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1 files changed, 45 insertions, 0 deletions

diff --git a/parallel_resistors b/parallel_resistors
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+++ b/parallel_resistors
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+#!/usr/bin/perl -w
+
+if(@ARGV < 2) {
+	usage();
+	exit 0;
+}
+
+for(@ARGV) {
+	if(/^([\d.]+)k/i) {
+		$_ = $1 * 1000;
+	} elsif(/^([\d.]+)m/i) {
+		$_ = $1 * 1000000;
+	}
+
+	if(not $_+0) {
+		warn "Invalid resistance: $_\n";
+		usage();
+		exit 1;
+	}
+}
+
+$res += 1/$_ for @ARGV;
+printf "%.2f\n", 1/$res;
+#print 1/$res, "\n";
+
+sub usage {
+	my $b = $0;
+	$b =~ s/.*\///;
+	print <<EOF;
+Usage: $b r1 r2 [r3] [r4] [...]
+
+Calculates the total resistance of two or more resistances in parallel,
+according to the formula:
+
+1 / ( (1/r1) + (1/r2) + ... + (1/rN) )
+
+Resistance values can contain a decimal point, and may be given in ohms
+(with no suffix, e.g. 100, 470, 10000), or in units of 1000 ohms (suffix
+"K" or "k": 1K, 4.7k, 0.1k), or units of 1 million ohms (suffix "M" or
+"m": 1M, 4.7m, 0.1m).
+
+Result is always given in ohms.
+
+EOF
+}