While loops within a for loop not terminating

The code below is not working and I can't work out why. Each of the while loops work by themselves but stop working in the for loop.

THE CODE;

function output = A1C_z3285824(N,d_theta,animFlag)

%declare constants
th12 = pi/4;
a2 = 180;
a3 = 590;
a4 = 300;
a5 = 330;
a7 = 450;
a8 = 500;
x_a0b0 = 520;
y_a0b0 = 200;
x_a0d0 = 420; %#ok<NASGU>
y_a0d0 = 50;
q = 1;

iterations = floor(N*360/d_theta);

for Z = 1:iterations;

%iterate for th14
e1 = 0.1;
dif1 = 1;
th14 = pi/4;

      while dif1>e1
      x = acos((x_a0b0+a2*cos(th12)-a4*cos(th14))/a3);
      y = asin((y_a0b0-a2*sin(th12)-a4*sin(th14))/a3);
      dif1 = x-y;
      dif1 = abs(dif1);
      th14 = th14+0.1;  
      end

th13 = x;
th15 = asin((y_a0b0-a4*sin(th14))/a5);
s6 = x_a0b0 - a4*cos(th14) - a5*cos(th15);

%iterate for th17
e2 = 0.1;
dif2 = 1;
th18 = 3*pi/2;

      while dif2>e2
      m = acos((abs(s6)+x_a0b0+a8*cos(th18))/a7);
      n = asin((y_a0d0+y_a0b0+a8*sin(th18))/a7);
      dif2 = m-n;
      dif2 = abs(dif2);
      th18 = th18+0.1;
      end

th17 = m;
Gx = a7/2*cos(th17) - s6;
Gy = y_a0b0 + a7/2*sin(th17);

%print to array
A = zeros(9,iterations);
A(1,q) = th12;
A(2,q) = th13;
A(3,q) = th14;
A(4,q) = th15;
A(5,q) = th17;
A(6,q) = th18;
A(7,q) = Gx;
A(8,q) = Gy;
A(9,q) = s6;

%increase q and th12 for next iteration
     th12 = th12+d_theta;
     q = q+1; 
end

%write to structure
theta_12 = A(1,:);
theta_13 = A(2,:);
theta_14 = A(3,:);
theta_15 = A(4,:);
theta_17 = A(5,:);
theta_18 = A(6,:);
G_x = A(7,:);
G_y = A(8,:);
s_6 = A(9,:);

output = struct('THETA12', theta_12, 'THETA13', theta_13, 'THETA14', theta_14, 'THETA15', theta_15, 'THETA17', theta_17, 'THETA18', theta_18, 'Gx', G_x, 'Gy', G_y, 'S6', s_6);
end

Answer 1

[Oleg Komarov]

For example:

N = 2 
d_theta = 360

the second loop diverges, i.e. dif2 increases and th15 is imaginary.

Check the steps in between the loops.