Dear Sandeep, dear Forum, On 1 Apr 2010, at 23:36, Sandeep Murthy wrote:
> Hi. > > I have a question: is it better / quicker to pass a set of arguments to > a GAP function as a list, or as individual objects? > > Sincerely, S. Murthy. It may depend on several factors, maybe you can try to investigate and optimise your particular example, using the approach shown below. In the first example, initially individual arguments seem to work faster: gap> f1:=function(x) return; end; function( x ) ... end gap> f2:=function(a,b,c) return; end; function( a, b, c ) ... end gap> for i in [1..10000000] do f1([1,2,3]);od;time; 2163 gap> for i in [1..10000000] do f1([1,2,3]);od;time; 2172 gap> for i in [1..10000000] do f1([1,2,3]);od;time; 2172 gap> for i in [1..10000000] do f2(1,2,3);od;time; 1506 gap> for i in [1..10000000] do f2(1,2,3);od;time; 1556 gap> for i in [1..10000000] do f2(1,2,3);od;time; 1519 However, observe that the list [1,2,3] is calculated each time 'f1' is called. If we will create this list before the loop, then it becomes slightly faster than 'f2', since, clearly, GAP parser will parse f1(x) faster than f1(1,2,3): gap> x:=[1,2,3]; [ 1, 2, 3 ] gap> for i in [1..10000000] do f1(x);od;time; 1349 gap> for i in [1..10000000] do f1(x);od;time; 1336 gap> for i in [1..10000000] do f1(x);od;time; 1343 In the second example, we increased the length of the list and the number of arguments to 8: gap> f1:=function(x) return; end; function( x ) ... end gap> f2:=function(a,b,c,d,e,f,g,h) return; end; function( a, b, c, d, e, f, g, h ) ... end gap> for i in [1..10000000] do f1([1,2,3,4,5,6,7,8]);od;time; 2737 gap> for i in [1..10000000] do f1([1,2,3,4,5,6,7,8]);od;time; 2737 gap> for i in [1..10000000] do f1([1,2,3,4,5,6,7,8]);od;time; 2757 gap> for i in [1..10000000] do f2(1,2,3,4,5,6,7,8);od;time; 3149 gap> for i in [1..10000000] do f2(1,2,3,4,5,6,7,8);od;time; 3152 gap> for i in [1..10000000] do f2(1,2,3,4,5,6,7,8);od;time; 3142 Now the list approach works faster. Moreover, if the list to pass to 'f1' will be precomputed in advance, then the timing will be comparable with the one demonstrated in the previous example: gap> t:=[1,2,3,4,5,6,7,8]; [ 1, 2, 3, 4, 5, 6, 7, 8 ] gap> for i in [1..10000000] do f1(t);od;time; 1342 gap> for i in [1..10000000] do f1(t);od;time; 1343 gap> for i in [1..10000000] do f1(t);od;time; 1342 For practical applications, I would say that the overhead is so small (10^7 loop iterations in the examples above to see the difference), that you may select either approach that makes your code easier to read, understand and maintain. Passing arguments in a list, you may need to create this list in advance, and then perform indexation in the function body, and the overhead of these operations may be bigger than passing each argument individually. Note that thinking of arguments as a list may be useful if you need to define a function with a variable number of arguments. GAP allows to to this, if a function is defined with exactly one formal argument with the special name 'arg': the values of all the actual arguments are stored in a list assigned to the new variable corresponding to the formal argument 'arg'. There are two typical scenarios for wanting such a possibility: having optional arguments and having any number of arguments. Hope this helps, Alexander _______________________________________________ Forum mailing list Forum@mail.gap-system.org http://mail.gap-system.org/mailman/listinfo/forum
