MATLAB: Wait to execute commands

command windowtictimetoc

Hi, I am trying to write the following matlab code:

tic
for a=A
if (a==8)
disp('I found it');
break;
end
end
toc

but the moment I write tic in the command window it starts counting time, how can I tell matlab to start counting time only when the whole code in written?

Best Answer

tic will restart the counter whenever you run it. So you don't need to worry if you ran tic several times before. Just run it after you have finished your code, and it will count from that point forward.

Related Solutions

MATLAB: Estimate time needed for a code to finish

This is my favourite solution:

   tic
   for i = 1:1e9
      if toc > 10
         fprintf('Iteration %d/%d\n',i,1e9)
         tic
      end
      % Very hard calculation
   end

MATLAB: Avarage running time problem

Here are three ways to use tic/toc to measure the timing of a loop. Each method has pros and cons.

Method 1: Least overhead & resolution

The tic() & toc() functions require processing time, albeit a very small amount. Storing the results of toc() also requires processing time. This method contains the least overhead but you don't get the single-iteration times.

start = tic(); 
for i=1:100
    1+1;
    2+2;
end
k= toc(start)/100;

Method 2: Single iterations times

This method gives you the single-iteration times but the processing time is added by tic/toc and storing the toc output.

t = nan(1, 100); 
for i=1:100
    start = tic(); 
    1+1;
    2+2;
    t(i)=toc(start);
end
k=mean(t)

Method 3: Single iterations times, less overhead

This method removes tic() from the loop which doesn't reduce the overhead by much but it's worth sharing. The single-iteration times are computed outside of the loop.

t = nan(1, 101); 
start = tic(); 
t(1) = toc(start); 
for i=1:100
    1+1;
    2+2;
    t(i+1)=toc(start);
end
k=mean(diff(t))
% Compare that to (t(end)-t(1))/100

Reasons your timing was off

tic() returns an integer (uint64) that has meaning only for the toc function. Example: t = tic(); t = 1943576784277
toc() returns the elapsed time since the previous tic() which is very quick in your loop so you're subracting a tiny amount from a large, meaningless integer.
The 1+1 and 2+2 lines display the result of each iteration in the command window since those lines are not supressed with a semicolon (;). That takes a lot of time.
The t variable was not pre-allocated so the length of t grows with each iteration. That also takes a lot of time.

Since the computations are so simple, you'll find a wide range of mean(t) if you run that script many times. Consider using the timeit function.

Best Answer

Related Solutions

MATLAB: Estimate time needed for a code to finish

MATLAB: Avarage running time problem

Related Question