julia programming language

Learn from examples

1. Program to output a string, integer,  and floating point

  exjl1.jl source code


# exjl1.jl  various ways to print string, integer, float or double
using Printf    # only needed for @printf

println("julia exjl1.jl running")
print("julia exjl1")
print(".jl")
print(" running")
println(" multiple print on one line")

cstr = "a string"
@printf "cstr = %s \n" cstr

bint = 9999
print("bint = ")
print(bint)
println(" ")
	
@printf "bint = %d \n" bint

aflt = 1.5
print("aflt = ")
print(aflt)
println(" ")
	
@printf "aflt = %7.4f \n" aflt

bigflt = 123456789.987654321e+249
@printf "bigflt = %22.18e \n" bigflt

println(1.5, " ", 2, " abc")
println(" ")

println("exjl1.jl finished")
# end exjl1.jl


  Output from execution:

julia exjl1.jl running
julia exjl1.jl running multiple print on one line
cstr = a string 
bint = 9999 
bint = 9999 
aflt = 1.5 
aflt =  1.5000 
bigflt = 1.234567899876543095e+257 
1.5 2 abc
 
exjl1.jl finished



2. commands to execute the source code
   at a minimum, Windows, Linux, MacOSX.

   Windows: 
     julia exjl1.jl     
  
   Linux:
     julia exjl1.jl

   MacOSX
     julia exjl1.jl


3. You must be able to declare variables and arrays
   and matrix of various types.

  exjl3.jl source code

# exjl3.jl  declare and print variable, vector, matrix
using Printf  # only needed if  @printf  will be used

println("julia exjl3.jl running")

s1 = "any string"
println(s1)
s2 = "more"
println(s2)
s3 = s1*s2  # concatenation
println(s3)
s4 = s1*" "*s2  # space between strings
println(s4)

i = 13         # integer  Int
print("i = ")
print(i)       # print can print everything, even arrays
println(" ")   # no line feed in just  print
@printf "i = %d \n" i   # "C" format and list

x = 0.0        # double  Float64
@printf "x=%f \n" x
for i in 1:4
  global x
  x = x + 1.0
end
@printf "x=%f \n" x


v1 = [ 1 2 3 4 ]  # row vector  no comma
print("v1=")
print(v1)
print("  row vector");
println(" ")
@printf "v1[3]=%d \n" v1[3]

v2 = [1, 2, 3, 4]  # typical row vector
print("v2=")
print(v2)
print("  with ,  row vector");
println(" ")
@printf "v2[3]=%d \n" v2[3]

v3 = [ 1 2 3 4 ]' # column vector "'"
print("v3=")
print(v3)
print("  with '  column vector");
println(" ")
@printf "v3[3]=%d \n" v3[3]

# matrix
A = Array{Float64,2}(undef, 2, 3)
println("A created ")
print("A=")
print(A)
println(" ")

A0 = zeros(2, 3)
print("A0=")
print(A0)
println(" ")

A1 = ones(2, 3)
print("A1=")
print(A1)
println(" ")

B = [1.0 2.0 3.0 ; 4.0 5.0 6.0] # no commas!  ; or new line
print("B=")
print(B)
println(" ")

nrow = size(B,1)
print("nrow=size(B,1)=")
println(nrow)
ncol = size(B,2)
print("ncol=size(B,2)=")
println(ncol)
println(" ")

println("exjl3.jl finished")
# end exjl3.jl


Execution output:

julia exjl3.jl running
any string
more
any stringmore
any string more
i = 13 
i = 13 
x=0.000000 
x=4.000000 
v1=[1 2 3 4]  row vector 
v1[3]=3 
v2=[1, 2, 3, 4]  with ,  row vector 
v2[3]=3 
v3=[1; 2; 3; 4]  with '  column vector 
v3[3]=3 
A created 
A=[4.24399e-314 3.31031e-312 -1.10215e213; 3.22543e-312 3.35275e-312 2.3178e-313] 
A0=[0.0 0.0 0.0; 0.0 0.0 0.0] 
A1=[1.0 1.0 1.0; 1.0 1.0 1.0] 
B=[1.0 2.0 3.0; 4.0 5.0 6.0] 
nrow=size(B,1)=2
ncol=size(B,2)=3
 
exjl3.jl finished


4. You need to be able to have loops, iteration statements

  exjl4.jl source code

# exjl4.jl  example loops and iteration
using Printf

println("julia exjl4.jl running")

for i in 1:5
    print(i, ", ")
end
println() # 1, 2, 3, 4, 5, 

for i = 1:5       # both "in" and "=" work
    print(i, ", ")
end
println() # 1, 2, 3, 4, 5, 

arr = [2,4,6,8]
for i in 1:4  # array index starts at 1 like Fortran, Matlab
    print(i, ", ")
end
println() # 2, 4, 6, 8 


