0 个投票

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.

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 采纳的回答

per isakson
per isakson 2020-5-5

0 个投票

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

7 个评论
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Deepa Maheshvare
Deepa Maheshvare 2020-5-5
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
per isakson 2020-5-5
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
Deepa Maheshvare 2020-5-5
编辑：per isakson 2020-5-5
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
per isakson 2020-5-5
编辑：per isakson 2020-5-5
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
Deepa Maheshvare 2020-5-5
编辑：Deepa Maheshvare 2020-5-5
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
per isakson 2020-5-5
编辑：per isakson 2020-5-5
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
Deepa Maheshvare 2020-5-6
编辑：per isakson 2020-5-7
Cool! I've read and implemented it already. Thanks.

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