did this week's challenges, both trivial

3 files changed, 114 insertions, 11 deletions

diff --git a/challenge-011/duncan-c-white/README b/challenge-011/duncan-c-white/README
index fb3a863c80..3ff28fa716 100644
--- a/challenge-011/duncan-c-white/README
+++ b/challenge-011/duncan-c-white/README
@@ -1,14 +1,24 @@
-Challenge 1: "Create a script which takes a list of numbers from
-command line and print the same in the compact form. For example, if
-you pass 1,2,3,4,9,10,14,15,16 then it should print the compact form
-like 1-4,9,10,14-16.."
+Challenge 1: "Write a script that computes the equal point in the Fahrenheit and Celsius scales, knowing that the freezing point of water is 32 °F and 0 °C, and that the boiling point of water is 212 °F and 100 Â,"
 
-Quite simple and dull problem. But ok, let's have a go.
+My notes: Isn't that just Maths?  solve F = 9/5C + 32 for F==C?
 
-Challenge 2: "Create a script to calculate Ramanujan's constant with at
-least 32 digits of precision."
+C = 9/5C + 32 => 4/5C = -32 => C = 5/4 x -32 = 5 x -8 = -40
 
-Never heard of this constant, seems to be e^(pi*sqrt(163)), which is
-"very nearly an integer", I don't particularly care about abtruse mathematical
-formulae.  But ok, Perl's built in module biggrat will let you do this anyway,
-specifying accuracy 32; see ch-2.sh for the oneliner.
+But if I have to "compute" something that I should obviously "solve by
+algebra", could I do some sort of "where do two lines intersect" solver?
+Let's have a go.
+
+
+Challenge 2: "Write a script to create an Indentity Matrix for the given
+size. For example, if the size is 4, then create Identity Matrix 4x4."
+
+My notes:
+
+Surely that's incredibly straight forward.  The identity matrix has 1s
+on the leading diagonal and 0s everywhere else.  But should we create
+it in memory as a 2-D array and print that out, or just print out the
+identity matrix?  Let's choose the latter as it's simpler and more direct,
+even though the former approach would be more useful in real life, as
+presumably this is going to be one operation in a more general Matrix
+class/module [really, these questions need to be BETTER SPECIFIED to
+clarify this sort of thing]
diff --git a/challenge-011/duncan-c-white/perl5/ch-1.pl b/challenge-011/duncan-c-white/perl5/ch-1.pl
new file mode 100755
index 0000000000..8597a87110
--- /dev/null
+++ b/challenge-011/duncan-c-white/perl5/ch-1.pl
@@ -0,0 +1,62 @@
+#!/usr/bin/perl
+
+# Challenge 1: "Write a script that computes the equal point in the
+# Fahrenheit and Celsius scales, knowing that the freezing point of water
+# is 32 °F and 0 °C, and that the boiling point of water is 212 °F and
+# 100."
+#
+# My notes: Isn't that just Maths?  solve F = 9/5C + 32 for F==C?
+# 
+# C = 9/5C + 32 => 4/5C = -32 => C = 5/4 x -32 = 5 x -8 = -40
+# 
+# But if I have to "compute" something that I should obviously "solve by
+# algebra", could I do some sort of "where do two lines intersect" solver?
+# Let's have a go.
+
+
+use strict;
+use warnings;
+use Function::Parameters;
+use Data::Dumper;
+
+my $c = 0;
+my $delta = 3.0;
+my $epsilon = 0.000001;
+
+#
+# my $f = fahr($c);
+#	Convert celsius $c to fahrenheit $f.
+#
+fun fahr( $c )
+{
+	return 9.0*$c/5.0 + 32;
+}
+
+#
+# my $error = offby( $c );
+#	Compute and return "how far is fahr(c) off by (different from c)"
+#
+fun offby( $c )
+{
+	return abs(fahr($c)-$c);
+}
+
+
+#die "c=0, f=", fahr(0), "\nc=100, f=", fahr(100), "\n";
+
+# compute the intersection point of F = 9/5C + 32 and C = 5/9(F-32),
+# ie. the value of c for which F(c)==c,
+# using the fact that | F(c)-c | diminishes monotonically as we get
+# closer to the solution value of c
+# 
+do {
+	my $sd = ( offby($c-$delta) < offby($c) ) ?  -$delta : $delta;
+	while( offby($c+$sd) < offby($c) )
+	{
+		$c += $sd;
+	}
+	print "c=$c, diff=", offby($c), ", delta=$delta\n";
+	$delta /= 10.0;
+} while( abs( fahr($c)-$c ) > $epsilon );
+
+print "c=$c\n";
diff --git a/challenge-011/duncan-c-white/perl5/ch-2.pl b/challenge-011/duncan-c-white/perl5/ch-2.pl
new file mode 100755
index 0000000000..2662e3b6d6
--- /dev/null
+++ b/challenge-011/duncan-c-white/perl5/ch-2.pl
@@ -0,0 +1,31 @@
+#!/usr/bin/perl
+
+# Challenge 2: "Write a script to create an Indentity Matrix for the given
+# size. For example, if the size is 4, then create Identity Matrix 4x4."
+# 
+# My notes:
+# 
+# Surely that's incredibly straight forward.  The identity matrix has 1s on the
+# leading diagonal and 0s everywhere else.  But should we create it in memory
+# as a 2-D array and print that out, or just print out the identity matrix?
+# Let's choose the latter as it's simpler and more direct, even though the
+# former approach would be more useful in real life, as presumably this is
+# going to be one operation in a Matrix class/module [really, these questions
+# need to be BETTER SPECIFIED to clarify this sort of thing]
+
+die "Usage: ch-2.pl N\n" unless @ARGV == 1;
+
+my $n = shift;
+
+die "ch-2.pl: n ($n) must be > 0\n" unless $n>0;
+
+for( $row=0; $row<$n; $row++ )
+{
+	my $line ='';
+	for( $col=0; $col<$n; $col++ )
+	{
+		my $ch = ($row==$col)?'1':'0';
+		$line .= $ch;
+	}
+	print "$line\n";
+}