# arrays can also be looped over directly:
a1 = [2,4,6,8]
for i in a1
    print(i, ", ")
end
println() # 2, 4, 6, 8, 

# continue and break work in loops
a2 = collect(1:20)
for i in a2
    if i % 2 != 0
        continue
    end
    print(i, ", ")
    if i >= 8
        break
    end
end
println() # 2, 4, 6, 8, 


d1 = Dict(1=>"one", 2=>"two", 3=>"three")
# dicts may be looped through using the keys function:
for k in sort(collect(keys(d1)))
    print(k, ": ", d1[k], ", ")
end
println() # 1: one, 2: two, 3: three,

# enumerate can be used to get both the index and value in a loop
a3 = ["one", "two", "three"]
for (i, v) in enumerate(a3)
    print(i, ": ", v, ", ")
end
println() # 1: one, 2: two, 3: three, 


# map works as you might expect performing the given function on each member of an array or iter much like comprehensions
a4 = map((x) -> x^2, [1, 2, 3, 7])
print(a4) # 4-element Array{Int64,1}: [1,4,9,49]
println(" ")

println("exjl4.jl finished")
# end exjl4.jl


Execution output:

julia exjl4.jl running
1, 2, 3, 4, 5, 
1, 2, 3, 4, 5, 
1, 2, 3, 4, 
2, 4, 6, 8, 
2, 4, 6, 8, 
1: one, 2: two, 3: three, 
1: one, 2: two, 3: three, 
[1, 4, 9, 49] 

exjl4.jl finished




5. You need  if then else  conditional statements

  exjl5.jl source code

# exjl5.jl  example  if then else
using Printf

println("julia exjl5.jl running")
# <  >  <=  >=  ==  !=   &&  ||
function test(x, y)
  if x < y
     println("x is less than y")
  elseif x > y
     println("x is greater than y")
  elseif x <= y  ||  x != y
     println("x is greater than y")
  elseif x >= y  &&  x == Y
     println("x is greater than y")
  elseif x == y
     println("x is greater than y")
  elseif x != y
     println("x is greater than y")
  else
     println("x is equal to y")
  end
end

test(1, 2)

test(2, 1)

test(1, 1)

println("exjl5.jl finished")
# end exjl5.jl


	  
Execution output:


julia exjl5.jl running
x is less than y
x is greater than y
x is greater than y
exjl5.jl finished



6. You need to be able to create functions, procedures,
   subroutines.

  exjl6.jl source code

# exjl6.jl  example create and use functions and procedures
using Printf

function anyarg(a1, a2, a3, a4) # procedure  because  return nothing
  print("a1 = ")
  print(a1)
  println(" ")
  print("a2 = ")
  print(a2)
  println(" ")
  print("a3 = ")
  print(a3)
  println(" ")
  print("a4 = ")
  print(a4)
  println(" ")
  return nothing
end # anyarg

function mulany(A, B) # A and B of some type
  C = A*B
  return C
end # mulany

function targs(A::String, B::Float64, C::Int)
  println("targs A = "*A)
  @printf "B = %f \n" B
  @printf "C = %d \n" C
  return nothing
end # targs

println("julia exjl6.jl running") # functions before first executable
i = 13
s1 = "my string"
x = 3.5
M1 = [ 1.0 2.0; 3.0 4.0 ]
M2 = Array{Float64, 2}(undef,2,2)
M2[1,1] = 1.1
M2[1,2] = 2.2
M2[2,1] = 3.3
M2[2,2] = 4.4

println("anyarg, no type checking")
anyarg(i, s1, x, M1)
println(" ")

anyarg(M1, x, i, s1) # with no type checking
println(" ")

Q = mulany(i, 2)
print("Q = mulany(i, 2) =")
print(Q)
println(" ")

Q = mulany(s1, "more")
print("Q = mulany(s1, more ) =")
print(Q)
println(" ")

Q = mulany(x, 2.0)
print("Q = mulany(x, 2.0) =")
print(Q)
println(" ")

