From: ian <ian>
Date: Mon, 27 Feb 2006 01:57:51 +0000 (+0000)
Subject: three-resistor combinations are not really that good
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ijackson/git?a=commitdiff_plain;h=1223e618e1bcc1ddcd709ed7dd3b6622a8715f95;p=trains.git

three-resistor combinations are not really that good
---

diff --git a/misc/divider-table.pl b/misc/divider-table.pl
index 4aa66e2..fbd6c6a 100755
--- a/misc/divider-table.pl
+++ b/misc/divider-table.pl
@@ -1,22 +1,11 @@
 #!/usr/bin/perl -w
 
-# for three-resistor combinations,
-# ./divider-table.pl -t |atp >ps -p -f Courier5:0.575,0,0,0.7 -B -M 18,15,15,15
-#  and then print on >=600dpi printer, preferably better
-
 use strict;
-use POSIX;
 
 our(@e12) = qw(10 12 15 18 22 27 33 39 47 56 68 82);
 our(@ex24) = qw(11 13 16 20 24 30 36 43 51 62 75 91);
 our(@e24)= sort @e12, @ex24;
 
-our (@series,$three);
-
-"@ARGV" =~ m/^(?:\-(?:t|12|24)+)?$/ or die;
-@series = "@ARGV" =~ m/12/ ? @e12 : @e24;
-$three = "@ARGV" =~ m/t/;
-
 our ($tlin,$tlog,@byrat);
 
 sub thead ($$) {
@@ -62,54 +51,32 @@ sub fracfit ($$) {
 
 sub scan () {
     my ($row,$col,$lin,$log,$rownum);
-    my ($combe,$combo,$combw,$combwe,$den,$denp);
     @byrat = ();
     thead(\$tlin,'X/Y [*10^k]');
     thead(\$tlog,'frac(L(X/Y))');
-    for $col (@series) {
+    for $col (@e24) {
 	chead(\$tlin,$col);
 	chead(\$tlog,$col);
     }
     theadend(\$tlin);
     theadend(\$tlog);
     $rownum= 0;
-    for $row (@series) {
+    for $row (@e24) {
 	rhead(\$tlin,$row);
 	rhead(\$tlog,$row);
-	for $col (@series) {
-	    for $combo (('', '|', '+')) {
-		next if length($combo) and not $three;
-		for $combw (length($combo) ? @series : ('')) {
-		    for $combe (length($combo) ? (0, 1, 2) : (0,)) {
-			if ($combo eq '') {
-			    $den= $denp= $row;
-			} else {
-			    $combwe= $combw * pow(10, -2 + $combe);
-			    $den= $combo eq '+' ? $row + $combwe :
-				1.0/(1.0/$row + 1.0/$combwe);
-			    $denp= $combw;
-			    $denp =~ s/.{$combe}/$&\./;
-			    $denp= $row.$combo.$denp;
-			    next if grep {
-				abs(fmod(abs(log($_/$den)) + 0.1,
-					 log(10)) - 0.1) < 1e-6
-				} @series;
-			}
-			$lin= $col*1.0 / $den;
-			while ($lin < 1000) { $lin *= 10; }
-			$log= log($lin)/log(10) + 1.0;
-
-			cell(\$tlin, mul10fit($lin,5));
-			cell(\$tlog, fracfit($log,5));
-
-			next if $row==$col;
-			push @byrat, { Num => $col,
-				       Den => $denp,
-				       Lin => $lin,
-				       Log => $log };
-		    }
-		}
-	    }
+	for $col (@e24) {
+	    $lin= $col*1.0 / $row;
+	    $log= log($lin)/log(10) + 1.0;
+
+	    cell(\$tlin, mul10fit($lin,5));
+	    cell(\$tlog, fracfit($log,5));
+
+	    if ($col < $row) { $lin *= 10; }
+	    next if $row==$col;
+	    push @byrat, { Num => $col,
+			   Den => $row,
+			   Lin => $lin,
+			   Log => $log };
 	}
 	rend(\$tlin,$rownum);
 	rend(\$tlog,$rownum);
@@ -130,24 +97,10 @@ sub ptable ($) {
 
 sub sortbyrat () {
     @byrat= sort {
-	$a->{Lin} <=> $b->{Lin} or
-	$a->{Num} <=> $b->{Num}
+	$a->{Lin} <=> $b->{Lin}
     } @byrat;
 }
 
-sub uniqbyrat () {
-    my ($last,$i,$t,@byratnew);
-    @byratnew= ();
-    $last= 'x';
-    for $i (@byrat) {
-	$t= "$i->{Num} $i->{Lin}";
-	next if $t eq $last;
-	push @byratnew, $i;
-	$last= $t;
-    }
-    @byrat= @byratnew;
-}
-
 sub byratcol ($$$) {
     my ($or,$cwr,$colnum) = @_;
     $$or .= '  ' if $colnum;
@@ -156,21 +109,19 @@ sub byratcol ($$$) {
 
 sub printbyrat () {
     use integer;
-    my ($brcols) = $three ? 19 : 8;
+    my ($brcols) = 8;
     my ($brrows) = (@byrat+$brcols-1) / $brcols;
     my ($byrat,$o,$colnum,$rownum,$cw);
     $o= ''; 
     for ($colnum=0; $colnum<$brcols; $colnum++) {
 	byratcol(\$o,\$cw,$colnum);
-	$o .= sprintf("N:D%s %".($cw+1)."s",
-		      $three ? '[&X]' : '',
-		      'Q*10^k');
-	$o .= sprintf(" %s", $three ? '' : 'fc(Lg)');
+	$o .= sprintf("N/D %".($cw+1)."s %s",
+		      'Q*10^k','fc(Lg)');
     }
     $o .= "\n";
     for ($colnum=0; $colnum<$brcols; $colnum++) {
 	byratcol(\$o,\$cw,$colnum);
-	$o .= '-' x (5+1+$cw+($three ? 4 : 1+5));
+	$o .= '-' x (5+1+$cw+1+5);
     }
     $o .= "\n";
     for ($rownum=0; $rownum<$brrows; $rownum++) { 
@@ -178,10 +129,10 @@ sub printbyrat () {
 	    $byrat= $byrat[$colnum*$brrows + $rownum];
 	    next unless defined $byrat;
 	    byratcol(\$o,\$cw,$colnum);
-	    $o .= sprintf("%2s:%-".($three ? 6 : 2)."s %${cw}s",
+	    $o .= sprintf("%2s/%-2s %${cw}s %s",
 			  $byrat->{Num}, $byrat->{Den},
-			  mul10fit($byrat->{Lin}, $cw));
-	    $o .= sprintf(" %s", fracfit($byrat->{Log}, 5)) unless $three;
+			  mul10fit($byrat->{Lin}, $cw),
+			  fracfit($byrat->{Log}, 5));
 	}
 	$o .= "\n";
     }
@@ -190,11 +141,8 @@ sub printbyrat () {
 
 print "\n" or die $!;
 scan();
-if (!$three) {
-    ptable($tlin);
-    ptable($tlog);
-}
+ptable($tlin);
+ptable($tlog);
 
 sortbyrat();
-uniqbyrat() if $three;
 printbyrat();