+---------------+          +---------------+          +---------------+
    Reference |               |   Error  |               |   Input  |               |  Output
  +----------->  Comparison   +---------->  Controller   +---------->     System    +--------->
              |               |          |               |          |               |    |
              +-------^-------+          +---------------+          +---------------+    |
                      |                                                                  |
                      |                                                                  |
                      |                                                                  |
                      |                                                                  |
                      +------------------------------------------------------------------+
                                               Feedback Path

########################
#Python program
import sys

r = float(sys.argv[1]) #Reference or "setpoint"
k = float(sys.argv[2]) #Controller gain

u = 0 #"Previous" output
for _ in range(200):
    y = u       #one-step delay: previous output
    e = r - y   #Tracking error
    u = k * e   #Controller output
    
    print r, e, 0, u, y