Advanced techniques for solving tough Sudoku

[Activation Mail]

Advanced techniques for solving tough Sudoku. You know some mathematical formula or something.

If anybody knows, please post it here. I Googled but all I found were the 'elimination methods' I had guessed by myself or techniques having at least a slight element of partial trial-and-error. Not techniques or tricks in real sense.

[kalidas]

Here's the technique I use:

First make sure that numbers in each square is 1-9.
Then make sure that the number does not exist in vertical or horizontal row
Look at all options that possible. If there is one and only one number that fits the cell, then use it
Move to the next cell.

First finish the obvious ones
Then rinse and repeat. Few more ones will pop out
When you are grid locked, then focus on the square with least filled out cells and try to get them in.
If you have a full line completed in a square then look for numbers that are not there, but in other squares that can be filled in the subsequent row. That will narrow it down. Usually you can find one or two numbers this way.
Pick the square that has maximum vertical/horizontal numbers listed so you can reduce the number of options. Say you have 2 possible numbers, put one number in there mentally and follow the logic. Usually you will reach a dead end or everything will magically fall in place.
If you understood everything I said, you will have no problems solving even the hardest Sudoku in the history of man.

[kalidas]

Today, I saw a complex Sudoku puzzle. I used above technique to solve it.