help-octave
[Top][All Lists]

## why cell arrays are used in 'interp2'

 From: Sergei Steshenko Subject: why cell arrays are used in 'interp2' Date: Mon, 24 Dec 2012 19:25:14 -0800 (PST)

```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.

```