Optimizing code run time

Hi All,

I've the following function

function fun1()
            [t,x] = ode15s(@(t,s) fun2(t,x), tspan , x0 ,options);
            % other functions
end
function dx = fun2(t,x)
M = load(fullfile(path,'M.mat'));
:
:  
dx = M*x   
end

Each time fun2 is called, the same file is loaded and this increases the compute time

(calls: 52085 total time:156.848s, self time:59.780s). Of the total time taken (209s), 156s is taken for executing fun1 and 95% of the time is spent in loading the input file.

I'd like to ask for suggestions on how to get around this i.e reduce the time taken for loading/avoid loading for each function call.

Answer 1

[per isakson]

Try to replace

M = load(fullfile(path,'M.mat'));

by

persistent M
if isempty(M)
    M = load(fullfile(path,'M.mat'));
end

and see persistent

[Deepa Maheshvare]

Thank you, how can I deal with it if I am loading M.mat in the following way from a class named utils

M = utils.get_M;
function M = get_M
    M = load(fullfile(path, 'M.mat'));
end

Here, I couldn't do

M = utils.get_M;
function M = get_M
    persistent M
    if isempty(M)
        M = load(fullfile(path,'M.mat'));
    end
end

[per isakson]

You provide too little context to know for sure. And you diverge from the original question.

utils.get_M is that intended to be a static method?

The code snippet

M = utils.get_M;
function M = get_M
    M = load(fullfile(path, 'M.mat'));
end

cannot be part of a classdef file. It looks rather as being part of a script.

[Deepa Maheshvare]

Sorry for being unclear.

Yes, utils.get_M is a static method

classdef io_utils
    methods(Static)
        function M = get_M
            M = load(fullfile(path, 'M.mat'));
        end
    end
end

[per isakson]

Your class, io_utils, will load M.mat for every call and will thus not improve the performance compared to fun2(t,x), rather the opposite. The class

classdef io_utils
    properties ( Constant )
        M = load('M.mat');
    end
end

loads M.mat once. It's called

>> S = io_utils.M
S = 
  struct with fields:
    A: [7×1001 double]
>> 

[Deepa Maheshvare]

Thanks . So I've

classdef utils
   properties (Constant)
       M = load(fullfile(path, 'M.mat'));
   end
   
    methods(Static)
        function M = get_M
            M = load(fullfile(path, 'M.mat'));
        end
    end
end

And I tried the following ways

Method 1:

function fun1()
            [t,x] = ode15s(@(t,s) fun2(t,x), tspan , x0 ,options);
            % other functions
end

function dx = fun2(t,x)
persistent M
if isempty(M)
   M = utils.get_M;    
end    
end
:
:  
dx = M*x   
end

Method 2:

function fun1()
            [t,x] = ode15s(@(t,s) fun2(t,x), tspan , x0 ,options);
           
end

function dx = fun2(t,x)
M =  utils.M 
end
:
:  
dx = M*x   
end

In the first case, M = utils.get_M is called once and in the second method M = utils.M is called as many times fun2 is called by fun1. From what you have explained, is it right to understand `class utils` is loaded only once even if it's called multiple times.

[per isakson]

Read Define Class Properties with Constant Values and notice especially

MATLAB evaluates the expressions when loading the class. Therefore, the values MATLAB assigns to RN are the result of a single call to the rand function and do not change with subsequent references to NamedConst.RN.

Searching and reading the documentation is a large part of mastering Matlab.

Method 1.

I see no point in using the static method, get_H. It save on overhead to call load() directly in fun2.

Method 2.

Yes. (However, it's more convicing to test than listen to me.)

[Deepa Maheshvare]

Cool! I've read and implemented it already. Thanks.