On Sat, Jan 14, 2023 at 1:48 PM Sven Schreiber
<sven.schrei...@fu-berlin.de> wrote:
>
> Am 14.01.2023 um 19:37 schrieb Cottrell, Allin:
>
> On Sat, Jan 14, 2023 at 12:48 PM Sven Schreiber
> <sven.schrei...@fu-berlin.de> wrote:
>
> ...
>
> I just tried the Jan 1 and Jan 10 Windows snapshots, in both English
> and German, and saw no such error. I can't really believe in this
> error without seeing a screenshot where the relevant commands are
> prefaced by "clear".
>
> OK, I explicitly uninstalled gretl and re-installed the same snapshot, and
> indeed the error is gone. Perhaps there was some confusion across the
> scripts and the console. One less thing to worry about!
Glad to hear it.
> Right, OK. So what's actually recommended in those and similar cases, using
> the mols() function or the "/" or "\" operators? (Provided the residuals
> aren't wanted afterwards, which are only provided by mols.)
>
> Is a recommendation really called for here? I mean, do as you please:
> the results will be the same to machine precision.
>
> I meant if some speed difference is to be expected, or if it's calling into
> the same underlying BLAS routines anyway.
OK, I see. "/" calls QR decomposition, while mols() calls Cholesky
with a fallback to QR in case of near-perfect collinearity. So mols()
will be a bit faster unless the fallback is required.
<hansl>
A = ones(4,3)
B = {1, 0.2, 5}
set stopwatch
loop 10000
x = A / B
endloop
t1 = $stopwatch
Y = A'
X = B'
set stopwatch
loop 10000
b = mols(Y, X)
endloop
t2 = $stopwatch
printf "right-division %.3fs, mols %.3fs\n", t1, t2
</hansl>
Here I get: right-division 0.021s, mols 0.014s
Allin
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