break out of for loop help

I have this for loop which works perfectly fine except that I want it to stop the for loop when y=0. The loop is calculating trajectory so I want it to stop when the ball hits the ground (or y=0). I have tried everything I can think of but nothing works. It either doesn't stop the loop or it returns the completely wrong y values. I've tried if y==0, y<=0, y(n)==0, y(n)<=0, y(n+1)==0, y(n+1)<=0, and putting it before and after the calculations. nothing worked Please help.

for n=1:N

    ax(n+1) = -D*vx(n)*v(n);
    ay(n+1) = -D*vy(n)*v(n)-g;
    v(n+1) = sqrt(vx(n)^2+vy(n)^2);
    x(n+1) = x(n)+T*vx(n)+0.5*T^2*ax(n);
    vx(n+1) = vx(n)+T*ax(n);
    y(n+1) = y(n)+T*vy(n)+0.5*T^2*ay(n);
    vy(n+1) = vy(n)+T*ay(n);
    if y(n+1)==0, break; end
end

[Jan]

Please post your initial values such that we can run your code.

[Sean Smith]

h=1;

C=0.5;

R=0.0366;

p=1.2;

m=0.145;

g=9.81;

D=C*p*pi*R^2/(2*m);

vo=90*0.44704;

th0=30*(pi/180);

Tmax=vo*sin(th0)/g+sqrt(2*h/g+vo^2*sin(th0)^2/g^2);

T=1/100;

t=0:T:Tmax;

N=floor(Tmax/T);

v(1)=vo;

x(1)=0;

vx(1)=vo*cos(th0);

y(1)=h;

vy(1)=vo*sin(th0);

ax(1)=-D*vx(1)*v(1);

ay(1)=-D*vy(1)*v(1)-g;

Answer 1

[Jan]

The loop does stop. You can check this by a disp statement before the break.

I assume you have written the code into a script and y is defiend from an earlier run. Then a "clear" statement on top would be helpful - not "clear all". Or you could convert it to a function by inserting this as first line:

function myIntegrator

or what ever your file is called.

Note: Using several commands in one line impedes debugging. You cannot set a breakpoint on the break command in:

if y(n+1)==0, break; end

But this would have revealed the problem.

[Sean Smith]

i didn't mean to hit answer accepted, oops.

how does it fill it with only 1 iteration? shouldn't it do it from 1 to N? what would you suggest to get it to stop when y=0?

Answer 2

[Image Analyst]

It probably won't hit 0.0000000000000000000 exactly. It might get to 0.000000000000002, so check if it's close:

if abs(y(n+1)) < 0.0001  % Some tolerance.
  break;
end

[Sean Smith]

still not stopping it for some reason