timeit

Measure time required to run function

Syntax

t = timeit(f)

t = timeit(f,numOutputs)

Description

t = timeit(f) measures the time (in seconds) required to run the function specified by the function handle f. In order to perform a robust measurement, timeit calls the specified function multiple times and returns the median of the measurements. If the function runs fast, timeit might call the function many times.

t = timeit(f,numOutputs) calls f with the desired number of outputs, numOutputs. By default, timeit calls the function f with one output (or no outputs, if the function does not return any outputs).

Examples

Determine Time to Obtain Current Date

Use timeit to time a function call to date. This example uses a handle to a function that accepts no input.

f = @date;
t = timeit(f)

t = 3.4051e-05

Determine Time to Compute Matrix Summation

Time the combination of several mathematical matrix operations: matrix transposition, element-by-element multiplication, and summation of columns.

A = rand(12000,400);
B = rand(400,12000);
f = @() sum(A.'.*B, 1);
timeit(f)

ans = 0.0223

Compare Time to Run svd with Multiple Outputs

Determine how long it takes to run svd with one output argument, s = svd(X).

X = rand(100);
f = @() svd(X);
t1 = timeit(f)

t1 = 0.0014

Compare the results to svd with three output arguments, [U,S,V] = svd(X).

t2 = timeit(f,3)

t2 = 0.0023

Compare Time to Execute Custom Preallocation to Calling zeros

Create a short function to allocate a matrix using nested loops. Preallocating an array using a nested loop is inefficient, but is shown here for illustrative purposes.

function mArr = preAllocFcn(x,y)
for m = 1:x
    for n = 1:y
        mArr(m,n) = 0;
    end
end
end

Compare the time to allocate zeros to a matrix using nested loops and using the zeros function.

x = 1000;
y = 500;
g = @() preAllocFcn(x,y);
h = @() zeros(x,y);
diffRunTime = timeit(g)-timeit(h)

diffRunTime =

    0.1584

Input Arguments

f — function to be measured

function handle

Function to be measured, specified as a function handle. f is either a handle to a function that takes no input, or a handle to an anonymous function with an empty argument list.

numOutputs — Number of desired outputs from f

integer

Number of desired outputs from f, specified as an integer. If the function specified by f has a variable number of outputs, numOutputs specifies which syntax timeit uses to call the function. For example, the svd function returns a single output, s, or three outputs, [U,S,V]. Set numOutputs to 1 to time the s = svd(X) syntax, or set it to 3 to time the [U,S,V] = svd(X) syntax.

Tips

• The following actions result in unexpected output:

  • Using timeit between tic and toc
  • Using timeit to time a function that includes calls to tic and toc
  • Using timeit recursively