Classes var_lens_caten and con_lens_caten cause two matrices to appear to be combined into one. These lenses are smart enough to infer in which subscript position the catenation should take place, thus it need not be separately specified. As with all lenses, construction of a X_lens_caten does not alter the underlying matrices.

• The two input matrices must have equal dimensionalities; the output dimensionality will be the same as those. Consequently, two zero-dimensional matrices cannot be catenated.
• The forms of the input matrices must have equal blts in every position except one; and in that position the top value of the first matrix's blt must equal the bottom value of the second matrix's blt.

For example, this program:

#include "SOME_DIRECTORY/mat_gen_dim.h"
using namespace mat_gen_dim;

int main () {
    form const frm_a {blt{3,6},blt{2,4},blt{2,5}};
    cout << "\nfrm_a: " << frm_a;
    var_matrix<double> mat_a {sub_matrix_linear (frm_a, 1.0)};
    cout << "\nmat_a: " << mat_a;

    form const frm_b {blt{3,6},blt{4,6},blt{2,5}};
    cout << "\nfrm_b: " << frm_b;
    con_matrix<double> mat_b {sub_matrix_linear (frm_b, 2.0)};
    cout << "\nmat_b: " << mat_b;

    con_lens_caten<double> vac_c {mat_a, mat_b};
    cout << "\nfrm_c: " << vac_c.get_form();
    cout << "\nvac_c: " << vac_c;

    return 0;
}

frm_a: ( 3 =< 6, 2 =< 4, 2 =< 5 )
mat_a: 
    ( 3 2 2 ) = 1.322    ( 3 2 3 ) = 1.323    ( 3 2 4 ) = 1.324
    ( 3 3 2 ) = 1.332    ( 3 3 3 ) = 1.333    ( 3 3 4 ) = 1.334
    ( 4 2 2 ) = 1.422    ( 4 2 3 ) = 1.423    ( 4 2 4 ) = 1.424
    ( 4 3 2 ) = 1.432    ( 4 3 3 ) = 1.433    ( 4 3 4 ) = 1.434
    ( 5 2 2 ) = 1.522    ( 5 2 3 ) = 1.523    ( 5 2 4 ) = 1.524
    ( 5 3 2 ) = 1.532    ( 5 3 3 ) = 1.533    ( 5 3 4 ) = 1.534
frm_b: ( 3 =< 6, 4 =< 6, 2 =< 5 )
mat_b: 
    ( 3 4 2 ) = 2.342    ( 3 4 3 ) = 2.343    ( 3 4 4 ) = 2.344
    ( 3 5 2 ) = 2.352    ( 3 5 3 ) = 2.353    ( 3 5 4 ) = 2.354
    ( 4 4 2 ) = 2.442    ( 4 4 3 ) = 2.443    ( 4 4 4 ) = 2.444
    ( 4 5 2 ) = 2.452    ( 4 5 3 ) = 2.453    ( 4 5 4 ) = 2.454
    ( 5 4 2 ) = 2.542    ( 5 4 3 ) = 2.543    ( 5 4 4 ) = 2.544
    ( 5 5 2 ) = 2.552    ( 5 5 3 ) = 2.553    ( 5 5 4 ) = 2.554
frm_c: ( 3 =< 6, 2 =< 6, 2 =< 5 )
vac_c: 
    ( 3 2 2 ) = 1.322    ( 3 2 3 ) = 1.323    ( 3 2 4 ) = 1.324
    ( 3 3 2 ) = 1.332    ( 3 3 3 ) = 1.333    ( 3 3 4 ) = 1.334
    ( 3 4 2 ) = 2.342    ( 3 4 3 ) = 2.343    ( 3 4 4 ) = 2.344
    ( 3 5 2 ) = 2.352    ( 3 5 3 ) = 2.353    ( 3 5 4 ) = 2.354
    ( 4 2 2 ) = 1.422    ( 4 2 3 ) = 1.423    ( 4 2 4 ) = 1.424
    ( 4 3 2 ) = 1.432    ( 4 3 3 ) = 1.433    ( 4 3 4 ) = 1.434
    ( 4 4 2 ) = 2.442    ( 4 4 3 ) = 2.443    ( 4 4 4 ) = 2.444
    ( 4 5 2 ) = 2.452    ( 4 5 3 ) = 2.453    ( 4 5 4 ) = 2.454
    ( 5 2 2 ) = 1.522    ( 5 2 3 ) = 1.523    ( 5 2 4 ) = 1.524
    ( 5 3 2 ) = 1.532    ( 5 3 3 ) = 1.533    ( 5 3 4 ) = 1.534
    ( 5 4 2 ) = 2.542    ( 5 4 3 ) = 2.543    ( 5 4 4 ) = 2.544
    ( 5 5 2 ) = 2.552    ( 5 5 3 ) = 2.553    ( 5 5 4 ) = 2.554