why cell arrays are used in 'interp2'

[Sergei Steshenko]

Hello,

looking into 'octave-3.6.2/share/octave/3.6.2/m/general/interp2.m' file I see:

"
    265       ## construct the cubic hermite base functions in x, y
    266
    267       ## formulas:
    268       ## b{1,1} =    ( 2*t.^3 - 3*t.^2     + 1);
    269       ## b{2,1} = h.*(   t.^3 - 2*t.^2 + t    );
    270       ## b{1,2} =    (-2*t.^3 + 3*t.^2        );
    271       ## b{2,2} = h.*(   t.^3 -   t.^2        );
    272
    273       ## optimized equivalents of the above:
    274       t1 = tx.^2;
    275       t2 = tx.*t1 - t1;
    276       xb{2,2} = hx.*t2;
    277       t1 = t2 - t1;
    278       xb{2,1} = hx.*(t1 + tx);
    279       t2 += t1;
    280       xb{1,2} = -t2;
    281       xb{1,1} = t2 + 1;
    282
    283       t1 = ty.^2;
    284       t2 = ty.*t1 - t1;
    285       yb{2,2} = hy.*t2;
    286       t1 = t2 - t1;
    287       yb{2,1} = hy.*(t1 + ty);
    288       t2 += t1;
    289       yb{1,2} = -t2;
    290       yb{1,1} = t2 + 1;
    291
    292       ZI = zeros (size (XI));
    293       for i = 1:2
    294         for j = 1:2
    295           zidx = sub2ind (size (Z), yidx+(j-1), xidx+(i-1));
    296           ZI += xb{1,i} .* yb{1,j} .*   Z(zidx);
    297           ZI += xb{2,i} .* yb{1,j} .*  DX(zidx);
    298           ZI += xb{1,i} .* yb{2,j} .*  DY(zidx);
    299           ZI += xb{2,i} .* yb{2,j} .* DXY(zidx);
    300         endfor
    301       endfor

".

It looks to me only numeric data is used as array elements, so why cell arrays 
and not regular 2d matrices ?

Speed ? Space ? Something else I couldn't think of ?


Thanks,
  Sergei.