Introduction to Octave

1. help -i svd

2. Type q to exti help mode

3. Numerical Precision, variables are stored as double precision numbers in IEEE floating pointing format

    realmin : Smallest positive floating point number 2.23e-308

    realmax : Largest positive floating point number 1.80e-308

    eps : Relative precision 2.22e-16

4. rows(A) : Get number of rows of A

     columns(A) : Get number of columns of A

5. Exporting figures

    print -deps myPicBW.eps ---------------Export B/W .eps file

    print -depsc myPic.eps    ----------------Export color .eps file

    print -djpeg -r80 myPic.jpg --------------Export .jpg in 80 ppi

    print -dpng -r100 myPic.png -----------Export .png in 100ppi

See help print for more devices including specialized ones for latex.

print can also be called as a function

6. After a complex of lengthy computation, it is recommended to save variabls on the disk

   save my_vars.mat

7. For Unix/Linux/MacOSX systems, there is the command unix to execute system commands and return

    the result.

    Examples:

    unix('ls -al')

    unix('ftp < ftp_script')

    unix ('./myprogram')

8.   Hack the speed issue

a. For-loops are evil

b. Vectorization is good

c. Preallocation is good   

d. Prefer struct of arrays over arrays of struct