3.1   2007-08-05 maxima

don't omit * for multiplication when it comes to multiplication between parenthesis. otherwise, it'll be regarded as function. for example:

a*(b+c) ; this is the correct form to express multiply a with b+c.
a(b+c) ; this is calling a function, a() with b+c as argument.

comment in maxima begins with a semi-colon (;). same as lisp.

2008-04-29 solve quadratic equation:

solve(Hw = s*(1/2*Hw+1/2)+(1-s)*Hb, Hw);
ev(Hb=1/N*((1-u)^2*1/2+1/2*(1-u)^2*Hw)+(1-1/N)*(1-u)^2*Hb, Hw: (1/2*s+(1-s)*Hb)/(1-1/2*s));  (or ev(Hb=1/N*((1-u)^2*1/2+1/2*(1-u)^2*Hw)+(1-1/N)*(1-u)^2*Hb, %o1);
solve(%o2, Hb);

4.1   2007-09-20 use gscan2pdf to add one missing page into a pdf file

import the old pdf file

scan the missing page

save that single missing page into a pdf

import that single page pdf and delete the old scanned page

save all into one pdf

Note: the reason to save that one single page out as pdf is that if you don't do that, that scanned page ends up with a much smaller size compared to other pdf-imported pages. It might be caused by the fact that old pages were scanned in color mode and new page was scanned in gray mode.

6.1   2007-11-06 autocompletion

While still in insert-mode, one can auto-complete a word by either searching forwards(hit Ctrl-N) or backwards(Ctrl-P).

6.2   2007-11-06 copy a set of columns using visual block(AKA column-wise selection).

<C-V> then select "column(s)" with motion commands (win32 <C-Q>) then c,d,y,r etc. (http://rayninfo.co.uk/vimtips.html)

6.3   2007-12-04 spell check (command 'aspell -c filename' has similar function)

enable spell check by ':set spell', disable by ':set nospell', get help by ':help spell'

']s': Move to next misspelled word after the cursor.

'zg': Add word under the cursor as a good word to the first name in 'spellfile'.

'zG': Like "zg" but add the word to the internal word list.

'z=': find suggestions for words (not just bad/highlighted words)

2007-12-21 vim quick references http://tnerual.eriogerg.free.fr/vimqrc.html

6.4   2008-03-16 group patterns by \( \).

Following line is to repeat content on each line 3 time and append C, T.:

g/\(.*\)$/s//\1\t\1\t\1\tC\tT/

6.5   2008-4-2 substitute using a register

examples:

:s/fred/<c-r>a/g            : sub "fred" with contents of register "a"
:s/fred/<c-r>asome_text<c-r>s/g  
:s/fred/\=@a/g              : better alternative as register not displayed

setup a register by visual-selecting a region and then press "ay to put the region into register a.

6.6   2008-05-30 taglist

vim-taglist provides an overview of the structure of source code files and allows you to efficiently browse through source code files in different programming languages.

installation:

1. download 4.5 from http://vim.sourceforge.net/scripts/download_script.php?src_id=7701
2. unzip in /tmp/
3. cp /tmp/plugin/taglist.vim /usr/share/vim/vim71/plugin/
4. cp /tmp/doc/taglist.txt /usr/share/vim/vim71/doc/

caveat:

1. run ctags in the working directory to have the tags file setup so that TlistToggle would work. however the vimplugin in eclipse seems doesn't need this ctags step.
2. not sure the other plugin directory, /usr/share/vim/addons/plugin/ has the same effect or not.

6.7   2008-05-30 word_complete

http://www.vim.org/scripts/script.php?script_id=73

1. download word_complete.vim and put it in /usr/share/vim/vim71/plugin/.
2. type :call DoWordComplete() in vi

6.8   2009-2-4 binary/hexdecimal mode

1. edit the file in binary mode (dos carriage return would be visible):

   vim -b datafile
   

2. Many characters in the file will be unprintable. To see them in Hex format:

   :set display=uhex
   

3. hexdecimal mode:

   1. open the file in binary mode:

      vim -b datafile
      

   2. Now convert the file to a hex dump with xxd:

      :%!xxd
      

   3. convert it back with:

      :%!xxd -r
      

4. to replace the dos carriage return and line feed (rn) with just unix line feed (n). g/\r\n/s//\n/ doesn't work.:

   :g/.$/s///
   
   or
   
   :g/\r/s///
   
   ``dos2unix`` is another alternative.
   

5. to replace the dos carriage return (r) (all lines are on one line in vi or less) with unix line feed (n) (separating stuff jammed in one line into multi-line) .:

   :g/\r/s//\r/g
   

7.1   2007-12-09 change user id

need to change the user id of crocea to avoid the id clash between crocea and diradmin from papaya::

usermod -u 10000 crocea

usermod will automatically change the id of all files in the home directory but others outside have to be changed manually.

cron and/or mail daemon(exim4) might need to restart to ensure the new user id is used. otherwise, /var/log/exim4/paniclog might give out errors as "Failed to get user name for uid 1000".

7.2   2008-05-05 add an existing user to a group

http://www.cyberciti.biz/faq/howto-linux-add-user-to-group/

add user tony to group ftp:

usermod -a -G ftp tony