| command (MEL) |
Only available in
MEL |
rand
|
In categories: Language, Math |
Go to: Synopsis. Return value. Related.
MEL examples.
rand [string|int] float|vector
[float|vector]
rand is NOT undoable, NOT queryable, and NOT
editable.
The command returns random numbers evenly distributed over the
range 0->range or in the case of the second version between
start_range and end_range. The vector version generates an
independent random number for each of the three components.
Multiple random number streams:
The three stream-based variants of rand accept a stream name
parameter which specifies the name of the random number stream to
use when generating random numbers. For details on random number
streams please refer to the section "An overview of MEL's multiple
random number stream support" later in this document. The behaviour
of the function is identical to the non-stream versions with the
exception that random number generation is performed from the
specified rather than the default random number stream. The first
two stream-based variants take a string which specifies the stream
name. The third variant takes an integer as the stream name (this
is a convenience function which internally converts the integer to
a string in the event the use wants to work with numeric-only
stream names). An overview of MEL's multiple random number
stream support:
The random numbers returned by rand, sphrand and
gauss all follow a fixed sequence (called a random number
stream). Prior to the addition of multiple random number
streams to Maya, the only way to ensure repeatability was to
explicitely reseed the generator using the seed function.
There are, however, cases where random calls occur in arbitrary
order and reseeding is either impossible or impractical. To resolve
this issue, MEL supports an arbitrary number of user-defined random
number streams. Each MEL random call (rand, sphrand,
gauss, etc) allows a stream name to be provided which
identifies the random stream to be used during random number
generation. Streams are created implicitely: each MEL random
function checks first if the stream exists and if not, it is
created and seeded with an internal default. The internal default
is identical so that the default and user-defined streams always
generate the same sequence of numbers when generated via an
identical set of random calls. (This repeatability can be avoided
by manually reseeding the stream via the seed function).
Stream names may be any user-defined string not containing a "*" as
a character. The stream named "default" is pre-defined and refers
to the standard stream used by the non-stream-based MEL random
calls. The intent with random number streams is that the user can
target specific areas of MEL random calls to use dedicated random
number streams and thus ensure repeatability of the random numbers
which are generated. Internally, streams are managed through an
efficient database, so it is not unreasonable to allocate large
stream counts (e.g. 100,000 streams). Streams may be deleted via
the delrandstr function. The state of a random number stream
may be queried via the randstate function.
delrandstr, gauss, seed, sphrand
rand 42;
// Result: 39.1327 //
rand 42;
// Result: 23.8585 //
rand -80 42;
// Result: -12.1565 //
rand <<1,1,1>>;
// Result: <<0.531557, 0.920261, 0.515431>> //
rand <<1,1,1>> <<100, 200, 300>>;
// Result: <<81.2325, 38.4956, 266.008>> //
// <b>Multiple random number stream examples:</b><br>
string $s1 = "stream1";
// Result: stream1 //
rand $s1 42;
// Result: 39.1327 //
rand $s1 42;
// Result: 23.8585 //
string $s2 = "stream2";
// Result: s2 //
rand $s2 42;
// Result: 39.1327 //
rand $s2 42;
// Result: 23.8585 //
// Example using the convenience method which allows an integer to be used
// as the stream name:
// Assume `particleID' is an integer... //
rand particleID -80 42;
// Result: 33.6711 //