From 57810dc9b1ff8993050bc5e19474d915d47d0d6e Mon Sep 17 00:00:00 2001
From: e78783 <fungcheokyin@gmail.com>
Date: Tue, 17 May 2022 20:41:27 +0800
Subject: blogpost, julia soln, edit ch-2.pl

---
 challenge-165/cheok-yin-fung/blog.txt      |  1 +
 challenge-165/cheok-yin-fung/julia/ch-2.jl | 81 ++++++++++++++++++++++++++++++
 challenge-165/cheok-yin-fung/perl/ch-2.pl  |  9 ++--
 3 files changed, 86 insertions(+), 5 deletions(-)
 create mode 100644 challenge-165/cheok-yin-fung/blog.txt
 create mode 100644 challenge-165/cheok-yin-fung/julia/ch-2.jl

diff --git a/challenge-165/cheok-yin-fung/blog.txt b/challenge-165/cheok-yin-fung/blog.txt
new file mode 100644
index 0000000000..b5566b2f41
--- /dev/null
+++ b/challenge-165/cheok-yin-fung/blog.txt
@@ -0,0 +1 @@
+https://e7-87-83.github.io/coding/challenge_165.html
diff --git a/challenge-165/cheok-yin-fung/julia/ch-2.jl b/challenge-165/cheok-yin-fung/julia/ch-2.jl
new file mode 100644
index 0000000000..bd0113f50d
--- /dev/null
+++ b/challenge-165/cheok-yin-fung/julia/ch-2.jl
@@ -0,0 +1,81 @@
+#!/usr/bin/perl
+# The Weekly Challenge 165
+# Task 2 Line of Best Fit
+# Julia Solution
+# ref:
+# https://jahoo.github.io/2021/01/11/simplest_linear_regression_example.html
+
+
+using Plots
+
+data = [
+333,129 ,
+39,189 ,
+140,156 ,
+292,134 ,
+393,52 ,
+160,166 ,
+362,122 ,
+13,193 ,
+341,104 ,
+320,113 ,
+109,177 ,
+203,152 ,
+343,100 ,
+225,110 ,
+23,186 ,
+282,102 ,
+284,98 ,
+205,133 ,
+297,114 ,
+292,126 ,
+339,112 ,
+327,79 ,
+253,136 ,
+61,169 ,
+128,176 ,
+346,72 ,
+316,103 ,
+124,162 ,
+65,181 ,
+159,137 ,
+212,116 ,
+337,86 ,
+215,136 ,
+153,137 ,
+390,104 ,
+100,180 ,
+76,188 ,
+77,181 ,
+69,195 ,
+92,186 ,
+275,96 ,
+250,147 ,
+34,174 ,
+213,134 ,
+186,129 ,
+189,154 ,
+361,82 ,
+363,89 ,
+]
+
+xs = []
+ys = []
+
+for i = 1:2:length(data)-1
+    push!(xs,data[i])
+end
+
+for i = 2:2:length(data)
+    push!(ys,data[i])
+end
+
+scatter(xs, ys)
+
+A = convert(Matrix{Float64}, hcat(xs, ones(length(xs))))
+
+slope, intercept = inv(transpose(A)*A)*transpose(A) * ys
+
+plot!(x -> slope*x + intercept, legend = :none)
+
+savefig("new_julia.svg")
diff --git a/challenge-165/cheok-yin-fung/perl/ch-2.pl b/challenge-165/cheok-yin-fung/perl/ch-2.pl
index 4cc8f19c0a..7d0c7fb658 100644
--- a/challenge-165/cheok-yin-fung/perl/ch-2.pl
+++ b/challenge-165/cheok-yin-fung/perl/ch-2.pl
@@ -19,18 +19,17 @@ while (<>) {
 my $n = scalar @points;
 
 my $slope = 
-     (  $n * sum(map {$_->[0]*$_->[1]} @points)
-      - sum(map{$_->[0]} @points) * sum(map{$_->[1]} @points) )
-    / ( $n * sum(map{$_->[0]**2} @points)
+     (  $n * sum(map {$_->[0]*$_->[1]} @points)  # n sum(xy) - sum(x) sum(y)
+      - sum(map{$_->[0]} @points) * sum(map{$_->[1]} @points) ) 
+    / ( $n * sum(map{$_->[0]**2} @points)        # n sum(sq x) - sq(sum x)
          - (sum( map { $_->[0]} @points ))**2) ;
 
 
 my $intercept =
-     ( sum( map {$_->[1]} @points ) 
+     ( sum( map {$_->[1]} @points )             # sum(y) - slope * sum(x)
     - $slope * sum( map {$_->[0]} @points) )
     / $n ;
 
-
 sub y_best_fit {
     my $x = $_[0];
     return $slope*$x + $intercept;
-- 
cgit