MATLAB: I am trying to write a function.

function

for example i want to calculate the area of a triangle. so i will use the formula 1/2(b*h). and i also want to calculate volume of a triangle and i will use 1/2(b*h*l). so when i am passing the base(b) and the height(h), i want it to give me the area, and when i am passing the base(b), height(h) and length(l) i want it to give me the volume. i want to use function for my input arguments. How can i do it?

Best Answer

A small example code:

function r = Calculate(a, b, c)
switch nargin
  case 2
    disp(a)
    disp(b)
    r = a * b;
  case 3
    disp(a)
    disp(b)
    disp(c)
    r = a * b + c;
  otherwise
    error('2 or 2 inputs required');
end

If you do not know how many inputs the function will get, use varargin. See

doc nargin
doc varargin

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MATLAB: Experts of MATLAB, how did you learn? Any advice for beginner/intermediate users

I reject the label "expert", but here is my two cents worth anyway:

MATLAB Specific:

MATLAB has a great feature that very few programming languages have: readable documentation. Use it! Search it using your favorite internet search engine. Practice browsing it via the contents on the left-hand side (which are all hyperlinks). Understand how it is grouped by topic. Try out the examples. Use the help to locate related functions and advice on how to solve particular problems.
Read the help for every function and operation that you use, no matter how trivial you think that operation is. Half of the questions that we answer on this forum are solved by reading the documentation for the function/operator that the user is already using!
Learn to use the debugging tools. These are indispensable. Read about how they work and what they do, then practice using them! For starting debugging, the most useful command is: dbstop if error
Learn the differences between array and matrix operations, otherwise your calculations will simply produce nonsense and you won't know why. If you are not doing linear algebra you need array operations.
Learn about comma-separated lists, and the easy ways to use them.
Pay attention to all of the code warnings, error messages, underlining, and tips that the MATLAB Editor shows. Do not ignore these messages.
Make vectorized code your first choice when writing code, and leave those ugly low-level loops behind you... Understand why vectorized code is beautiful, and how it can be used to make your code much more efficient and easier to understand.
And of course when loops are required, always preallocate the arrays before the loops.
There are important ways to write fast and efficient code. Use them.
For example, use absolute or relative filepaths instead of slow and hard-to-debug cd.
Learn good MATLAB programing habits right from the start, because life is too short to un-learn bad habits! This means: comment your code, use consistent formatting, write help (with H1 line) in every function, pass variables properly, use input checking, never use eval (or assignin, feval, etc), etc.
Do not force meta-data (e.g. dates, times, indices, test parameters, etc) into variable names or fieldnames: meta-data is data, so store it as data in an array.
Use subs to substitute values into a symbolic expression and evaluate it. Do not use eval to do this, it is not the correct tool for the job!
Write functions, not scripts. Scripts are good for playing around with, but not for real work.
Refer to all graphics objects (figures, axes, lines, etc) using explicit handle references (e.g. using Parent property). This makes plotting and handling graphics robust and predictable. Do not assume that the current figure/axes/etc is going to be the one that your code needs to access.
Pass variables reliably using input/output arguments and do not use globals or assignin. If you need to pass lots of values (e.g. simulation parameters) then put them into a structure and pass that.
MATLAB blogs are an excellent source of inspiration and ideas. Loren Shure's blog is a mine of great ideas, and a veritable pleasure to read too.
Check out other people's code on File Exchange (FEX). Note that the comments are often more useful than the ratings... and you will soon get an idea of whose comments are particularly worth paying attention to.

General Advice:

Imagine that every script and function you write is going to be given to someone else... impress them!
Test everything thoroughly. Check each line as you write it. Does it really do what you think it is doing? Many beginners come here to ask for help because they only think about what they want their code to be doing, but never bother to actually check what their code really is doing. Code cannot read your mind.
Make a set of test-cases and collect all of the instances that fail while the code is being written, plus all the edge-cases and every case category that it needs to work with. You will not regret doing this.
Break problems into parts, solve the parts separately. Make functions for code that needs to be repeated: this allows code to be reused, and bug-fixed in one location. Scripts are great for quickly testing an idea, but functions are much more robust for anything that will be used for more than one day.
Think about what you are doing: actually think. What is the problem being solved? What is really the problem? How can it be solved? With what methods? Read Pólya's excellent book How To Solve It.
Don't get stuck believing that you have found the best solution... there can be a much better solution waiting just around the corner, that may just require a new perspective, a reformulation of the problem, or a slight rearrangement of the data.
Practice! Challenge yourself with tasks you want to solve, or take part in onlne code challenges or tutorials.

MATLAB: Cant see the line in the plot

Don't use plot if you are trying to plot each H vs V value. Use Scatter

for H=200:100:36000  
    Height(H) = H;
    Gc = 398000.5;                                                           %Gravitational Constant times Earth's Mass
    Re = 6371;                                                               %Radius of Earth
    V = sqrt(Gc/(Re+H));                                                     %Formula for calculating the Satellite Speed
    scatter(H, V);    
    hold on                                                                 %Allows to plot multiple times on the same graph
                                                                            %Plot the Height with respect the Speed
end
ylabel('Orbital Speed (Km/S)'), xlabel('Height (Km)')                       %Labels on each axis
grid on

A more effifient way, and the better answer is this:

clear all;
figure;
Gc = 398000.5;                                                        
Re = 6371;
cntr = 1;
for H=200:100:36000
    V(cntr) = sqrt(Gc/(Re+H))
    Height(cntr) = H;
    cntr = cntr + 1;
end
plot(Height,V)
ylabel('Orbital Speed (Km/S)');
xlabel('Height (Km)');
grid on;

The problem in your script is that you are plotting a single point, rather than a set of x&y values. Scatter plots a single point better.

The second bit of code is most likely what you are looking for.

Best Answer

Related Solutions

MATLAB: Experts of MATLAB, how did you learn? Any advice for beginner/intermediate users

MATLAB: Cant see the line in the plot

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