Error iterating with fractions
5 views (last 30 days)
Show older comments
I want to do something pretty simple but am not sure how to do because I can't iterate using fractions. What I want is to solve for x(i), y(i), and z(i). All three are dependent on the previous value. I have attached an attempt to solve this below but naturally I can't iterate using fractions. My tf value is 3.5272 so naturally I want more than 3 or 4 iterations. Any ideas? I just want to solve the three equations for a time step of 0.1 and eventually plot it. I get an error in the line where I define x(i) saying "subscript must be either real positive integers or logicals."
theta = 50; % deg
phi = 0; % deg
u = 16; % m/s
u_x = u*cosd(theta)*cosd(phi);
u_y = u*sind(theta)*cosd(phi);
u_z = u*sind(phi);
x(1) = 0;
y(1) = 0;
z(1) = 60;
tf = 3.5272;
for i = 1.1:0.1:roundn(tf,-1)
x(i) = u_x*i + 0.5*ax*i^2 + x(i-0.1);
y(i) = u_y*i + 0.5*ay*i^2 + y(i-0.1);
z(i) = -u_z*i + 0.5*az*i^2 + z(i-0.1);
end
0 Comments
Accepted Answer
Stephen23
on 4 Apr 2017
Edited: Stephen23
on 5 Apr 2017
Fractions cannot be used as indices. Put the fractional values in a vector and make the indices integers:
vec = 1.1:0.1:roundn(tf,-1);
for k = 2:numel(vec)
val = vec(k);
x(k) = +u_x*val + 0.5*ax*val^2 + x(k-1);
y(k) = +u_y*val + 0.5*ay*val^2 + y(k-1);
z(k) = -u_z*val + 0.5*az*val^2 + z(k-1);
end
[edited based on comments below]
4 Comments
Les Beckham
on 4 Apr 2017
I suspect that is what Stephen intended. You will also need to change the for loop to start at 2 instead of 1 (so you don't try to index into x with a zero).
More Answers (0)
See Also
Categories
Find more on Elementary Math in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!