InputParser vs exist(...,'var') vs nargin performance - performance

Question

Is there any performance comparison among those three variants for input checking/default initializaion?
It would be useful a comparison on a recent version e.g. R2014b and and older one R2012b.
An example:
function foo(a,b)
if nargin < 1, a = 1; end
if nargin < 2, b = 2; end
end
versus
function foo(a,b)
if exist('a','var'), a = 1; end
if exist('b','var'), b = 2; end
end
versus
function foo(varargin)
p = inputParser;
addOptional(p,'a',1)
addOptional(p,'b',2)
parse(p,varargin{:})
end
Using Amro's testing suite, on R2014b:
func nargs time
_________________ _____ __________
'foo_nargin' 0 2.3674e-05
'foo_exist' 0 3.1339e-05
'foo_inputparser' 0 9.6934e-05
'foo_nargin' 1 2.4437e-05
'foo_exist' 1 3.2157e-05
'foo_inputparser' 1 0.0001307
'foo_nargin' 2 2.3838e-05
'foo_exist' 2 3.0492e-05
'foo_inputparser' 2 0.00015775

Answer 1

Here is some code to test the three approaches:
function t = testArgParsing()
args = {1, 2};
fcns = {
#foo_nargin ;
#foo_exist ;
#foo_inputparser
};
% parameters sweep
[f,k] = ndgrid(1:numel(fcns), 0:numel(args));
f = f(:); k = k(:);
% test combinations of functions and number of input args
t = cell(numel(f), 3);
for i=1:size(t,1)
t{i,1} = func2str(fcns{f(i)});
t{i,2} = k(i);
t{i,3} = timeit(#() feval(fcns{f(i)}, args{1:k(i)}), 2);
end
% format results in table
t = cell2table(t, 'VariableNames',{'func','nargs','time'});
end
function [aa,bb] = foo_nargin(a,b)
if nargin < 1, a = 1; end
if nargin < 2, b = 2; end
aa = a;
bb = b;
end
function [aa,bb] = foo_exist(a,b)
if ~exist('a','var'), a = 1; end
if ~exist('b','var'), b = 2; end
aa = a;
bb = b;
end
function [aa,bb] = foo_inputparser(varargin)
p = inputParser;
addOptional(p,'a',1);
addOptional(p,'b',2);
parse(p, varargin{:});
aa = p.Results.a;
bb = p.Results.b;
end
Here is what I get in R2014a on my machine:
>> t = testArgParsing
t =
func nargs time
_________________ _____ __________
'foo_nargin' 0 3.4556e-05
'foo_exist' 0 5.2901e-05
'foo_inputparser' 0 0.00010254
'foo_nargin' 1 2.5531e-05
'foo_exist' 1 3.7105e-05
'foo_inputparser' 1 0.0001263
'foo_nargin' 2 2.4991e-05
'foo_exist' 2 3.6772e-05
'foo_inputparser' 2 0.00015148
And a pretty plot to view the results:
tt = unstack(t, 'time', 'func');
names = tt.Properties.VariableNames(2:end);
bar(tt{:,2:end}.')
set(gca, 'XTick',1:numel(names), 'XTickLabel',names, 'YGrid','on')
legend(num2str(tt{:,1}, 'nargin=%d'))
ylabel('Time [sec]'), xlabel('Functions')