Reverse Polish Notation and The Stack - Computerphile

Reverse Polish, or Postfix notation is commonly used in Computer Science, particularly in reference to Stacks - but what are stacks and how does postfix work? Professor David Brailsford takes us through it.

This video was filmed and edited by Sean Riley.

[duckrutt]

The best part about having a RPN calculator is it will only be borrowed by anyone once and you will always get it back.

[Jarzyniak]

As a Pole, I'm incredibly impressed by his pronunciation of Łukasiewicz's name.

[tomasznikiel]

Perfect spelling of the Polish name, respect for digging it up.

[thesnowedone]

The key thing to remember here is that not only is this efficient processor wise; RPN is also efficient memory wise.  You don't have to keep track of multiple variables all over the place; everything you need to complete your operations is in the stack in the order you are going to have to process them.

It's a very tidy system and a core component of computing that is normally hidden by higher level languages.

[vagramAU]

Wish i had such a passionate professor at uni, good stuff.

[mikelipsey]

It's very refreshing having a gentleman this age teaching these with this passion!  Great teacher!  Thank you, sir.

[jamestaylor]

So many of these videos are brilliantly educational that I have started editing and improving the captions for people like myself who are hard-of-hearing or deaf. If you find my changes suitable, please use and alter them as you please. I have so far done this for two videos and intend to continue if you will approve the changes. It is the least I can do for such a great channel. :)

[Ostsol]

Funny how just the small hint of the title instantly made it clear to me just what the benefit of postfix notation was. I hadn't actually thought about it until now.

[IMortage]

I've always thought the Reverse Polish sounded like a Chess Opening. Which makes it even better.

[Chaosdude]

It's interesting to watch these coding videos because of the benefits it brings to my own logic. Coding is incredible at showing different ways to do the same thing. Before watching this video, I'd never thought in mathematical terms any different from infix notation. It's incredible to see how that suddenly changes the approach to the entire problem. Long story short, thank you for uploading these, Brady and Sean.

[Fhuaran]

Brailsford's videos just get better and better. It's like a story unfolding.

[Ghost]

I remember when I first learned about this a Comp. Sci. course at uni. The prof. was printing out a tree using a recursive method and just moved the print out statement between different conditions to convey the idea to us. Really cool stuff. :D

[Grngnak]

A number of years ago I tried learning a programming language that used RPN and couldn't quite understand how it all went together... I wish I had this video back then, it explains things very simply and make sense out of something that has had me confused for over a decade. Thank you professor!

[wattage]

Wonderful video. I first encountered an fell in love with RPN when I got my HP 32SII, back in high school. It was so great. You never needed parentheses and you could enter formulas by reading left to right. So nice to hear Prof. Brailsford explain the history and explain why it was so great.

[KaiserSpherical]

I remember having a similar reaction as Professor Brailsford here when I was first introduced to postfix notation and their relation to stacks. It's just brilliant! Absolutely a match made in heaven :D

[XNAforyou]

One of the most important videos for any Computer Scientist. The stack is a fundamental data structure.

[krishnaindani]

Just saw two videos on this channel and really impressed by the way they go into explaining it by doing into details. The professor is really amazing.

[intermarer]

Whoa, does this man have a playlist or something? What a great teacher! I feel I could watch him for hours and get super smart 😊

[aquere]

It's wonderful to see someone as passionate as this gentleman about his professional field

[ElectiveTool]

Please don't stop filming this wonderful man, and I won't stop watching :]