I am getting the following error for the below code: Subscript indices must either be real positive integers or logicals. How can i remove that error.

clc

clear all

g=9.81;

u=10;

t=0:.1:10;

y(1)=0;

while (y(t)>=0)

y(t)=(u*t)-(0.5*g*t.*t)

end

[Sattik Basu]

i found a different solution to this:

g=9.81;

u=100;

t=0;

y=0;

while (y>=0)

      disp(['at t=', num2str(t) ', the height is=', num2str(y)])
      t=t+0.1;
      y=(u*t)-(0.5*g*t^2);

end

why does this work and not the first one?

Answer 1

[Walter Roberson]

You have

t=0:.1:10;

so t is a vector containing 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0

You have

while (y(t)>=0)

but t is the vector discussed above, so your line is equivalent to asking

while y([0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0]) >= 0

However, this attempts to subscript y with 0 and non-integers.

I suggest you have a look at https://www.mathworks.com/matlabcentral/answers/353353-how-can-i-use-interval-with-decimal-at-the-end-of-a-count-in-for-loop-e-g-t-1-1-18-7#comment_478299