Code covered by the BSD License

### Highlights from3D Free Form Image Registration Toolbox (GUI)

from 3D Free Form Image Registration Toolbox (GUI) by Daniel Markel
A toolbox for performing image registrations on 4D RTOG files or any other volumetric image.

ddLdydPy(base,sz2,sz,m,n,i1,j1)
```%determine the change in deformation in the x direction for the mth by nth
%control point
function values = ddLdydPy(base,sz2,sz,m,n,i1,j1)
sz3 = size(base);
[y,x] = find(base >= 0);
locations = find(base >= 0);
X = zeros(sz3(1),sz3(2));
Y = zeros(sz3(1),sz3(2));
X(locations) = x(locations)+j1;
Y(locations) = y(locations)+i1;
values = zeros(sz3(1),sz3(2));
dvdy = (sz2(1)-3)/sz(1);

i = floor(((Y-0.5).*(sz2(1)-3)./sz(1))+2)-1;
j = floor(((X-0.5).*(sz2(2)-3)./sz(2))+2)-1;
indices = find( m-i >=0 & m-i <=3 & n-j >=0 & n-j <=3);
%             u = X(indices).*sz2(2)./sz(2) - floor(X(indices).*sz2(2)./sz(2));
%             v = Y(indices).*sz2(1)./sz(1) - floor(Y(indices).*sz2(1)./sz(1));
%             u = rem(X(indices),(sz(2)/((sz2(2)-3))+1));
%             v = rem(Y(indices),(sz(1)/((sz2(1)-3))+1));
u = ((X(indices)-0.5).*(sz2(2)-3)./sz(2))+2 - floor(((X(indices)-0.5).*(sz2(2)-3)./sz(2))+2);
v = ((Y(indices)-0.5).*(sz2(1)-3)./sz(1))+2 - floor(((Y(indices)-0.5).*(sz2(1)-3)./sz(1))+2);
ysum = bspline(u,n-j(indices)).*dbspline(v,m-i(indices)).*dvdy;

values(indices) = ysum;

```