manage a list of instances of a class

hi everybody, i got some classes and for depending one of antoher or basicly there is one big class that contains the the other classes as properties. i woult like to write a function that manages me the

classdef node<handle
    properties
        x
        y
        bearing=0
    end % properties
    methods
        function K = node(x,y)
         %   if nargin == 0, return, end
            K.x=x;
            K.y=y;
        end%functions
    end%methods
end %class
in the main should be a variable nodelist that keepst track of all the instances of node. a new one ist created like this

nodelist = {};nodelist ={nodelist{:},node(1,2)}
i tried to write a function that can create and delete a node

function nodelist=addnode(nodelist,x,y)
     if exist(nodelist)==0
         nodelist={};
     end
    nodelist = {nodelist{:},node(x,y)};
end

>>addnode(nodelist,1,2)% should be called like this

but this doesnt work and i dont know why and i send a copy of nodelist to the function wich is probably a not very economic way because the could bee 1000 of nodes in a structure. how do i use a pointer in order to make it faster?

thanks a lot in advance

Answer 1

[Jacob Halbrooks]

You might want to use a PERSISTENT variable within nodelist() to keep track of the nodes. For example:

function varargout = addnode(varargin)

% Create a persistent variable to keep track of the nodelist
persistent nodelist;
if isempty(nodelist)
    nodelist = {};
end

% Add a node if given inputs
if nargin
    nodelist{end+1} = node(varargin{1},varargin{2});
end

% Return nodelist if requested
if nargout
    varargout{1} = nodelist;
end

This function lets you get, set, or get/set nodes:

>> addnode(1,2);
>> addnode(2,4);
>> nodes = addnode

nodes = 

      [1x1 node]    [1x1 node]

This may be a feasible lightweaght approach for your problem, but I'd also suggest thinking about the interface you want and considering something like a NodeList class with methods like addNode() and getNode(). That would enable you to completely hide the list data structure.

[jeff wu]

thanks a lot,

i thought about that too but i guess its gonna be a bit complicated in that case because i got the classes : beam, node, form, material and points, has all of them as properties

evrey beam has exactly 2 nodes, 1 material and 1 form, but it can have any given number of point. so i would need a nodelist, beamlist,meteriallist and a formlist. and snce every beam can have any given number of points i would need for every instance of beam a pointlist.

i hope you can follow me. i really dont know yet how to organize the programm

Answer 2

[Daniel Shub]

Your node list seems to me to be related to the doubly linked list example: http://www.mathworks.co.uk/help/techdoc/matlab_oop/f2-86100.html#brikpee

As for pointers, MATLAB does not need pointers since its memory management is pretty dang smart. Basically, all "variables" in MATLAB are pointers, MATLAB keeps track of all the references to a variable and only allocates new memory if you change a variable that has another reference to it. For example, look at the memeroy usage when you do:

x = randn(1e8, 1); % Big jump
y = x; % No change
y(1)=0; % Big jump

[jeff wu]

thanks a lot,

i thought about that too but i guess its gonna be a bit complicated in that case because i got the classes : beam, node, form, material and points, has all of them as properties

evrey beam has exactly 2 nodes, 1 material and 1 form, but it can have any given number of point. so i would need a nodelist, beamlist,meteriallist and a formlist. and snce every beam can have any given number of points i would need for every instance of beam a pointlist.

i hope you can follow me. i really dont know yet how to organize the programm

[Daniel Shub]

You have accepted an answer and posted an identical comment to both answers. It is unclear if you question is answered or if there is a new question ...

Also, it is better to convey "thanks a lot" by voting for questions and answers which is done by clicking the triangle near the avatar.