I need some help getting my loop to work, I'll post a full script below, Thanks in advance.

if true
  % code
end
Do = 15;   % diameter of die inlet [mm]
D1 = 9;    % diameter of die outlet [mm]
Eps = 300;  % strain hardening exponent [N/mm^2]
u = 0;     % friction coefficient
Yo = 250;  % yield stress [n/mm^2]
x(1) = 0;
sigma_x(1) = 0;
D(1) = Do;
Y(1) = Yo;
p(1) = Yo;   % die pressure
alpha = 12*(180/pi);
n = 10;          % number of slices
dD = (Do-D1)/n;  % step size
dx = (dD)/(2*tan(alpha));
for count=1:n
  dsigma_x = (2/D)*(sigma_x + (Y-sigma_x)*(1+u*cot(alpha)))*dD;
  sigma_x(count+1) = sigma_x(count)+dsigma_x;
  D = D-dD;
  strain = 2*log(Do/D);
  Y = Yo + Eps*strain;
  p(count+1) = Y - sigma_x(count+1);
  x(count+1) = x(count)+dx;
end
figure(1)
plot(x, sigma_x)
xlabel('x')
ylabel('y')
figure(2)
plot(x, p)
xlabel('x')
ylabel('y')

Answer 1

[KSSV]

Do = 15;   % diameter of die inlet [mm]
D1 = 9;    % diameter of die outlet [mm]
Eps = 300;  % strain hardening exponent [N/mm^2]
n = 10;          % number of slices
u = 0;     % friction coefficient
Yo = 250;  % yield stress [n/mm^2]
x(1) = 0;
sigma_x(n,1) = 0;
D(1) = Do;
Y(1) = Yo;
p(1) = Yo;   % die pressure
alpha = 12*(180/pi);

dD = (Do-D1)/n;  % step size
dx = (dD)/(2*tan(alpha));
for count=1:n
    dsigma_x = (2/D)*(sigma_x(count) + (Y-sigma_x(count))*(1+u*cot(alpha)))*dD;
    sigma_x(count+1) = sigma_x(count)+dsigma_x;
    D = D-dD;
    strain = 2*log(Do/D);
    Y = Yo + Eps*strain;
    p(count+1) = Y - sigma_x(count+1);
    x(count+1) = x(count)+dx;
end
figure(1)
plot(x, sigma_x)
xlabel('x')
ylabel('y')
figure(2)
plot(x, p)
xlabel('x')
ylabel('y')