Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Two options:</p> <ol> <li><p>Follow the proposal you have, but instead of using <code>std::random_device r;</code> to generate your seed sequence for MT, use a different PRNG seeded with <code>m</code>. Choose one that doesn't suffer like MT does from needing a warmup when used with small seed data: I suspect an LCG will probably do. For massive overkill, you could even use a PRNG based on a secure hash. This is a lot like "key stretching" in cryptography, if you've heard of that. You could in fact use a standard key stretching algorithm, but you're using it to generate a long seed sequence rather than large key material.</p></li> <li><p>Continue using <code>m</code> to seed your MT, but <code>discard</code> a large constant amount of data before starting the simulation. That is to say, ignore the advice to use a strong seed and instead run the MT long enough for it to reach a decent internal state. I don't know off-hand how much data you need to discard, but I expect the internet does.</p></li> </ol>
    singulars
    1. This table or related slice is empty.
    1. POMersenne twister warm up vs. reproducibility
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USSteve Jessop
    1. USSteve Jessop
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POMersenne twister warm up vs. reproducibility
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COThe problem is that he is using `std::random_device` to seed the Mersenne Twister on _every_ run, which will (essentially) never have reproducible effects. He can indeed use another PNRG that does not need a warmup phase but he still cannot generate a new seed on every run. He must generate the seed once and store it somewhere between runs to achieve reproducibility. It does not need to be a strong seed, obviously.
      singulars
      1. PO
      1. USAndré Neves
    2. CO@AndréNeves: I don't think the questioner wants a new seed on every run. He wants `M` distinct seeds that (a) are the same on every run; but (b) unlike the values `1 ... M` that he's currently using, are not weak seeds for MT. The question states that he is *not* currently using the `random_device` code. He is currently seeding a MT with a small integer, and the `random_device` code is a proposal that he found on a different SO question, that isn't suitable for him.
      singulars
      1. PO
      1. USSteve Jessop
    3. COOk, I thought he was considering using the above snippet. Anyways, I do understand he wants to have `M` sets of seeds and if he wants to use decent seeds he can use the `random_device` without any problem, he simply has to store it for each dataset. One "cheap" way I remember for not using a strong seed and not havng to store it but still be relatively random is to use a hash of the dataset (or some part) as a seed for the MT (or other PNRG). This way he wouldn't need to store it as it would be deterministic for each dataset.
      singulars
      1. PO
      1. USAndré Neves
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload