I'm struggling to plot this graph

I have this equation

with the variables

and i'm trying to get this plot

I keep getting a straight line.I'm not sure what I have done wrong.

Can anyone help me and copy and paste the input which is needed to form this plot.

thanks for the help in advance.

Answer 1

[Star Strider]

This plots correctly for me:

aeq = @(T,Ts,dT,a) a(1) - 0.5*a(2).*(1 + tanh((T - Ts)./dT));

a = [0.58; 0.47];
Ts = 283;
dT = 24;
T = linspace(250, 310);

figure(1)
plot(T, aeq(T,Ts,dT,a))
hold on
plot(288, aeq(288,Ts,dT,a), '+r')
hold off

[Hoi Tsim]

thanks a lot for your answer. Helped very much!

[Star Strider]

My pleasure!

If you want to calculate the value of ‘T’ corresponding to aeq=0.3, use the fzero function:

Ta3 = fzero(@(T) aeq(T,Ts,dT,a)-0.3, 1)

Ta3 =
   287.6532

[Hoi Tsim]

thanks! I'm struggling because I'm doing a maths project but never used matlab and plotted these sorts of functions before.

[Hoi Tsim]

I've also got another 2 graphs which include plotting 2 curves in the same graph and another really difficult one. Hopefully someone helps me.

[Star Strider]

My pleasure!

To plot 2 (or more) curves on the same plot, the easiest way is to use the hold function:

figure(1)
plot(x, y1)
hold on
plot(x, y2)
hold off
grid

[Hoi Tsim]

I'm not sure what you mean.. could you look at my links and try help me..

http://www.mathworks.com/matlabcentral/answers/248947-help-with-plotting-graph-plotting-multiple-lines-with-equations

http://www.mathworks.com/matlabcentral/answers/248948-how-to-plot-this-graph-with-given-values-and-equations

[Star Strider]

I looked at those, but cannot figure out what Q is. you need to know what it is or how to calculate it before you can proceed. (Meteorology and Climatology are not areas of my expertise. I know what albedo is, but I am not familiar with those equations.)

[Hoi Tsim]

thanks very much for having a look!

[Star Strider]

My pleasure!

[Hoi Tsim]

i have looked at my notes and i see that σ = 5.670367 × 10-8 kg s-3 K-4

does this help with continuing the question?

do i just set it out like the first plot you helped me with, defining each equation and then after >> figure i type.. plot(T, aeq(T,Ts,dT,a),Ri,Ro)?

[Star Strider]

I still don’t know what Q is, or how to calculate it. (It seems to be a variable, and could be either data a function. It is necessary to calculate at least one other variable in your other two Questions, and in one is the essence of the Question.)

Sorry, but full stop until I get a definition for Q!

Answer 2

[Thorsten]

a1 = 0.58;
a2 = 0.47;
Tstar = 283;
dT = 24;
aeq = @(T) a1 - 0.5*a2 *(1 + tanh((T-Tstar)/dT))
T = 250:310;
plot(T, aeq(T))

[Hoi Tsim]

thanks very much for your answer! loads of help