This experiment on R2013a 64bit, Win7 and 8GB suggests
- try make K global
- a copy of val is created by cssm_passing_by_value(val) (and Task Manager confirms)
- however, it does not explain your 25s(?)
>> global val
>> val = randn( 1e4 );
>> cssm_global() ;
Elapsed time is 0.000007 seconds. <<<<<<<<<<<<<<<<<
Elapsed time is 0.000001 seconds.
>> val = cssm_passing_by_value( val ) ;
Elapsed time is 0.506452 seconds. <<<<<<<<<<<<<<<<<<
Elapsed time is 0.000003 seconds.
>>
where
function cssm_global()
global val
tic, val( 111,113 ) = val( 1111, 1133 ); toc
tic, val( 119,119 ) = val( 5111, 5133 ); toc
end
and where
function val = cssm_passing_by_value( val )
tic, val( 111,113 ) = val( 1111, 1133 ); toc
tic, val( 119,119 ) = val( 5111, 5133 ); toc
end
.
Surprising result with passing "by value"
I've made another few confusing experiments. (I don't think confusing, because of mistakes on my part, but [...].) Here is one such result:
- the long execution time disappears when I successively pass the array to sub-functions and change an element at each level - unbelievable
>> val = randn( 1e4 );
>> val = cssm_passing( val );
Elapsed time is 0.000004 seconds. <<<<<<<<<<<<<<<<
Elapsed time is 0.000001 seconds.
where ( I've renamed the old m-file se above.)
function val = cssm_passing ( val )
val(1,1) = 1;
val = sub_passing( val );
end
function val = sub_passing( val )
val(2,2) = 2;
val = sub2_passing( val );
end
function val = sub2_passing( val )
tic, val( 111,113 ) = val( 1111, 1133 ); toc
tic, val( 119,119 ) = val( 5111, 5133 ); toc
end
I've tested with these three functions in one m-file and in three, respectively. The result was the same in both cases.
