ADDED   mttroot/mtt/lib/cr/r/polytrop.cr
Index: mttroot/mtt/lib/cr/r/polytrop.cr
==================================================================
--- /dev/null
+++ mttroot/mtt/lib/cr/r/polytrop.cr
@@ -0,0 +1,42 @@
+%SUMMARY polytrop	CR for gas turbine compressor
+
+
+OPERATOR polytrop;
+
+% Port 1 generates zero flow
+FOR ALL deltaP,temperature,pressure,k,deltaT
+LET polytrop(k, flow, 1,
+		deltaP,effort,1,
+		deltaT,effort,2,
+		temperature,effort,3,
+		pressure,effort,4)
+	 = 0;
+
+% Port 2 generates deltaT
+FOR ALL deltaP,temperature,pressure,k,deltaT
+LET polytrop(k, effort, 2,
+		deltaP,effort,1,
+		deltaT,effort,2,
+		temperature,effort,3,
+		pressure,effort,4)
+	 = temperature*((1-(deltaP/pressure)^((k-1)/k)-1);
+
+% Port 3 generates zero flow
+FOR ALL deltaP,temperature,pressure,k,deltaT
+LET polytrop(k, flow, 3,
+		deltaP,effort,1,
+		deltaT,effort,2,
+		temperature,effort,3,
+		pressure,effort,4)
+	 = 0;
+
+% Port 4 generates zero flow
+FOR ALL deltaP,temperature,pressure,k,deltaT
+LET polytrop(k, flow, 4,
+		deltaP,effort,1,
+		deltaT,effort,2,
+		temperature,effort,3,
+		pressure,effort,4)
+	 = 0;
+
+