Q = mulany(M1, M2)
print("Q = mulany(M1, M2) =")
print(Q)
println(" ")
println(" ")

targs(s1, x, i) # must agree with type
println(" ")

println("exjl6.jl finished")
# end exjl6.jl


Execution output:

julia exjl6.jl running
anyarg, no type checking
a1 = 13 
a2 = my string 
a3 = 3.5 
a4 = [1.0 2.0; 3.0 4.0] 
 
a1 = [1.0 2.0; 3.0 4.0] 
a2 = 3.5 
a3 = 13 
a4 = my string 
 
Q = mulany(i, 2) =26 
Q = mulany(s1, more ) =my stringmore 
Q = mulany(x, 2.0) =7.0 
Q = mulany(M1, M2) =[7.7 11.0; 16.5 24.2] 
 
targs A = my string
B = 3.500000 
C = 13 
 
exjl6.jl finished
  

7. You need to be able to read and write files in various formats.

  exjl7.jl source code

# exjl7.jl  example read and write files
using Printf

println("julia exjl7.jl running")

println("open txt_jl.dat for writing")

fout = open("txt_jl.dat","w")
println(fout, "line 1")
println(fout, "line 2")
println(fout, "last line")
close(fout)

println("file  txt_jl.dat  written")
println(" ")
println("open txt_jl.dat for reading")

open("txt_jl.dat") do f
  for ln in eachline(f)
    print("line= ")
    println(ln)
  end
end

println("read and printed  txt_jl.dat")

println("convert string to Float64 or Int")
x = parse(Float64,"13.54")
@printf "x= %f \n" x
i = parse(Int,"135")
@printf "i= %d \n" i

println("convert Float64 and Int to string")
x = 13.54;
xstr = @sprintf("%f",x)
@printf "xstr = %s \n" xstr
i = 135
istr = @sprintf("%d",i)
@printf "istr = %s \n" istr

s="1.0 2.5 3.7 4.5"
print("s=")
println(s)
sv = split(s)
print("split(s)=")
println(sv)
n=size(sv,1)
print("n=size(sv,1)=")
println(n)
@printf "n=%s \n" n

for k in 1:n
  println(sv[k])
end

print("sv[1]=")
println(sv[1])
print("sv[2]=")
println(sv[2])
print("sv[3]=")
println(sv[3])
print("sv[4]=")
println(sv[4])

print("sv[1]*sv[2]*sv[3]*sv[4]=")
println(sv[1]*sv[2]*sv[3]*sv[4])
print("sv[1]*space*sv[2]*space*sv[3]*space*sv[4]=")
svs = sv[1]*" "*sv[2]*" "*sv[3]*" "*sv[4]
println(svs)

println("exjl7.jl finished")
# end exjl7.jl


Execution output:

julia exjl7.jl running
open txt_jl.dat for writing
file  txt_jl.dat  written
 
open txt_jl.dat for reading
line= line 1
line= line 2
line= last line
read and printed  txt_jl.dat
convert string to Float64 or Int
x= 13.540000 
i= 135 
convert Float64 and Int to string
xstr = 13.540000 
istr = 135 
s=1.0 2.5 3.7 4.5
split(s)=SubString{String}["1.0", "2.5", "3.7", "4.5"]
n=size(sv,1)=4
n=4 
1.0
2.5
3.7
4.5
sv[1]=1.0
sv[2]=2.5
sv[3]=3.7
sv[4]=4.5
sv[1]*sv[2]*sv[3]*sv[4]=1.02.53.74.5
sv[1]*space*sv[2]*space*sv[3]*space*sv[4]=1.0 2.5 3.7 4.5
exjl7.jl finished


8. You need to be able to use a number of files combined to
   build a program. This may include packages, libraries,
   operating system commands, header files, etc.

  exjl8.jl source code

  ???

Execution output:

 ???
  
9. extra examples: math, complex, matrix function, numerical integration,
  numerical derivatives, partial differential equations

math_funct.jl source code
math_funct_jl.out output

test_complex.jl source code
test_complex_jl.out output

matrix.jl source code
matrix_jl.out output

test_gaulegf.jl source code
test_gaulegf_jl.out output

test_nuderiv.jl source code
test_nuderiv_jl.out output

pde22_eq.jl source code
pde22_eq_jl.out output
pde22_eq_jl.dat data output
pde22_eq_jl.sh run plot
pde22_eq_jl.plot plot data
pde22_eq_jl.png output