[gecode-users] int vs. unsigned int for Matrix dimensions
Gregory Crosswhite
gcross at phys.washington.edu
Tue Jan 25 20:42:52 CET 2011
Hey Christian,
Yes, I am fine with the WrapVal iterator being removed from the patch,
especially since it is not necessary for it to be in Gecode as it needs
no access to the internals of the arrays.
The tweaked patch and added documentation all look good to me as well.
So in summary, responding to all three of your queries: everything looks
fine to me --- thanks for including my patch in Gecode! :-)
Cheers,
Greg
On 01/25/2011 02:01 AM, Christian Schulte wrote:
>
> Hi,
>
> While I buy into the iterator stuff I have to admit that I am not
> (yet) excited over the wrap stuff: that looks very very specific.
> There are only few cases where you really can rely on the fact that
> variables are assigned.
>
> For example, a common misconception is that the print() function of a
> script can only be called on a solution and hence all variables are
> assigned. This is wrong, printing must also be able to deal with not
> yet assigned variables as the print function can be called on any
> script and not only solutions. This for example happens when you click
> a node in Gist.
>
> So I will include the iterators but not the wrap stuff. Is that okay?
>
> Thanks a lot for your effort!
>
> Christian
>
> --
>
> Christian Schulte, www.ict.kth.se/~cschulte/
>
> *From:*users-bounces at gecode.org [mailto:users-bounces at gecode.org] *On
> Behalf Of *Gregory Crosswhite
> *Sent:* Monday, January 24, 2011 10:57 PM
> *To:* users at gecode.org
> *Subject:* Re: [gecode-users] int vs. unsigned int for Matrix dimensions
>
> Oops, I just realized that I forgot to include in the patch an extra
> line in Makefile.in to install the new header. The amended patch is
> attached to this e-mail.
>
> Also, I forgot in my previous to mention that also included in the
> patch is a test for the WrapVal iterator in test/iter.hpp; that test
> program includes checks on some of the examples that I described in
> the e-mail to make sure that they have the expected result.
>
> Cheers,
> Greg
>
>
> On 01/24/2011 12:12 PM, Gregory Crosswhite wrote:
>
> Well then, I am glad that I got the patch ready over the weekend. :-)
>
> The patch has been attached to this e-mail as the file "patch"; it is
> the result of running "svn diff" against revision 11556.
>
> I have modified "gecode/kernel/array.hpp" along the lines that we
> discussed, and have added a new test to your suite under
> "test/array.cpp" to verify that it works as expected.
>
> While I was add it, I added another feature. The patch includes a
> file "gecode/iter/wrap-val.hpp" (and a patch to "gecode/iter.hh" to
> include this file) which contains an iterator class "WrapVal" that
> wraps another iterator and upon dereferencing returns the the result
> of calling ".val()" on the dereferenced wrapped iterator, as well as a
> function "wrap_val" that is a convenience function for constructing a
> "WrapVal" (since this causes the template parameters to automatically
> be inferred).
>
> That might sound complicated, but the point of it is to allow someone
> to do the following:
>
> #include <algorithm>
> #include <gecode/iter.hh>
> #include <iterator>
> #include <vector>
> ...
> using namespace Gecode;
> using namespace Gecode::Iter;
> using namespace std;
> ...
> IntVarArray a;
> ...
> vector<int> v;
> copy(wrap_val(a.begin()),wrap_val(a.end()),back_inserter(x));
>
> which has the effect of copying all of the values from the array a
> into the vector v, since a.begin() returns an iterator that
> dereferences to an IntVar and wrap_val(a.begin()) returns a wrapped
> iterator that returns the result of calling .val() on the IntVar.
>
> The basic use case of the iterators is as follows:
>
> IntVarArgs a;
> ...
> for(IntVarArgs::iterator i = a.begin(); i != a.end(); ++i) {
> rel(space,*i,IRT_EQ,0); }
>
> Of course, you could more easily do this with rel(space,a,IRT_EQ,0).
> A more interesting example is:
>
> IntVarArgs a;
> ...
> for(IntVarArgs::iterator i = a.begin(); i != a.end()-1; ++i) {
> rel(space,*i > *(i+1)+2); }
>
> More powerfully, iterators give you the ability to work with STL
> algorithms:
>
> #include <algorithm>
> ...
> void f(IntVar& v) { ... }
> ...
> IntVarArgs a;
> ...
> std::for_each(a.begin(),a.end(),f);
>
> The iterators returned by a.begin() and a.end() dereference to a
> reference to an IntVar/BoolVar (or a view in the case of ViewArray).
> If you are interested in iterating over the *values* of the array ---
> that is, the value currently assigned to to each variable then you can
> use the function wrap_val to wrap these iterators so that
> dereferencing them returns the value assigned to the variable. For
> example, the last two lines in the following have exactly the same
> result:
>
> #include <algorithm>
> #include <iostream>
> ...
> void f(IntVar& v) { std::cout << v.val() << " "; }
> void g(int i) { std::cout << i << " "; }
> ...
> IntVarArgs a;
> ...
> std::for_each(a.begin(),a.end(),f); std::cout << std::endl;
> std::for_each(wrap_val(a.begin()),wrap_val(a.end()),g); std::cout
> << std::endl;
>
> Or if you want to copy the values assigned to the variables into a
> std::vector:
>
> #include <algorithm>
> #include <iterator>
> #include <vector>
> ...
> IntVarArray a;
> ...
> std::vector<int> v;
>
> std::copy(wrap_val(a.begin()),wrap_val(a.end()),std::back_inserter(x));
>
> Or if you are interested in computing the sum of the values in the
> variables:
>
> #include <numeric>
> ...
> IntVarArray a;
> ...
> int sum = std::accumulate(wrap_val(a.begin()),wrap_val(a.end()),0);
>
> Or alternatively if you are interested in counting the number of zeros
> in the variables:
>
> #include <algorithm>
> ...
> IntVarArray a;
> ...
> unsigned int number_of_zeros =
> std::count(wrap_val(a.begin()),wrap_val(a.end()),0);
>
> ===
>
> Anyway, I hope that this patch can make it into Gecode this week; you
> have my official permission to release it under whatever license
> Gecode uses.
>
> Let me know if you have any questions! :-)
>
> Cheers,
> Gregory Crosswhite
>
>
>
> On 01/24/2011 10:54 AM, Christian Schulte wrote:
>
> Christian Schulte<cschulte at ...> <mailto:cschulte at ...> writes:
>
> Hi again,
>
> There is one thing I forgot to say: we intend to release end of this week
> (hopefully). So if your patch arrives until then, it'll be included in
> the
> next version.
>
> Cheers
> Christian
>
>
>
>
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