Index: mttroot/mtt/lib/cr/r/slin.cr
==================================================================
--- mttroot/mtt/lib/cr/r/slin.cr
+++ mttroot/mtt/lib/cr/r/slin.cr
@@ -1,9 +1,32 @@
 %DESCRIPTION Sensitivity version of lin
 
+% One port version for historical reasons
 OPERATOR slin;
 FOR ALL gain_causality, gain, causality, input, other_causality
 LET slin(gain_causality, gain, other_causality, 1, input, causality, 1)
          = lin(gain_causality, gain, other_causality, 1, input,
 	 causality, 1);
+
+% Two port version for sC,sI,sR 
+
+% Port 1 - standard 
+FOR ALL gain_causality, gain, sgain, causality, input, sinput, other_causality
+LET slin(gain_causality, gain, sgain, other_causality, 1, 
+       input, causality, 1,
+       sinput, causality, 2)
+         = lin(gain_causality, gain, other_causality, 1, 
+               input, causality, 1); 
+
+
+% Port 2 - sensitivity
+FOR ALL gain_causality, gain, sgain, causality, input, sinput, other_causality
+LET slin(gain_causality, gain, sgain, other_causality, 2, 
+       input, causality, 1,
+       sinput, causality, 2)
+         = lin(gain_causality, gain, other_causality, 1, 
+               sinput, causality, 1)
+         + sgain*df(lin(gain_causality, gain, other_causality, 1, 
+               input, causality, 1), gain); 
+
 END;;