vector{Any})

Mathematical Operations#

  • Standard mathematical operations

  • Arrays: Vectors and Matrices

  • Logical operations

Standard mathematical operations#

Basic mathematical operations:

  • Addition (+)

  • Subtraction (-)

  • Times (*)

  • Divide (/)

  • Inverse divide (\ )

  • Power (^)

  • Remainder (%)

a = 10 
println("+: ", a+a)
println("-: ", a-a)
println("*: ", a*a)
println("/: ", a/a)
println("^: ", a^a)
println("% :", a%a)

+: 20
-: 0
*: 100
/: 1.0
^: 10000000000
% :0

Arrays: Vectors and Matrices#

https://docs.julialang.org/en/v1/manual/arrays/

x = [1,2,3]

3-element Vector{Int64}:
 1
 2
 3

x = [1 2 3]

1×3 Matrix{Int64}:
 1  2  3

x = zeros(5,5)

5×5 Matrix{Float64}:
 0.0  0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0  0.0
 0.0  0.0  0.0  0.0  0.0

v = ones(3,3)
w = [1,2,3]
x = v*v
y = v.*v
z = x*w

println("x: ", x)
println("y: ", y)
println("z: ", z)
println("sum: ", sum(z))

x: 

[3.0 3.0 3.0; 3.0 3.0 3.0; 3.0 3.0 3.0]
y: [1.0 1.0 1.0; 1.0 1.0 1.0; 1.0 1.0 1.0]
z: [18.0, 18.0, 18.0]
sum: 54.0

Logical operations#

1 == 1

true

true || false

true

true && false

false

x = 10
y =  x < 20

true

  1. Create a variable xmin equal to 1 and a variable xmax equal to 100.

  2. Create a variable x that contains equidistant values from xmin to xmax.

  3. Check the type of x.

  4. Create a variable y that indicates whether each element in x is greater than 50. Hint: It should be of type BitVector.

  5. Create a variable z that divides each element of x by each element of y.

  6. Determine the maximum value of the vector z and find out which function can be used to obtain it.

  7. With the variables A = rand(3,3) and B = ones(3,3), test the operations * , ^, .* , -, inv(), det(), and the difference between / and \ .

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