How can I plot my function?

My program is supposed to plot a function, but every time I try this I either end up with an empty plot or with an error. The code is this:

function Q = hydrogenusage(P)
Q = (120*P)-(P^2);
plot(P,Q)
xlabel('Power')
ylabel('Usage')
title('Hydrogen usage')
grid on
end

The error I get is 'Not enough input arguments'. Okay, I thought, it needs some kind of input. So I entered:

hydrogenusage(0)

But if I try that it gives me an empty plot. I tried varying the 0 value I added as input, but it didn't work. How can I make this work?

Answer 1

[Youssef Khmou]

You need to provide a vector as the input to get a result of the equation Q , but you need to use element wise operations , alter your function :

 function Q = hydrogenusage(P)
  Q = (120*P)-(P.^2);
plot(P,Q)
xlabel('Power')
ylabel('Usage')
title('Hydrogen usage')
grid on
end

[N/A]

Thank you! It worked. But can I make it so that I just have to type in 'hydrogenusage' (so not hydrogen (0:120) ? I tried using:

axis([xmin xmax ymin ymax])

But alas, that only sets the limits of the axis itself. I'd like to preset the number of data points it should calculate before plotting. Is that possible?

[Youssef Khmou]

the question is not clear yet, you mean a function without input? or only axis adjustment ? inside the function put this line :

 axis([P(1) P(end) Q(1) Q(end)])

Answer 2

[Walter Roberson]

It is plotting, but it is only plotting a single point because you only asked it to plot a single point. You need to pass in a vector of points such as

hydrogenusage(0:10)

You will find you also need to change P^2 to P.^2