Use of handle in matlab 2013b

hi

I am wondering whether I can use the handle function in my functions when I am using matlab 2013b.

[Adam]

Which handle function? I am not aware of one, even in R2018b

[Muazma Ali]

I am not sure whether I should call it a function.

as part of a function, its possible to use "handle" as output of a function where one if the reason is to accumulate some values.

[madhan ravi]

illustrate with an example what you mean

[Adam]

If you use your offline inistalled documentation it will tell you what syntaxes of functions are available in your version, e.g.

doc plot

will show that you can return a plot handle and then use it to manipulate the plotted line afterwards.

[Muazma Ali]

Hi Madhan Ravi!

Here comes the example:

function h= counter
x=0;
h=@addone;
   function y=addone;
    x=x+1;
    y=x;
end 
end

......

Can this be done in Matlab2013b?

[Adam]

function h = counter
x=0;
h=addone;
   function y=addone
    x=x+1;
    y=x;
end 
end

with a couple of corrections from what you wrote is valid Matlab syntax and will run. It will return 1 every time though. I doubt that is what you actually want it to do.

Don't use @ unless you are defining a function handle. Here you are just calling a function.

[madhan ravi]

"Don't use @ unless you are defining a function handle. Here you are just calling a function."

h=@addone; % function invoked
h(0)

function y=addone(x);
    x=x+1;
    y=x;
end 

[Muazma Ali]

well there is nothing wrong with the code I think..it was taken from a book.

[Muazma Ali]

well x is the local variable in the main function that the sub function can change..then I think therefore it is no need to have this as input variable

Answer 1

[madhan ravi]

%%%% The below can be in a command window or in a separate script file
h = counter ; % function call
h(0)
% ^----- x is zero , I suggest you to keep x as input so you can change it whenver you call the function

%%%%% The below should be saved as in a separate file named counter.m since you are using 2013b
function h = counter
h=@addone;
   function y=addone(x);
    x=x+1;
    y=x;
end 
end

See https://www.mathworks.com/help/matlab/matlab_prog/nested-functions.html#f4-64094

[madhan ravi]

So if you like to keep your original function then either:

function h= counter % parent function
h=@addone;
    function y=addone;  % nested function
    x=0; % define x inside nested function
    x=x+1;
    y=x;
end 
end

[madhan ravi]

Muazma Ali's answer moved here:

i think u misunderstood..evry time I call h() the value will be increased by 1 and accumulated..that was what I need for my purpose..I am not interested in sending my value.

for instance the purpose if of counting the times one procedure has run

[madhan ravi]

Can you show where you are going to use it to count the number of times ? if so recursive call could suffice your need.

Answer 2

[Adam]

function h = counter

persistent x

if isempty( x )
	x=0;
end
h=addone;
   function y=addone
     x=x+1;
     y=x;
   end 
end

would work, though it is an ugly way to program such functionality in general.

Answer 3

[Guillaume]

Does R2013b support function handles? Yes. Function handles have existed since before R2006a.

Irrespective of that Is it a good idea to create a function that return a self-incrementing variable on each call? Absolutely not. While it can be done using persistent variables (see adam's answer), this is antithetical of matlab design philosophy. The traditional way is to pass the variable to be incremented as input and return the incremented variable as output. Only under very rare circumstances should functions have internal state (and if so, a handle class would probably be better).