find the minimal value of a vector
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I wanna find the minimal value of column b with logical c of vector a. When b is super big , max operation takes a very long time(as shown in fig below). How to vectorize the for loop to reduce the calling times of max (the simplified code is shown below)?
a=[1 3 4 52];
b=[2 3 4];%column index
c=logical([1 0 1;1 1 0; 0 0 1]);
Walter Roberson 2018 年 4 月 30 日
No, there is no faster version. We discussed this already in one of your previous questions where you were asking about max(). As I said then in https://www.mathworks.com/matlabcentral/answers/397675-is-there-a-faster-version-of-min#comment_561596
"If you break out the timing, you will likely find that the cost is in extracting the sub-array c(1,d) to send to the min() function. min() is at worst a linear operation (I say at worst because in theory it could be run in parallel for sufficiently large arrays.)"
If you calculate
You can see that it is taking about 6.6E-7 seconds per iteration. That is twice as fast as just making one anonymous function call:
>> timeit(@() fun(),0)
so that is really pretty efficient; the Just In Time compiler must be doing a really good job with it.