Why Julia?
Contents
Why Julia?¶
Fast
Dynamic, but… optionally typed
Composable (mulitple dispatch)
General Purpose
Open Source
Amazing Packages (e.g. DifferentialEquations.jl, Flux.jl)
Growing community (Slack Workspace)
How fast?¶
Multiple Dispatch¶
my_add(x::Int, y::Int) = x + y
my_add(x::Float64, y::Float64) = x + y
my_add (generic function with 2 methods)
my_add(1, 2)
3
my_add(1.0, 2)
MethodError: no method matching my_add(::Float64, ::Int64)
Closest candidates are:
my_add(::Int64, ::Int64) at In[1]:1
my_add(::Float64, ::Float64) at In[1]:2
Stacktrace:
[1] top-level scope
@ In[3]:1
[2] eval
@ ./boot.jl:373 [inlined]
[3] include_string(mapexpr::typeof(REPL.softscope), mod::Module, code::String, filename::String)
@ Base ./loading.jl:1196
my_add(x::String, y::String) = "$(x) $(y)"
my_add (generic function with 3 methods)
my_add("Hello", "World!")
"Hello World!"
import Base.+
+(x::String, y::String) = my_add(x, y)
+ (generic function with 209 methods)
"Hello" + "World!"
"Hello World!"
struct Point
x::Float64
y::Float64
end
my_add(A::Point, B::Point) = Point(A.x + B.x, A.y + B.y)
my_add (generic function with 4 methods)
A = Point(1.0, 2.0)
B = Point(1.0, 2.0)
my_add(A,B)
Point(2.0, 4.0)
Generic programming¶
using Measurements
x = 5.23 ± 0.14
y = 45.77 ± 0.1
x + y
\[51.0 \pm 0.17\]
Simple pendulum¶
\[
\ddot{\theta} = \frac{g}{L} \theta
\]
using DifferentialEquations, Measurements, Plots
g = 9.79 ± 0.02; # Gravitational constants
L = 1.00 ± 0.01; # Length of the pendulum
#Initial Conditions
u₀ = [0 ± 0, π / 60 ± 0.01] # Initial speed and initial angle
tspan = (0.0, 6.3)
#Define the problem
function simplependulum(du,u,p,t)
θ = u[1]
dθ = u[2]
du[1] = dθ
du[2] = -(g/L)*θ
end
#Pass to solvers
prob = ODEProblem(simplependulum, u₀, tspan)
sol = solve(prob, Tsit5(), reltol = 1e-6)
# Analytic solution
u = u₀[2] .* cos.(sqrt(g / L) .* sol.t)
plot(sol.t, getindex.(sol.u, 2), label = "Numerical")
plot!(sol.t, u, label = "Analytic")
InterruptException:
Stacktrace:
[1] optimal_ticks_and_labels(ticks::Nothing, alims::Tuple{Float64, Float64}, scale::Symbol, formatter::Symbol)
@ Plots ~/.julia/packages/Plots/cPJQu/src/axes.jl:197
[2] get_ticks(::Symbol, ::Vector{Float64}, ::Vector{Any}, ::Tuple{Float64, Float64}, ::Vararg{Any})
@ Plots ~/.julia/packages/Plots/cPJQu/src/axes.jl:320
[3] get_ticks(sp::Plots.Subplot{Plots.GRBackend}, axis::Plots.Axis; update::Bool)
@ Plots ~/.julia/packages/Plots/cPJQu/src/axes.jl:241
[4] get_ticks
@ ~/.julia/packages/Plots/cPJQu/src/axes.jl:224 [inlined]
[5] _update_min_padding!(sp::Plots.Subplot{Plots.GRBackend})
@ Plots ~/.julia/packages/Plots/cPJQu/src/backends/gr.jl:888
[6] iterate
@ ./generator.jl:47 [inlined]
[7] _collect(c::Matrix{AbstractLayout}, itr::Base.Generator{Matrix{AbstractLayout}, typeof(Plots._update_min_padding!)}, #unused#::Base.EltypeUnknown, isz::Base.HasShape{2})
@ Base ./array.jl:744
[8] collect_similar
@ ./array.jl:653 [inlined]
[9] map
@ ./abstractarray.jl:2849 [inlined]
[10] _update_min_padding!(layout::Plots.GridLayout)
@ Plots ~/.julia/packages/Plots/cPJQu/src/layouts.jl:290
[11] prepare_output(plt::Plots.Plot{Plots.GRBackend})
@ Plots ~/.julia/packages/Plots/cPJQu/src/plot.jl:224
[12] show(io::IOBuffer, m::MIME{Symbol("image/svg+xml")}, plt::Plots.Plot{Plots.GRBackend})
@ Plots ~/.julia/packages/Plots/cPJQu/src/output.jl:204
[13] sprint(::Function, ::MIME{Symbol("image/svg+xml")}, ::Vararg{Any}; context::Nothing, sizehint::Int64)
@ Base ./strings/io.jl:114
[14] sprint
@ ./strings/io.jl:108 [inlined]
[15] _ijulia_display_dict(plt::Plots.Plot{Plots.GRBackend})
@ Plots ~/.julia/packages/Plots/cPJQu/src/ijulia.jl:47
[16] display_dict(plt::Plots.Plot{Plots.GRBackend})
@ Plots ~/.julia/packages/Plots/cPJQu/src/init.jl:92
[17] #invokelatest#2
@ ./essentials.jl:716 [inlined]
[18] invokelatest
@ ./essentials.jl:714 [inlined]
[19] execute_request(socket::ZMQ.Socket, msg::IJulia.Msg)
@ IJulia ~/.julia/packages/IJulia/e8kqU/src/execute_request.jl:112
[20] #invokelatest#2
@ ./essentials.jl:716 [inlined]
[21] invokelatest
@ ./essentials.jl:714 [inlined]
[22] eventloop(socket::ZMQ.Socket)
@ IJulia ~/.julia/packages/IJulia/e8kqU/src/eventloop.jl:8
[23] (::IJulia.var"#15#18")()
@ IJulia ./task.jl:423