# Changes between Version 3 and Version 4 of IntroGrid

Ignore:
Timestamp:
05/02/12 09:32:32 (8 years ago)
Comment:

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Unmodified
 v3 Suppose you want to generate 1 million events. With the gridpack you could choose to do 200 runs in which each run generates N=5000 events. (Remember to use a different random number seed for each run). Each of the event samples returned by a single gridpack run has a physically distributed set of events, i.e. with an expected error of sqrt(5000)=71. So the granularity can safely be set to the same number as giving it a lower value does not improve the error. Because the error is relatively large, there might be many important subprocesses that are not evaluated, but because the channels are chosen randomly, each gridpack run evaluates a different set of channels such that the total error on the 1 million events is only sqrt(10^6)=1000. In specific cases the granularity could be increased, ''e.g.'', if you know beforehand that you will produce a lot of events. In this example, where the total number of events will be a million, the uncertainty will be sqrt(10^6){{{ 1000. Hence the granularity could have been set to 1000 as this will generate at least 1000 events for each channel. Hence you'll never be off by more than 1000 events. (The value for the granularity can be set by passing it as the 3rd argument when executing the }}}./run.sh= script). However, this should be used with great care, because in the case where not all the gridpack jobs can be retrieved, or if only a subset of the total number of events is analyzed, you are making an error. It is therefore '''highly recommended to not touch the default value for the granularity''' at leave the 3rd argument of the =./run.sh= script empty. In specific cases the granularity could be increased, ''e.g.'', if you know beforehand that you will produce a lot of events. In this example, where the total number of events will be a million, the uncertainty will be $\sqrt{10^6}=1000$. Hence the granularity could have been set to 1000 as this will generate at least 1000 events for each channel. Hence you'll never be off by more than 1000 events. (The value for the granularity can be set by passing it as the 3rd argument when executing the {{{./run.sh}}} script). However, this should be used with great care, because in the case where not all the gridpack jobs can be retrieved, or if only a subset of the total number of events is analyzed, you are making an error. It is therefore '''highly recommended to not touch the default value for the granularity''' at leave the 3rd argument of the =./run.sh= script empty.