Hi Birger,
The possibility to compute & store the max/minimum per leaf
is already foreseen in the TLeaf classes. It is currently
only filled for leaves that represent a branch count.
I did not implement it yet because there are cases where
it does not make sense (a TLeaf is an object) or it is ambiguous,
and time consuming for example arrays.
For example, I had several requests to process fixed length arrays
separately from variable length arrays.
In case of variable length arrays, one can assume homogeneous info
inside the array. For fix length, some people store a[0] = something,
a[1]= something else. In this case min/max have no meaning except
for each element of the array.
Another reason why GetMinimum,Maximum, loop on all entries was that
I was thinking to extend the meaning of the parameter to be an expression
of the original variables. However, this could be two separate functions.
I agree with your remark with the 1e30. There are a few other places
where this constant appear and should be changed as you propose.
Thanks for your remarks.
Rene Brun
On Fri, 3 Dec 1999, Birger Koblitz wrote:
> Hi,
>
> I noticed that TNtuple::GetMaximum(Text_t *) takes a significant amount of
> time. Obviously it loops over all entries and calculates the maximum. This
> is of course very slow. Wouldn't it be possible to calculate this
> information while the NTuple is filled? I don't think it is very difficult
> to implement and it would be quite usefull, especially if one needs some
> bounds e.g. before one wants to fill a histogram with the information of
> the ntuple. What was said is of course also true for GetMinimum.
> Actually I encountered the problem while porting some kumac from paw where
> this seems to be implemented, and I don't think that root should lack
> anything paw features, right ;-) ?
> So, Rene, would it be possible for you to implement this feature in the
> next release?
>
> Cheers,
> Birger
>
> PS: Looking at the source, one actually finds:
>
> Float_t TTree::GetMinimum(const char *columname)
> {
>
> TLeaf *leaf = GetLeaf(columname);
> if (!leaf) return 0;
> TBranch *branch = leaf->GetBranch();
> Float_t cmin = 1e30; <============ ?????
> for (Int_t i=0;i<fEntries;i++) {
> branch->GetEntry(i);
> Float_t val = leaf->GetValue();
> if (val < cmin) cmin = val;
> }
> return cmin;
> }
>
> obviously there is a bug in the marked line, because it makes assumptions
> about the representation of float values on the machine: it assumes
> 1e30 to be the largest float value which is false on most machines. One
> should either initialize with the first entry or with FLOATMAX calculated
> in math.h or values.h. Sorry for being pedantic, but numerics is something
> to take seriously...
>
>
>
> /------------------------------------------------------------\
> | Birger Koblitz koblitz@mail.desy.de |
> | Max-Planck-Institut fuer Physik |
> | (Werner Heisenberg-Institut) |
> | DESY-FH1K Tel. (40) 8998-3971 |
> | Notkestr. 85 |
> | D-22603 HAMBURG |
> \------------------------------------------------------------/
>
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