How to time each line of a MatLab script?

Question

Suppose we have a loop:

for i = 1:1000
    A
    B
    C
end

... and I wish to find out the CPU usage spread.

A, B, C are MatLab statements not functions, so (IIUC) I can't use the profiler.

Also in reality I have a dozen lines to cover.

The obvious long-winded way would be:

s = zeros(50, 1);
t = cputime;

for ...
    A
    s(1) = s(1) + (cputime-t);  t = cputime;
    B
    s(2) = s(2) + (cputime-t);  t = cputime;
    :

... which isn't too bad, I suppose.

But can it be improved upon?

I thought of doing:

t = zeros(50, 1);
e(t,0); % reset
for i = 1:1000
    A
    e(1);
    B
    e(2);
    C
    e(3);
end

... with:

function e(t, k)
    if k==0
        last_cputime = cputime;
        return
    end
    t(k) = t(k) + (cputime-last_cputime);
    last_cputime = cputime;
end

But it doesn't see t, so I have to pass that.

Also it doesn't remember last_cputime between invocations, so I need to pass that as well.

So e(last_cputime,t,1)

It's rather ugly. I experimented with using an in-line function:

e = @(k) eval( 't(k) = t(k) + (cputime-last_cputime);  cputime = last_cputime;' );

But I couldn't get this working either:

K>> t = zeros(3,1)
t =
     0
     0
     0


K>> eval( 't(1) = 3' )
t =
     3
     0
     0


K>> e = @(k) eval( 't(k) = 3;' )
e =
  function_handle with value:

    @(k)eval('t(k) = 3;')


K>> e(1)
Attempt to add "t" to a static workspace.
 See Variables in Nested and Anonymous Functions.

Error in pi_test>@(k)eval('t(k) = 3;')

I wonder if another option might be:

for i = 1:1000
    e('A');
    e('B');
    e('C');
end

But then how to code up e?

Is there any way to do avoid horrible ugliness-through-duplication?

Thre is a big button in the edditor called "run and time" that will not only time each line, but also give you histogram like plots and percentages, etc. The profiler does time everything, including matlab statements — Ander Biguri
– Ander Biguri, Commented May 11, 2017 at 9:06
Just curious about your statement regarding profiler: Profiler also measures execution time of expressions. Of course, for each run of a line in a loop the execution time is aggregated and you get only the information overall execution time and the number of how often that line was executed. Do you need to compare execution time of different iterations? Or why is the profiler information not sufficient for you? — souty
– souty, Commented May 11, 2017 at 9:13

Gelliant · Accepted Answer · 2017-05-11 09:15:30Z

1

How about a classdef that handles this?

You can save this as mtime.m

classdef mtime < handle
    properties 
        times
    end
    properties (Access = private)
        t
    end

    methods
        function obj = mtime() %initialize
            obj.t=cputime;
            obj.times=[];
        end
        function time(obj)
            obj.times(end+1) = cputime-obj.t;
            obj.t = cputime;
        end
    end
end

You can then intialize with T=mtime(); and time your code by calling time(T); After the code is finished the timings can be found in T.times.

answered May 11, 2017 at 9:15

Gelliant

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