Menu
I quite like being able to generate the same set of pseudo-random data repeatedly, especially with tweaking experimental code. Through observation I would say that rand() seems to give the same sequence of numbers each time*.
Is it guaranteed to do this for repeated executions on the same machine / for different machines / for different architectures?
*For the same seed obviously.
549
The RAND function in stand-alone applications generates the same numbers each time you run your application because the uniform random number generator that RAND uses is initialized to same state when the application is loaded.
One simple way to avoid repeating the same random numbers in a new MATLAB session is to choose a different seed for the random number generator. rng gives you an easy way to do that, by creating a seed based on the current time. Each time you use 'shuffle' , it reseeds the generator with a different seed.
Description. RAND returns an evenly distributed random real number greater than or equal to 0 and less than 1. A new random real number is returned every time the worksheet is calculated. Note: As of Excel 2010, Excel uses the Mersenne Twister algorithm (MT19937) to generate random numbers.
Every time you call rand() it takes the seed and/or the last random number(s) generated (the C standard doesn't specify the algorithm used, though C++11 has facilities for specifying some popular algorithms), runs a mathematical operation on those numbers, and returns the result.
Yes, given the same environment for the program. From the C standard §7.20.2.2/2,
The
srandfunction uses the argument as a seed for a new sequence of pseudo-random numbers to be returned by subsequent calls torand. Ifsrandis then called with the same seed value, the sequence of pseudo-random numbers shall be repeated. Ifrandis called before any calls tosrandhave been made, the same sequence shall be generated as whensrandis first called with a seed value of 1.
Of course, this assumes it is using the same implementation detail (i.e. same machine, same library at the same execution period). The C standard does not mandate a standard random number generating algorithm, thus, if you run the program with a different C standard library, one may get a different random number sequence.
See the question Consistent pseudo-random numbers across platforms if you need a portable and guaranteed random number sequence with a given seed.
123
It is guaranteed to give the same sequence for the same seed passed to srand() - but only for the duration of a single execution of the program. In general, if an implementation has a choice in behaviour, there is no specific requirement for that choice to remain the same across subsequent executions.
It would be conforming for an implementation to pick a "master seed" at each program startup, and use that to perturb the pseudo-random number generator in a way that is different each time the program starts.
If you wish for more determinism, you should implement a PRNG with specific parameters in your program.
34
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
