Index of zero error

Hello, whenever I use this function to try to solve for the variables I get an error saying that I am trying to take the index(0) of a function. I have looked this thing up and down and cant find where its getting zero from, any help would be appreciated I am kind of new to MATLAB.

function R
g=9.8; alpha=((45*pi)/180);
v0=180;
cd=0.007;
[x, y]=ode45(@projectile,[0,-300],[v0*cos(alpha) v0*sin(alpha) 0 0]',[],v0,cd,g);
N=length(x);
indx=find(y(:,3)>0);
height=@(v,x,y) (-spline(x,y,v));
opt = optimset('display','off');
xmax=fminbnd(height, 0, 1000, opt, x, y(:,3));
ymax=-height(xmax, x, y(:,3));
disp(['ymax = ' num2str(ymax) ' m at x = ' num2str(xmax) ' m']);
xe = interp1(y(indx(end)-5:N, 3), x(indx(end)-5:N), 0);
te = interp1(y(indx(end)-5:N, 3), y(indx(end)-5:N, 4), 0);
disp(['Travel distance = ' num23str(xe) ' m and time of travel = ' num2str(te) ' s'])

function p=projectile(x, z, v0, cd, g)
v = sqrt(z(1)^2+z(2)^2);
if v < v0*1e-6
  error('Initail velocity not large enough, Increase')
end
p = [-cd*v; -(g+cd*v*z(2))/z(1); z(2)/z(1); 1/z(1)];

Answer 1

[Sean de Wolski]

indx=find(y(:,3)>0);

when there are no y(:,3)>0 indx is empty and thus its 'end' ( indx(end)) is indx(0) which doesn't exist!

what you should do here is add an isempty if statement before the interpolation

if isempty(indx)
  error('doh!') %or whatever
else
  what you have now
end

Also, it's worth your time to learn to use the debugger.

dbstop if error

will point you right to it.

[Joseph]

Okay I get what your saying but that doesnt really help, although thanks for locating the problem. Why are there no y(:,3)>0? there should be because I got the values from the ode45 command and it should have the positive values in it.

[Joseph]

Actually nevermind, I found out why there were no y(:,3)>0. In the ode45 function is should have been 300 not -300. Thanks for your help.