Basic matlab q on writing error messages

[brandy]

How do you write error messages
for when a function has been given an input that is illogical for what the function does.
in matlab

function b = bla(a)
for example if a < 0
i want it to display a message

 

[jhae2.718]

You could do something as basic as printing a string when the error occurs, e.g.:

function [output] = myfun(input)
    % do stuff
    if someCondition < minValue % define error condition however you need it
         fprintf('Error: invalid input. Input must be between foo and bar!\n');
         return;
    end
end

A better way would be to http://www.mathworks.com/help/techdoc/matlab_prog/bq_jgj8-1.html" . This way, any code that calls the function can handle errors.

function [output] = myfun(input)
    % do stuff
    if someCondition < minValue % define error condition however you need it
        err = MException('Myfun: Input Error', ...
                         'Myfun received bad input arguments.');
        throw(err);
    end
end