Re: Magnitude of Order "For Loop" performance deltas based on syntax change

[Chet Ramey]

On 9/24/16 8:29 AM, Christian Franke wrote:

> - Method-2 could be significantly speed up if the order of the array
> accesses is reversed:
> 
>   for (( i=0; i<N-1; i++)); do
>       if (( -(Pi[i] - Pi[i+1]) < min )); then
>           min=$((-(Pi[i]-Pi[i+1])))
>       fi
>   done
> 
> Result: ~3 seconds
> (using 'let' in the 'min' assignment failed with syntax error - Bug?)

I assume you mean that you used something like

        let min=-(Pi[i]-Pi[i+1])

That's a syntax error because `(' is a shell operator, and it needs to be
quoted if you want it to appear in a word.  Since `let' is a builtin, not
part of the shell syntax, you have to make sure that all arguments to it
are valid shell words.

Chet
-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/