Confused about Static class methods versus normal functions, and their speed

Hi all,

Maybe I understand classes wrong, but the following code illustrates the issues I see:

classdef my_class
    methods (Access = public, Static = true)
        function N = N_intern
            N = 3;
        end
        function N = calc_intern
            N = my_class.N_intern;
        end
        function N = calc_extern
            N = N_extern;
        end
    end
    methods (Access = public)
        function go(obj)
            tic
            for i = 1:1e3
                obj.calc_intern;
                obj.calc_intern;
                obj.calc_intern;
                obj.calc_intern;
                obj.calc_intern;
                obj.calc_intern;
                obj.calc_intern;
                obj.calc_intern;
            end
            toc
            tic
            for i = 1:1e3
                obj.calc_extern;
                obj.calc_extern;
                obj.calc_extern;
                obj.calc_extern;
                obj.calc_extern;
                obj.calc_extern;
                obj.calc_extern;
                obj.calc_extern;
            end
            toc
        end
    end
end

function N = N_extern
    N = 3;
end

The way I see it:

• From a normal public method, I can call a Static method like obj.calc_intern
• Within calc_intern, I can only call another Static method if I use the classname : my_class.N_intern

Now I have 2 choices if I have a functions that does not use class properties, but clearly belong to the functionality of the class:

1. I can make them Static methods, but then I have to use the classname if Static methods call other Static methods.
2. I can make them normal functions, outside the class (like N_extern in my example)

In my example, the first option is 3 times slower than the second option. Apparently MATLAB constructs a new class for each call my_class.N_intern? Given the meaning of 'Static' a new instance of the class is not needed I would say...

So for speed considerations you should not use Static methods this way, but simply make them normal functions outside the class. Or am I missing something?

Best regards,

    Jeroen

Answer 1

[Titus Edelhofer]

Hi Jeroen,

here the MATLAB version used really make a difference: the new engine in R2015b performs much better. On my machine I get:

R2014b:
Elapsed time is 0.143644 seconds.
Elapsed time is 0.090536 seconds.

So roughly factor 1.5.

But with R2015b I get

Elapsed time is 0.003158 seconds.
Elapsed time is 0.003184 seconds.

So both versions MUCH faster, and no overhead for the "intern" any more ...

Titus

[Jeroen Boschma]

Thanks Titus.

This points me in the right direction. I now see that R2015b indeed has a new execution engine, and MathWorks claim to have optimized function call overhead and many OOP things. Apparently it works out very well on this issue. I'll try to find some more in-depth information on their new execution engine.