MATLAB: Image registration with Gradient descent

updating rotation

I am trying to register two images based on gradient descent and sum square difference between two images. however, i have problem to update my transform matrix in each iteration. it can update translation but when i add rotation it just cant provide any correct results.
the following code is belongs to gradient descent with respect to translation and rotation:
[gy gx]=gradient(registerimage);
dx=sum(2*(gx(:)).*(referenceimage-registerimage(:)));
dy=sum(2*(gy(:)).*(referenceimage-registerimage(:)));
for i=1:128 (pixel position of registered image)
    for j=1:128
Ir(i,j)=((-j)*gx(i,j))+(i*gy(i,j));
    end
end
dr=sum(2*(Ir(:)).*(referenceimage-registerimage(:)));
after finding these gradient decent the following code has been used in order to update translation part of transform matrix:
trans(1,3)=trans(1,3)+currentStepSize*dx/lenght;
trans(2,3)=trans(2,3)+currentStepSize*dy/lengh
at the begining of program transform matrix defined as eye(3), current step size (learning rate of gradient) is define as 0.5 but it will increase or decrease by factor of 2 based on the results of each iteration
and length is:
lenght=sqrt(dx^2+dy^2);
Now i have problem to change trans(1,1),trans(1,2),trans(2,1) and trans(2,2) which are belong to rotation part. i will be glad to have your comments on it becuase i really stuck.
Thanks

Best Answer

Did you really code a variable named "lengh" and another named "lenght", both of which are confusingly close to the name of the built-in function "length" ?
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