From maechler at stat.math.ethz.ch  Sat Aug 19 14:47:25 2017
From: maechler at stat.math.ethz.ch (Martin Maechler)
Date: Sat, 19 Aug 2017 14:47:25 +0200
Subject: [Rd] Issues of R_pretty in src/appl/pretty.c
In-Reply-To: <973411292.327791.1503071046156@mail.yahoo.com>
References: <973411292.327791.1503071046156.ref@mail.yahoo.com>
 <973411292.327791.1503071046156@mail.yahoo.com>
Message-ID: <22936.13149.795298.273855@stat.math.ethz.ch>

>>>>> Suharto Anggono Suharto Anggono via R-devel <r-devel at r-project.org>
>>>>>     on Fri, 18 Aug 2017 15:44:06 +0000 writes:

    > Examples similar to
    > pretty(c(-1,1)*1e300, n = 1e9, min.n = 1)
    > with smaller 'n':
    > pretty(c(-1,1)*1e304, n = 1e5, min.n = 1)
    > pretty(c(-1,1)*1e306, n = 1e3, min.n = 1)


Thank you.

"But" all these work now (in R-devel, rev >= 73094) as they should,
at least for me, right?

Are you mentioning the  "small n" examples so we could use them
as regression tests  (instead of the regression test I had added
to tests/reg-large.R  which needs enough GB and is slowish ) --
or are you seeing a platform where the above cases still don't
work in (new enough) R-devel ?


    > A report on 'pretty' when working with integers, similar to what led to change of 'seq' fuzz, is https://bugs.r-project.org/bugzilla3/show_bug.cgi?id=15137

    > --------------------------------------------
    > On Tue, 15/8/17, Martin Maechler <maechler at stat.math.ethz.ch> wrote:

    > Subject: Re: [Rd] Issues of R_pretty in src/appl/pretty.c
    > To: "Martin Maechler" <maechler at stat.math.ethz.ch>

    > @r-project.org
    > Date: Tuesday, 15 August, 2017, 3:55 PM

>>>>> Martin Maechler <maechler at stat.math.ethz.ch>
    >>>>>> ? ?? on Mon, 14 Aug 2017 11:46:07 +0200 writes:

>>>>> Suharto Anggono Suharto Anggono via R-devel <r-devel at r-project.org>
    >>>>>> ? ?? on Fri, 11 Aug 2017 17:11:06 +0000 writes:
>>>>> Suharto Anggono Suharto Anggono via R-devel <r-devel at r-project.org>
    >>>>>> ? ?? on Fri, 11 Aug 2017 17:11:06 +0000 writes:

    > ? ? >> See https://stat.ethz.ch/pipermail/r-devel/2017-August/074746.html for the origin of the example here.

    > ? ? >> That
    > ? ? >> pretty(c(-1,1)*1e300, n = 1e9, min.n = 1) gave 20 intervals, far from 1e9, but
    > ? ? >> pretty(c(-1,1)*1e300, n = 1e6, min.n = 1) gave 1000000 intervals
    > ? ? >> (on a machine), made me trace through the code to function 'R_pretty' in https://svn.r-project.org/R/trunk/src/appl/pretty.c .

    > ? ? > thank you.

    > ? ? >> *lo is -1e300, *up is 1e300.
    > ? ? >> cell = fmax2(fabs(*lo),fabs(*up));
    > ? ? >> 'cell' is 1e300.
    > ? ? >> i_small = dx < cell * U * imax2(1,*ndiv) * DBL_EPSILON *3;
    > ? ? >> When *ndiv is (int) 1e9, apparently cell * U * imax2(1,*ndiv) overflows to infinity and 'i_small' is 1 (true). It doesn't happen when *ndiv is (int) 1e6.

