[Boost-users] Help with a generic algorithm using boost::MultiArray

Subject: [Boost-users] Help with a generic algorithm using boost::MultiArray
From: Jesse Perla (jesseperla_at_[hidden])
Date: 2009-01-11 02:22:39

Hi:I would like to write an algorithm that operates on a multi-array and am
having trouble figuring out how to work with arbitrary numbers of
dimensions.  A simplified version of my problem that captures all of the
types of access I need is:
1) You have a multi-array of (statically defined at compilation)
dimensionality N.
2) This data is filled in, but the number of elements in each dimension will
frequently be different.
3) Write a function that takes a reference to this multiarray and assigns it
the value which is the sum of all of the actual indices(this is contrived,
but if I can solve this, I can solve my problem... The key is I need an
iterator moving through all dimensions, and I need the index numbers for my
calculations).
Here is some pseudocode that gives the kind of iterator I would love to
have:

template<int N>
void test_setting(multi_array<double, N>& arr)
{
//HERE IS PSEUDOCODE:  LETS SAY THERE WAS A WAY TO GET AN INDEX THAT YIELDED
THE ACTUAL INDEX NUMBERS BUT STILL ACTED AS A POINTER.
for(FANCYINDEX = arr.begin(); FANCYINDEX != arr.end(); ++FANCYINDEX)
{
boost::array<int, N> indicies = FANCYINDEX.get_indices(); //SAY IT RETURNED
THE ACTUAL NUMBERS
*FANCYINDEX = sum(indicies);
//Alternatively, could we go: arr(indicies) = sum(indices); if there is no
way for it to be a proper pointer.
}

}
//TO CALL:
const int NUMDIMS = 3; //Static at compile time.
int n1 = 3; //These might be dynamic.
int n2 = 4;
int n3 = 5;
boost::multi_array<double, NUMDIMS> A(boost::extents[n1][n2][n3]);
test_setting(A);

Any ideas on how this could be implemented without too much code?

Thanks,
Jesse