iFit/sw_extendlattice

 creates superlattice

 [mAtom AAext SSext] = SW_EXTENDLATTICE(nExt, mAtom, {SS}) 

 It creates a superlattice and all redefines all given bond for the larger
 superlattice.

 Input:

 nExt          Number of unit cell extensions, dimensions are [1 3].
 mAtom         Properties of the magnetic atoms, produced by sw.matom.
 SS            Interactions matrices in the unit cell, optional.

 Output:

 mAtom         Parameters of the magnetic atoms.
 mAtom.RRext   Positions of magnetic atoms, assuming an extended unit
               cell, dimensions are [3 nMagExt].
 mAtom.Sext    Spin length of the magnetic atoms, dimensions are
               [1 nMagExt].

 SSext         Interaction matrix in the extended unit cell, struct type.
               In the struct every field is a matrix. Every column of the
               matrices describes a single interaction.
 SSext.iso     Isotropic exchange interactions.
 SSext.ani     Anisotropic exchange interations.
 SSext.dm      Dzyaloshinsky-Moriya interaction terms.
 SSext.gen     General 3x3 matrix contains the exchange interaction.

 See also SW.INTMATRIX.