Creating a function to calculate yield strength of a metal?

I am working on the following problem.

This is the code i have so far.

if true
  % code
grain_size = 0.1;
strength_vector = zeros(1,20);
n = 1;
while (grain_size < 2.0)
  A = HallPetch(12000, 9600, grain_size);
  strength_vector(n) = A;
  n = n + 1;
  grain_size = grain_size + 0.1;
end
M = (0.1: 0.1: 2.0);
M = M';
strength_vector = strength_vector';
fprintf('Grain Size (mm)      Yield Strength(psi) \n');
fprintf('%5.1f %25.3f \n', [M, strength_vector]');
function [yield_strength] = HallPetch(sigma_nought, k, d)
yield_strength = sigma_nought + k*(d^(-1/2));
end
end

It seems to work up until the grain size equals 2.0, then the result it gives me is zero. Any ideas why?

Answer 1

[Ameer Hamza]

Since you want to get the value up to 2 you need to increase the limit of while loop a little bit

while (grain_size < 2.01)

Now it will run for grain_size=2

Grain Size (mm)      Yield Strength(psi) 
0.1                 42357.866 
0.2                 33466.253 
0.3                 29527.122 
0.4                 27178.933 
0.5                 25576.450 
0.6                 24393.547 
0.7                 23474.195 
0.8                 22733.126 
0.9                 22119.289 
1.0                 21600.000 
1.1                 21153.241 
1.2                 20763.561 
1.3                 20419.757 
1.4                 20113.481 
1.5                 19838.367 
1.6                 19589.466 
1.7                 19362.864 
1.8                 19155.418 
1.9                 18964.572 
2.0                 18788.225

Note you cannot use

   while (grain_size <= 2)

because of finite precision of floating point.

[James]

Awesome thank you!

[Ameer Hamza]

You are welcome!