Purpose: Usage help for the sqrt math function.
The call,
[expr { sqrt($x) }]
returns the square root of $x.
If you're using sqrt in connection with the Pythagorean Theorem:
[expr { sqrt( $x * $x + $y * $y ) }]
note that Tcl provides a hypot function, which gives a more concise formula:
[expr { hypot( $x, $y ) }]
The hypot function is also more robust in that it will get overflow and underflow less often when dealing with very large or very small numbers.
See also: isqrt