Undefined function or variable 'impact'.

I'm having an issue with ubdefined variable I'm using 2015b.

I knew there's some veriable wont work on older version, is it because of the version of my matlab.

or did I miss something.

clc;
clear;
g = 9.81;
theta = 33;
vel = zeros(1,10);
tim = zeros(1,10);
AC = zeros(1,10);
i = 0;
for a_c = 1*g:g:10*g
    i = i + 1;
    AC(i)=a_c;
    I = impact(a_c,theta);
    vel(i) = I;
    tim(i) = 0.75/I;
end
figure
subplot(1,2,1)
ploy(AC,vel)
title('impact velocity vs acc.');
xlabel('acc');
ylabel('Velocity');
subplot(1,2,2);
ploy(AC,tim)
title('Time vs acc.');
xlabel('acc');
ylabel('Time');

Error:

Undefined function or variable 'impact'.
Error in Untitled8 (line 12)
    I = impact(a_c,theta);

[Walter Roberson]

impact() is not a Mathworks function that I can find. I also do not find it in any File Exchange contributions.

Looking at your code, I think you are expected to write the function yourself.

[Raad Alsulaiti]

that's good enough for me, thanks.