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10 Nov 2008	fastsearch Search an element in the array, or the next smaller and greater Author: Valentin Kuklin	Franworth, Dru	I tried the following code in Matlab clear all x=randn(10000,1); tic for i=1:1000000 y=randn; g=find(abs(x-y)==min(abs(x-y))); end toc tic y=sort(x); for i=1:1000000 z=randn; qq=fastsearch(y,z,1); end toc ---------------------------------------------------------------------------------- This is the output: Elapsed time is 423.486252 seconds. Elapsed time is 357.878006 seconds. ----------------------------------------------------------------------------------- An improvement by 15%. Pretty impressive.
10 Nov 2008	fastsearch Search an element in the array, or the next smaller and greater Author: Valentin Kuklin	Franworth, Dru	There is a slight bug in your code. In line 134 , you should have index=fastsearch_indeed(array,von,m1-1,wert,bias); Instead, you have fastsearch(array,von,m1-1,wert,bias); Same thing for line 136. Basically, all you have to do is replace fastsearch in lines 134 and 136 with fastsearch_indeed.
09 Nov 2008	fastsearch Search an element in the array, or the next smaller and greater Author: Valentin Kuklin	Franworth, Dru	I tried the following code and got an error message. As you can see, the number I am searching for is inside the sorted vector but it is generating an error message. ----------------------------------------------------------------------------------- >> x=randn(10000,1); >> y=sort(x); >> z=randn; >> fastsearch(y,z,1) ??? Error using ==> fastsearch Too many input arguments. Error in ==> fastsearch>fastsearch_indeed at 137 index=fastsearch(array,m2+1,bis,wert,bias); Error in ==> fastsearch at 59 index = fastsearch_indeed(array,1,length(array),wert,bias); >> z z = 0.4291 >> min(y) ans = -3.5758 >> max(y) ans = 4.0050 >> find(abs(y-z)==min(abs(y-z))) ans = 6694
06 May 2008	fastsearch Search an element in the array, or the next smaller and greater Author: Valentin Kuklin	Kuklin, Valentin	Hi Alexander, thanks for your notes. I think there is no bug. This code with "Check if wert is inside of array." is used only for the first run, for example if you have array=1:1:100 and you search -5 or 105. For the further runs it does not play any role, the searched number will be anyway within [von, bis]. Actually it can not be infinite recursion because every "if" ends with "return" but not with the new call of function. But anyway I am happy that someone uses my function and tries to find bugs :) Thanks again :) Valentin Kuklin
05 May 2008	fastsearch Search an element in the array, or the next smaller and greater Author: Valentin Kuklin	Chemeris, Alexander	It's good that such a useful algorithm in finally implemented in Matlab :) But this implementation have a bug. "Check if wert is inside of array." should looks like: if wert<array(von) if bias==1 index=von; return; else index=-1; return; end end if wert>array(bis) if bias == -1 index = bis; return; else index = -1; return; end end That is "von" and "bis" are used instead of "1" and "end". Without this fix algorthm may enter infinite recursion in certain cases.
19 Oct 2007	fastsearch Search an element in the array, or the next smaller and greater Author: Valentin Kuklin	(us) schwarz, urs	sorry, this was not copy/pasted properly at the end of the code example: -or- if you feel that ISSORTED eats too much time, simplify it to function ix=fastsearch(a,v,b) ix=fas(a,1,numel(a),v,b); end which comes with no additional cost... us
19 Oct 2007	fastsearch Search an element in the array, or the next smaller and greater Author: Valentin Kuklin	(us) schwarz, urs	a very nice utility; a user-friendly improvement could look like this 1) make <fastsearch> a subroutine, eg, <fas> 2) add a main routine, which takes care of some preprocessing, which - otherwise - may be missed by the user 3) add a bit more help... % eg, function ix=fastsearch(a,v,b) if ~issorted(a) a=sort(a); end ix=fas(a,1,numel(a),v,b); end % your function <fastsearch> renamed to <fas> % ... % just a thought us
18 Oct 2007	fastsearch Search an element in the array, or the next smaller and greater Author: Valentin Kuklin	Cao, Yi	Excellent. Compare with tic,c=find(b==b(123456));toc Elapsed time is 0.168458 seconds. >>c c = 123456 --------------------------------- tic,[dum,c]=min(abs(b-0.16234));toc Elapsed time is 0.487312 seconds. >>0.16234-b(c) ans = -6.9258e-008 >>0.16234-b(c-1) ans = 2.3127e-007 It is more than 100 times faster than these normal ways to get similar answers in matlab. The weak point is that the array has to be sorted first. It will take more than 2 seconds to sort a array of size about 10^7. However, it could be useful for cases where repeated searches are required. One more thing, I guess using the golden ratio might be even more efficient.
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