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How to add equation to function

Asked by Angel Hiram Torres Mota on 21 Jun 2019 at 2:33
Latest activity Edited by madhan ravi
on 21 Jun 2019 at 3:04
I need to add my equation (60+(2.13*(t^2))-(0.0013*(t^4))+(0.000034*(t^4.751))) to a function but I cant figure it out. What I've tried just comes out as an error. Please help.
k=1;
for t = 0:2:100;
h(k) = (60+(2.13*(t^2))-(0.0013*(t^4))+(0.000034*(t^4.751)));
k = k+1;
if h>=0
disp(h);
end
end
This is what I tried but it doesnt work.
k=1;
for t = 0:2:100;
h(k) = rocket(t)
k = k+1;
if h>=0
disp(h);
end
end
function h(k) = rocket(t)
h(k) = (60+(2.13*(t^2))-(0.0013*(t^4))+(0.000034*(t^4.751)));
end

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3 Answers

Answer by madhan ravi
on 21 Jun 2019 at 2:43
Edited by madhan ravi
on 21 Jun 2019 at 2:54
 Accepted Answer

Note: the following can be done trivially without a loop by vectorisation.
t = 0:2:100;
h=zeros(size(t));
for k=1:numel(t);
h(k) = rocket(t(k))
if h(k)>=0
disp(h(k));
end
end
function h = rocket(t)
h = (60+(2.13*(t^2))-(0.0013*(t^4))+(0.000034*(t^4.751)));
end
Without loop:
t = 0:2:100;
h = rocket(t);
fprintf('h >= 0:%f\n',h(h>=0))
function h = rocket(t)
h = (60+(2.13*(t.^2))-(0.0013*(t.^4))+(0.000034*(t.^4.751)));
end

  1 Comment

Exactly what I was looking for, thanks!

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Answer by Star Strider
on 21 Jun 2019 at 2:44

Except for your ‘rocket’ function, most of that looks as though it should work.
Leave out the subscript reference when you are declaring your function, and within your function, since ‘k’ is not defined within your function, and is not necessary anyway.
Try this instead:
function h = rocket(t)
h = (60+(2.13*(t^2))-(0.0013*(t^4))+(0.000034*(t^4.751)));
end

  2 Comments

I wish I could accept all of the 3 answers. Thanks for the help!

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Answer by Adam Danz
on 21 Jun 2019 at 2:51
Edited by Adam Danz
on 21 Jun 2019 at 2:58

Try using an anonymous function. I also cleaned up the for-loop so it is used properly.
rocketFcn = @(x)(60+(2.13*(x^2))-(0.0013*(x^4))+(0.000034*(x^4.751)));
tm = 0:2:100;
h = zeros(size(tm));
for t = 1:numel(tm)
h(t) = rocketFcn(tm(t));
if h(t)>=0
disp(h(t));
end
end
Note that I added ".^" to your rocket function. This allows you to apply vectors to its input so you can avoid the loop.
tm = 0:2:100
h2 = rocketFcn(tm);
% The two lines above produces the same output as the for-loop!
isequal(h,h2)

  2 Comments

No problem! You can implement the anonymous function I suggested in madhan ravi's solution as well.

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