From: utzoo!decvax!cca!fortune!rpw3@sri-unix Newsgroups: net.jokes.d,net.math Title: History/Explanation of Polish Airliner Joke (**Spoiler**) Article-I.D.: fortune.92 Posted: Mon Jun 28 02:45:27 1982 Received: Tue Jun 29 05:49:58 1982 The following facts, as requested: The "Polish Airliner Joke" (recently put to net.jokes) was first heard (by me) at a San Diego or Anaheim DECUS meeting about 8-9 years ago. I believe it was invented by Ashley Grayson, who was a DEC edu-sales person at the time. ******SPOILER****** ******SPOILER****** ******SPOILER****** For non-engineers: The "poles" referred to are the values of complex frequency in the s-transform or z-transform equations of input/output for which the denominator of the equation [usually a rational polynomial in e^(i*omega*t)] goes to zero, causing the output to go to "infinity" ==> **CRASH**. The "plane" is the plot of complex frequencies: -x/+x is exponentially decreasing/increasing amplitude of response; +/- y is real frequency. For values of a driving function on the "right half" (i.e., +x), the input (and presumably the output) in exponentially increasing. If all of the poles are on the right half, the system can do it to itself (to destruction) without any input (other than a miniscule bit of noise to get it oscillating). Enough?