Plot function with changing variables

for v = 5:20 d = 20:120
w = (0.25*pi*(d.^2)*0.5*(v.^2))
plot(v,w)
hold on

end


% I am trying to plot v on the x axis, w on the y and vary the variable v between 5 and 20 and d between 20 and 120. I am new to Matlab why won't the graph appear? It just shows a blank white sceen?

Answer 1

[Star Strider]

The plot function plots lines between two points. You appear to be plotting points, so you need to plot markers.

Try this:

for v = 5:20
    for d = 20:120
        w = (0.25*pi*(d.^2)*0.5*(v.^2));
        plot(v,w,'.')
        hold on
    end
end

Experiment to get the result you want.

[Katie Fox]

Thank you, is there a way to connect the points for a given value for d? I am hoping to end up with 120 lines based on the variable d?

[Star Strider]

As always, my pleasure!

‘I am hoping to end up with 120 lines based on the variable d?’

Try this:

d = 20:120;
v = 5:20;
[V,D] = ndgrid(v, d);
w = @(v,d) (0.25*pi*(d.^2)*0.5.*(v.^2));

figure
plot(D, w(V,D))
xlabel('d')
ylabel('w')

Note that here ‘d’ only has 101 values, not 120.

Experiment to get the result you want.