how to reduce the running time (preallocate)

function[A,Y_linear2,ksi] = iteration(x0,y0,xp,yp,X_target,X_true,x,y,ksi0,Input);
syms omega phi kappa;
R_omega=[1 0 0 ; 0 cos(omega) -sin(omega) ; 0 sin(omega) cos(omega)];
R_phi=[cos(phi) 0 sin(phi) ; 0 1 0 ; -sin(phi) 0 cos(phi)];
R_kappa=[cos(kappa) -sin(kappa) 0 ; sin(kappa) cos(kappa) 0 ; 0 0 1];

R=R_omega*R_phi*R_kappa;
r11=R(1); r21=R(2);r31=R(3);r12=R(4);r22=R(5);r32=R(6);r13=R(7);r23=R(8);r33=R(9);

syms X0 Y0 Z0


for i = 1:length(X_target)
    Y_linear2(2*i-1) = [x(i)-x0(i)];
    Y_linear2(2*i)= [y(i)-y0(i)];
end

if Input == 'DSC00370.jpg'
    A = [jacobian([x0(1)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(1)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(2)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(2)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(3)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(3)-xp],[X0,Y0,Z0,omega,phi,kappa]);...
    jacobian([x0(4)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(4)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(5)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(5)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(6)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(6)-xp],[X0,Y0,Z0,omega,phi,kappa])];
elseif Input == 'DSC00371.jpg'
    A = [jacobian([x0(1)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(1)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(2)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(2)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(3)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(3)-xp],[X0,Y0,Z0,omega,phi,kappa]);...
    jacobian([x0(4)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(4)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(5)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(5)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(6)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(6)-xp],[X0,Y0,Z0,omega,phi,kappa]);...
    jacobian([x0(7)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(7)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(8)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(8)-xp],[X0,Y0,Z0,omega,phi,kappa])];
end

%%del_ksi = inv(A'*eye(6)*A)*A'*eye(6)*(Y_linear)';

n=1;
while (n<3);
   del_ksi = (A'*eye(2*length(X_target))*A)\eye(6)*A'*eye(2*length(X_target))*(Y_linear2)';
   n=n+1;
   ksi0 = ksi0 + del_ksi;
   x0(i) = xp-c*Nomx(X_true(i), ksi0(1),Y_true(i),ksi0(2),Z_true(i),ksi0(3))/Den(X_true(i), ksi0(1),Y_true(i),ksi0(2),Z_true(i),ksi0(3));
   y0(i) = yp-c*Nomy(X_true(i), ksi0(1),Y_true(i),ksi0(2),Z_true(i),ksi0(3))/Den(X_true(i), ksi0(1),Y_true(i),ksi0(2),Z_true(i),ksi0(3));
   if Input == 'DSC00370.jpg'
        A = [jacobian([x0(1)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(1)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(2)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(2)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(3)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(3)-xp],[X0,Y0,Z0,omega,phi,kappa]);...
        jacobian([x0(4)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(4)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(5)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(5)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(6)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(6)-xp],[X0,Y0,Z0,omega,phi,kappa])];
   elseif Input == 'DSC00371.jpg'
        A = [jacobian([x0(1)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(1)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(2)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(2)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(3)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(3)-xp],[X0,Y0,Z0,omega,phi,kappa]);...
        jacobian([x0(4)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(4)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(5)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(5)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(6)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(6)-xp],[X0,Y0,Z0,omega,phi,kappa]);...
        jacobian([x0(7)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(7)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([x0(8)-xp],[X0,Y0,Z0,omega,phi,kappa]);jacobian([y0(8)-xp],[X0,Y0,Z0,omega,phi,kappa])];
   end

   for i = 1:length(X_target)
        Y_linear2(2*i-1) = [x(i)-x0(i)];
        Y_linear2(2*i)= [y(i)-y0(i)];
   end 
end
ksi


end

This is a part of my code. As i guess, it take so long because some variables keep changing during the while iteration.

In matlab, it shows an error message that certain variables are changing during the loop so that preallocation would help reducing the running time.

[dpb]

"This is a part of my code. ..."

n=1;
while (n<3);
   del_ksi = (A'*eye(2*length(X_target))*A)\eye(6)*A'*eye(2*length(X_target))*(Y_linear2)';
   n=n+1;
   ksi0 = ksi0 + del_ksi;
   x0(i) = xp-c*Nomx(X_true(i), ksi0(1),Y_true(i),ksi0(2),Z_true(i), ...

And not enough part, either..."i" is undefined in the above segment which appears to probably be where the problems start.

Just start with the editor messages and work your way through -- what is the range of i for the above code? You've bounded a variable n, but it's never defined nor incremented to stop the otherwise ifinite loop the while has created.

Definitely nothing anybody can help with with only this piece to look at.

Answer 1

[Gaurav Garg]

Hi,

What could be a problem here is -

You are assigning values to arrays which haven't been allocated any space beforehand.

For an example -

You may try to use this code

a = ones(1,10)
for i = 1:10
    a(i) = i;
end

rather than this one

for i = 1:10
   a(i) = i;
end

Some of the variables where you can pre-allocate space are -

1. y0
2. x0
3. Y_linear2

Note:

Probably, you are facing a warning and not an error. Your program would run perfectly fine even if you don't make the changes suggested.