Online tools for mathematics

In this page i keep my favorite links for online mathematics tools:

Wolfram – Alpha:

One of my favorite sites. You can use it to visualize functions, solve equations etc

Two great sites for calculations for matrices:


Bash history expansion 🏅

The general syntax is:


Command segment defines which command to look for in history. It can be a modifier like !! (last command), !-1, !-2, !-3 … (last, previous to last etc) or a specific keyword like !cat (search for most recent cat).

Parameter segment defines which part of the command to use. ^ is first parameter, $ is last parameter, * are all the parameters, 0 the command and 1,2,3… are the parameters. You can define a range eg 2-4 (parameters 2 to 4)

Besides that, you can also use ^x^y^ to replace x with y. There are some more advanced ways to search. Take a look at the references at the end of this page.

You can also use history n to review the last n commands with their ids. If you know an id, you can use it at command segment,

All results are shown as if the command was executed immediately after touch a b c d e (not one after another)

Assume that you have typed in this order:

  1. ls -a -r
  2. date
  3. touch a b c d e
!! last command (all words) touch a b c d e
!* last command, all arguments a b c d e
!^ last command, second argument a
!$ last command, last argument e
!:0 first word touch
!:1 second word (first argument) a
!:2-4 range of words b c d
 ^touch^ls find touch and replace it with ls  ls a b c e d
!-1 last command touch a b c d e
!-2 previous to last command date
!-2:0 first keyword of previous to last command date
!ls:* search for command ls,
all arguments of ls
-a -r
!ls:^ search for command ls,
first argument of ls
!ls:$ search for command ls,
last argument of ls
!ls search for command starting from ls ls -a -r
!? b search for command containing b touch a b c d e
!!:gs/a/p/ last command, replace a with b touch p b c d e


Book recommendation:

UNIX Shells by Example, Ellie Quigley

Doom links

The Doom series Wiki

It includes complete walkthroughs for every map of every doom game. It includes story background, history, speedrun paths and instructions for all secrets on all maps. The only drawback is that secrets are explained with text.

This is a great site for Doom 1 and Doom 2 resources. It includes the maps of all episodes with options to display keys, teleports and secrets. Secrets and teleports are displayed visually on the maps.


Useful site with many reviews of the common WADs

You can find pseudo 3d projections of the maps.





I do not include links since they might change in the future, but if you google them you will easily find sites to download them.

  • Smooth Doom – It includes only visual improvements. No gameplay changes
  • Beautiful doom – It includes visual improvements. It also includes new weapons and some minor game play changes but they are mostly optional
  • Knee deep in zdoom – Imho a totally different game, but you can check it out


  • Winter’s fury

There are numerous other mods and WADs. I only include those I like.