Re: Zero or not?

[Francesco Potorti`]

>> Stuff like sorting numbers by absolute value can help reduce the
>> error of the operations.
>
>This is one of methods of improvment in precission. But is very costly :(
>I made this method in one program twenty years ago ;)
>
>I can be done in octave in a simplest way:
>
>  [i,i]=sort(abs(x)); s=sum(x(i));

As far as I know, Octave does not give any guarantee as to the order in
which summation is done, so while this method may work for a particular
version of Octave, I do not think that it should be recommended.

Apart from academic discussion, when using 64-bit floating point numbers
it is rare to have problems with summation of same-sign quantities.  Why
do you care so much?  Maybe you have cancellation errors?

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