    > [[elided Yahoo spam]]

    > ? ? >> Putting parentheses may avoid the floating point overflow. For example,
    > ? ? >> i_small = dx < cell * (U * imax2(1,*ndiv) * DBL_EPSILON) *3;

    > ? ? > yes... but only if the compiler optimization steps? "keep the parentheses".
    > ? ? > AFAIK, there is no guarantee for that.
    > ? ? > To make sure, I'd replace the above by

    > ? ? > U *= imax2(1,*ndiv) * DBL_EPSILON;
    > ? ? > i_small = dx < cell * U * 3;


    > ? ? >> The part
    > ? ? >> U = (1 + (h5 >= 1.5*h+.5)) ? 1/(1+h) : 1.5/(1+h5);
    > ? ? >> is strange. Because (h5 >= 1.5*h+.5) is 1 or 0, (1 + (h5 >= 1.5*h+.5)) is never zero and 1/(1+h) will always be chosen.

    > [[elided Yahoo spam]]
    > ? ? > here was as a change (not by me!) adding wrong parentheses
    > ? ? > there (or maybe adding what the previously "missing" parens
    > ? ? > implied, but not what they intended!).
    > ? ? > The original code had been
    > ? ?? 
    > ? ? > U = 1 + (h5 >= 1.5*h+.5) ? 1/(1+h) : 1.5/(1+h5);

    > ? ? > and "of course" was intended to mean

    > ? ? > U = 1 + ((h5 >= 1.5*h+.5) ? 1/(1+h) : 1.5/(1+h5));

    > ? ? > and this what I'll change it to, now.


    > ? ? >> The comment for 'rounding_eps' says "1e-7 is consistent with seq.default()". Currently, seq.default() uses 1e-10 as fuzz.

    > ? ? > Hmm, yes, thank you; this was correct when written,
    > ? ? > but seq.default had been changed in the mean time,
    > ? ? > namely in? svn r51095 | 2010-02-03

    > ? ? > Usually we are cautious / reluctant to change such things w/o
    > ? ? > any bug that we see to fix.
    > ? ? > OTOH, we did have? bug cases we'd wanted to amend for seq() /
    > ? ? > seq.int();
    > ? ? > and I'll look into updating the "pretty - epsilon" also to
    > ? ? > 1e-10.

    > [[elided Yahoo spam]]

    > I've committed now what I think has been suggested
    > above ... to R-devel only :
    > ------------------------------------------------------------------------
    > r73094 | maechler | 2017-08-15 09:10:27 +0200 (Tue, 15. Aug 2017) | 1 Zeile
    > Ge?nderte Pfade:
    > ?? M doc/NEWS.Rd
    > ?? M src/appl/pretty.c
    > ?? M src/main/engine.c
    > ?? M tests/reg-large.R
    > ?? M tests/reg-tests-2.Rout.save

    > pretty(x, n) fix overflow for large n suggested by Suhartu Aggano, R-devel, 2017-08-11

    > ______________________________________________
    > R-devel at r-project.org mailing list
    > https://stat.ethz.ch/mailman/listinfo/r-devel



    > --------------------------------------------
    > On Tue, 15/8/17, Martin Maechler <maechler at stat.math.ethz.ch> wrote:

    > Subject: Re: [Rd] Issues of R_pretty in src/appl/pretty.c
    > To: "Martin Maechler" <maechler at stat.math.ethz.ch>

    > @r-project.org
    > Date: Tuesday, 15 August, 2017, 3:55 PM

>>>>> Martin Maechler <maechler at stat.math.ethz.ch>
    >>>>>> ? ?? on Mon, 14 Aug 2017 11:46:07 +0200 writes:

>>>>> Suharto Anggono Suharto Anggono via R-devel <r-devel at r-project.org>
    >>>>>> ? ?? on Fri, 11 Aug 2017 17:11:06 +0000 writes:
>>>>> Suharto Anggono Suharto Anggono via R-devel <r-devel at r-project.org>
    >>>>>> ? ?? on Fri, 11 Aug 2017 17:11:06 +0000 writes:

    > ? ? >> See https://stat.ethz.ch/pipermail/r-devel/2017-August/074746.html for the origin of the example here.

