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Should I use "rand % N" or "rand() / (RAND_MAX / N + 1)"?


Should I use "rand % N" or "rand() / (RAND_MAX / N + 1)"?

By : user2953311
Date : November 20 2020, 01:01 AM
Any of those help If N is a power of two, using the remainder technique is usually safe (RAND_MAX is usually a power of two minus 1, so the entire range has a power of two length). More generally, N has to divide the range of rand() in order to avoid the bias.
Otherwise, you run into this problem, regardless of the quality of rand(). In short, the problem is that you're chopping that range into a number of "parts" each of length N, if N does not divide the range then the last part will not be complete. The numbers that got "cut off" from that part are therefore less likely to occur, since they have one fewer "part" they can be generated from.
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Building R package: "Found 'rand', possibly from 'rand' (C)" NOTE when checking package

Building R package: "Found 'rand', possibly from 'rand' (C)" NOTE when checking package


By : Marcus Mattingly
Date : March 29 2020, 07:55 AM
To fix the issue you can do The discussion in the comments already hits the essential point: R (as of late) complains about use of rand() and srand(). [ Note that that is an R issue, not an Rcpp issue. ]
The reasoning is that at some points in the past, rand() was really bad on some systems. So warnings persist. See eg from this page at cppreference.com:
Does "n * (rand() / RAND_MAX)" make a skewed random number distribution?

Does "n * (rand() / RAND_MAX)" make a skewed random number distribution?


By : CRM Dev
Date : March 29 2020, 07:55 AM
this one helps. Yes, it's skewed, unless your RAND_MAX happens to be a multiple of 10.
If you take the numbers from 0 to RAND_MAX, and try to divide them into 10 piles, you really have only three possibilities:
Where is the official documentation for T-SQL's "ORDER BY RAND()" and "ORDER BY NEWID()"?

Where is the official documentation for T-SQL's "ORDER BY RAND()" and "ORDER BY NEWID()"?


By : Peter Manahan
Date : March 29 2020, 07:55 AM
like below fixes the issue If you're trying to determine why these behave differently, the reason is simple: one is evaluated once, and treated as a runtime constant (RAND()), while the other is evaluated for every single row (NEWID()). Observe this simple example:
WP_Query ordering by "rand" and "name"?

WP_Query ordering by "rand" and "name"?


By : Ebrahim Arzani
Date : March 29 2020, 07:55 AM
help you fix your problem As documented:
What does " rand()% 11" and what's the diffrence between this and "rand()% 10+1"?

What does " rand()% 11" and what's the diffrence between this and "rand()% 10+1"?


By : Mahdi Chawki
Date : September 29 2020, 11:00 PM
this will help The difference between % 11 and %10 +1 can be understood if you try a sample:
%11 gives 11 possible answers: 0,1,2,3,4,5,6,7,8,9,10
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