ADDED   mttroot/mtt/lib/cr/perl/Density.pm
Index: mttroot/mtt/lib/cr/perl/Density.pm
==================================================================
--- /dev/null
+++ mttroot/mtt/lib/cr/perl/Density.pm
@@ -0,0 +1,156 @@
+#-------------------------------------------------------------------------------
+#			Model Transformation Tools
+#-------------------------------------------------------------------------------
+
+
+package Density;
+
+#-------------------------------------------------------------------------------
+#		linear constitutive relationship with cosine modulation
+#-------------------------------------------------------------------------------
+
+use strict;
+use warnings;
+
+#-------------------------------------------------------------------------------
+# standard module header (see perlmod for explanation)
+#-------------------------------------------------------------------------------
+BEGIN {
+    use Exporter   ();
+    our ($VERSION, @ISA, @EXPORT, @EXPORT_OK, %EXPORT_TAGS);
+
+    $VERSION     = 1.00;
+
+    @ISA         = qw(Exporter);
+    @EXPORT      = qw(&Density);	# CR name
+    %EXPORT_TAGS = ( );
+}
+
+#-------------------------------------------------------------------------------
+# declaration of specific component implementations
+#-------------------------------------------------------------------------------
+sub Density_r(@);		# R
+
+#-------------------------------------------------------------------------------
+# main function: selects which subfunction to call
+#-------------------------------------------------------------------------------
+sub Density (@) {
+
+    my $retval;
+
+    $_ = $_[0];
+
+    s/\((.*)\)/$1/;		# strip brackets
+    my @args = split (/,/);	# split arguments
+
+    $_ = $args[0];		# get component type
+
+    # select rule to use
+    if (/^R|r$/)	{ $retval = Density_r	(@args); }
+    
+    # if a substitution has been made ($retval)
+    if ($retval)
+    {
+	return $retval;		# return substituted expression
+    }
+    else			# return nothing
+    {
+	return;
+    }
+}
+
+#-------------------------------------------------------------------------------
+# R
+#-------------------------------------------------------------------------------
+sub Density_r (@) {
+
+    my @args = @_;
+    my $retval = '';
+    
+    if ($#args == 15-1)
+    {
+	if ($args[2] eq 'ideal_gas')
+	{
+	    my ($component,
+		$required_output,
+		$law,
+		$R,
+		$out_causality,
+		$out_port,
+		$Pressure,
+		$P_causality,
+		$P_port,
+		$Temperature,
+		$T_causality,
+		$T_port,
+		$Nothing,
+		$N_causality,
+		$N_port) = @args;
+	    
+	    if (($P_causality eq 'effort') and
+		($P_port == 1) and
+		($T_causality eq 'effort') and
+		($T_port == 2) and
+		($N_causality eq 'flow') and
+		($N_port == 3))
+	    {
+		if ($required_output eq 'density')
+		{
+		    return "(($Pressure)/(($R)*($Temperature)))";
+		}
+		elsif ($required_output eq 'specific_volume')
+		{
+		    return "(($R)*($Temperature)/($Pressure))";
+		}
+	    }
+	}
+	elsif ($args[2] eq 'incompressible')
+	{
+	    my ($component,
+		$required_output,
+		$law,
+		$rho,
+		$out_causality,
+		$out_port,
+		$Pressure,
+		$P_causality,
+		$P_port,
+		$Temperature,
+		$T_causality,
+		$T_port,
+		$Nothing,
+		$N_causality,
+		$N_port) = @args;
+	    
+	    if (($P_causality eq 'effort') and
+		($P_port == 1) and
+		($T_causality eq 'effort') and
+		($T_port == 2) and
+		($N_causality eq 'flow') and
+		($N_port == 3))
+	    {
+		if ($required_output eq 'density')
+		{
+		    return "($rho)";
+		}
+		elsif ($required_output eq 'specific_volume')
+		{
+		    return "(1/($rho))";
+		}
+	    }
+	}
+    }
+    
+    if ($retval)
+    {
+	return $retval;
+    }
+    else
+    {
+	return;
+    }
+}
+
+#-------------------------------------------------------------------------------
+1;				# return true
+