Save data from for loop without subscript index

I am programming a simulation of a falling object and I want to plot its trajectory. When plotting I experience the problem that the data is not stored.

I want to plot h as function of t without its data being overwritten.

I also want the steps in each iteration to be 0.1, so indexing will not work.

The standard solution for these plots is using 'indexing' h(t). This does not work because the subscript index 't' starts with '0' and has steps of 0.1.

My code:

t0 = 0; %start time is 0 sec.
dt = 0.1; % timestep is 0.1 sec.
t_stop = 10; % time stops at 10 sec if h=0 has not been reached.
h0= 30; %start height
g = 9.81; %gravitational constant.

for t = t0:dt:t_stop %starttime:timestep:stoptime
h= h0-0.5*g*(t)^2; %h as function of t
if h=<0    %stop simulation when h=<0
    break  
end
end

Question: how to plot 'h' as function of 't'?

Answer 1

[Guillaume]

%... constant definitions

timesteps = t0:dt:t_stop;
h = zeros(size(timesteps));  %preallocate h
for step = 1:numel(timesteps)
    t = timesteps(step);
    h(step) = h0-0.5*g*t^2;  
    if h(step)<= 0
        break;
    end
end

Note that the whole thing can be done without a loop:

%... constant definitions
t = t0:dt:t_stop;
h = h0 - 0.5*g*t.^2;  %note the .^ since t is a vector

[Mike Mierlo van]

This is not a working solution:

I want to plot 'h' as a function of 't', but it has to stop when the condition h<=0 is met.

This answer keeps running until t=t_stop, in that way 'h' can be negative which is faulty.

[Guillaume]

The loop stops as soon as h is negative. You can then shorten the vectors if you so wish (otherwise it's just 0s)

%... constant definitions
timesteps = t0:dt:t_stop;
h = zeros(size(timesteps));  %preallocate h
for step = 1:numel(timesteps)
    t = timesteps(step);
    h(step) = h0-0.5*g*t^2;  
    if h(step)<= 0
        break;
    end
end
tokeep = h > 0;
plot(timesteps(tokeep), h(tokeep));

You can do the same with the vectorised method

%... constant definitions
t = t0:dt:t_stop;
h = h0 - 0.5*g*t.^2;  %note the .^ since t is a vector
tokeep = h > 0;
plot(t(tokeep), h(tokeep));
%optional:
t = t(tokeep); 
h = h(tokeep);

[Mike Mierlo van]

Wow, You da man!

Thank you very much