    > ? ? >> That
    > ? ? >> pretty(c(-1,1)*1e300, n = 1e9, min.n = 1) gave 20 intervals, far from 1e9, but
    > ? ? >> pretty(c(-1,1)*1e300, n = 1e6, min.n = 1) gave 1000000 intervals
    > ? ? >> (on a machine), made me trace through the code to function 'R_pretty' in https://svn.r-project.org/R/trunk/src/appl/pretty.c .

    > ? ? > thank you.

    > ? ? >> *lo is -1e300, *up is 1e300.
    > ? ? >> cell = fmax2(fabs(*lo),fabs(*up));
    > ? ? >> 'cell' is 1e300.
    > ? ? >> i_small = dx < cell * U * imax2(1,*ndiv) * DBL_EPSILON *3;
    > ? ? >> When *ndiv is (int) 1e9, apparently cell * U * imax2(1,*ndiv) overflows to infinity and 'i_small' is 1 (true). It doesn't happen when *ndiv is (int) 1e6.

    > [[elided Yahoo spam]]

    > ? ? >> Putting parentheses may avoid the floating point overflow. For example,
    > ? ? >> i_small = dx < cell * (U * imax2(1,*ndiv) * DBL_EPSILON) *3;

    > ? ? > yes... but only if the compiler optimization steps? "keep the parentheses".
    > ? ? > AFAIK, there is no guarantee for that.
    > ? ? > To make sure, I'd replace the above by

    > ? ? > U *= imax2(1,*ndiv) * DBL_EPSILON;
    > ? ? > i_small = dx < cell * U * 3;


    > ? ? >> The part
    > ? ? >> U = (1 + (h5 >= 1.5*h+.5)) ? 1/(1+h) : 1.5/(1+h5);
    > ? ? >> is strange. Because (h5 >= 1.5*h+.5) is 1 or 0, (1 + (h5 >= 1.5*h+.5)) is never zero and 1/(1+h) will always be chosen.

    > [[elided Yahoo spam]]
    > ? ? > here was as a change (not by me!) adding wrong parentheses
    > ? ? > there (or maybe adding what the previously "missing" parens
    > ? ? > implied, but not what they intended!).
    > ? ? > The original code had been
    > ? ?? 
    > ? ? > U = 1 + (h5 >= 1.5*h+.5) ? 1/(1+h) : 1.5/(1+h5);

    > ? ? > and "of course" was intended to mean

    > ? ? > U = 1 + ((h5 >= 1.5*h+.5) ? 1/(1+h) : 1.5/(1+h5));

    > ? ? > and this what I'll change it to, now.


    > ? ? >> The comment for 'rounding_eps' says "1e-7 is consistent with seq.default()". Currently, seq.default() uses 1e-10 as fuzz.

    > ? ? > Hmm, yes, thank you; this was correct when written,
    > ? ? > but seq.default had been changed in the mean time,
    > ? ? > namely in? svn r51095 | 2010-02-03

    > ? ? > Usually we are cautious / reluctant to change such things w/o
    > ? ? > any bug that we see to fix.
    > ? ? > OTOH, we did have? bug cases we'd wanted to amend for seq() /
    > ? ? > seq.int();
    > ? ? > and I'll look into updating the "pretty - epsilon" also to
    > ? ? > 1e-10.

    > [[elided Yahoo spam]]

    > I've committed now what I think has been suggested
    > above ... to R-devel only :
    > ------------------------------------------------------------------------
    > r73094 | maechler | 2017-08-15 09:10:27 +0200 (Tue, 15. Aug 2017) | 1 Zeile
    > Ge?nderte Pfade:
    > ?? M doc/NEWS.Rd
    > ?? M src/appl/pretty.c
    > ?? M src/main/engine.c
    > ?? M tests/reg-large.R
    > ?? M tests/reg-tests-2.Rout.save

    > pretty(x, n) fix overflow for large n suggested by Suhartu Aggano, R-devel, 2017-08-11



[Rd] Issues of R_pretty in src/appl/pretty.c
Martin Maechler