How to find undefined matrix in a code?

Hello everyone, i have a matrix that presents the alarmed devices in the coverage of an access point , but i dont have alarmed devices for all access point covarege area, and you know at that time the matrix for alarm is undefined, totally empty matrix so i can't use it in the following steps. What i am asking is : is there any way to write an if statement saying if that matrix is defined do that, if it is undefined do another thing. Can you help me please?

Answer 1

[James Tursa]

If the variable is not defined at all, you can use this:

if( exist('variable_name','var') )
    % variable_name is defined
else
    % variable_name is not defined
end

If the variable is in fact defined but is actually empty, do this instead:

if( isempty(variable_name) )
    % variable_name is empty
else
    % variable_name is not empty
end

[Cladio Andrea]

Just perfect , the second one actually is what i want. Thank you so much !!

[Guillaume]

In that case, for reference, the matrix is actually defined (i.e. the variable has been declared). The proper term is that it is empty (hence why you use isempty).