Take a deep breath, you are doing just fine!
"I don't know what's wrong and even I did, I doubt I'd know how to fix it."
Here are two really important skills that you should start practicing:
- read the documentation for every function and command that you are using.
- check and test that every line does exactly what you need it to, before moving on to the next line. This means run it and check its output using different test cases.
If you had done these two steps then you would have learned that your very first line of code
D=(Dmin:Dmax:50);
does not help you to solve your task, and does not do what you think it does. Lets have a look:
>> D = 1.6:2.6:50;
>> numel(D)
ans = 19
When you read the colon documentation you will find out why this does not produce fifty values. You can also experiment in the command line, just like I did. You would also learn why this command is not suitable for this task, and when you would scroll to the bottom of that help page you would find some links to other functions... taking a few minutes to read each of their descriptions, you would find that linspace does exactly what you need:
D = linspace(...);
"where does the second, green line come from?"
Once again, if you had read the plot documentation then you would know the answer to this: there is no second green line. That plot contains just one line, which is green and has blue diamond markers. The plot documentation gives plenty of examples of how lines have colors, thicknesses, markers, and other options to pick from: there is only one line.
"How does the fact that the function has two outputs play into this?"
It plays absolutely no part in the plotting, but presumably (you do not say) you have to submit your work to get assessed or marked, in which case the outputs will likely be used to check that your function implements the formula correctly.
"How do I establish the difference for the functions for Tmin and Tmax?"
It is not clear why you want to get Tmax, because the assignment only asks you for Tmin. And once again, a little internet search for "MATLAB minimum" finds you the correct function (hint: min). And when you read its help you will find that it also returns an index as its second output, which you can use to get the D value corresponding to the Tmin value.
"Am I supposed to be checking for imaginary numbers and/or excluding them? How do I do that? Am I supposed to be checking them for min and max? If so, how do I do that?"
The assignment does not ask for any of this. Do not invent unnecessary complicating obstacles. Focus on the given task. If there was a need to deal with imaginary numbers then the assignment would mention it to be sure, or you could deal with it when it occurs.
Summary
Always read the documentation for all commands, no matter how trivial. Always check your code by hand: experimenting and trying things out is easy to do, and it does not cause your computer to explode if you make a mistake.
Do not just write code and hope that it is correct: code does not care what you think/wish/imagine/believe/want it to be doing. Code does not read your mind. You have to check what the code is actually doing.
For more tips and useful suggestions on how to learn how to use MATLAB efficiently:
