[Boost-users] Help make boost::multi_array code generic!

Subject: [Boost-users] Help make boost::multi_array code generic!
From: Joey Mukherjee (joeymu_at_[hidden])
Date: 2010-02-23 19:37:18

I have some code which makes use of boost::multi_array that I would
like to make more generic, but I am incapable of groking the error
messages.  I am hoping some one can shed some light on this.

I have a one dimensional array of number which is actually a tensor of
variable size.   I have a vector (vinfo._sizes) which contains the
size of each of the dimensions.  In this case, I am using the 3D
version.  I have another vector (local_subsensors) which contains a
specific slice of the 3D view (i.e. reduce the 3D to 2D) that I am
seeking or a -1 to mean I want everything in the row/column.  I am
also given an X/Y variable to return out a specific value from this
new 2D matrix.

This code works in constructing a view of this type:

                    typedef boost::const_multi_array_ref <double, 3>array_type;
                    array_type::index_gen indices;
                    array_type multi_array (&(vals [0]), vinfo._sizes);

                    if ((local_subsensors [0] == -1)
&&(local_subsensors [1] == -1)) {
                        ret_val =
(array_type::const_array_view<2>::type (multi_array [indices [range
()][range()][local_subsensors[2]]])) [whichX][whichY];
                    } else
                    if ((local_subsensors [0] == -1)
&&(local_subsensors [2] == -1)) {
                        ret_val =
(array_type::const_array_view<2>::type (multi_array [indices
[range()][local_subsensors[1]][range()]])) [whichX][whichY];
                    } else
                    if ((local_subsensors [1] == -1)
&&(local_subsensors [2] == -1)) {
                        ret_val =
(array_type::const_array_view<2>::type (multi_array [indices
[local_subsensors[0]][range ()][range()]])) [whichX][whichY];
                    }

Here's my attempt at making this generic and it does not work.  Can
someone tell me why?

                    range Dim [3];

                    for (unsigned int i = 0; i < vinfo._sizes.size(); ++i)
                        if (local_subsensors [i] == -1) Dim [i] =range ();
                        else Dim [i] = range (local_subsensors [i]);

                    slice = multi_array [indices [Dim [0]][Dim [1]][Dim [2]]];

Thanks in advance!

Joey