📄 random.mldoc
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<!-- random.mldoc --><!DOCTYPE ML-DOC SYSTEM><COPYRIGHT OWNER="Bell Labs, Lucent Technologies" YEAR=1998><VERSION VERID="1.1" YEAR=1998 MONTH=5 DAY=6><TITLE>The Random structure</TITLE><INTERFACE><HEAD>The <CD/Random/ structure</HEAD><SEEALSO> <STRREF TOPID/Rand/</SEEALSO><PP>The <STRREF NOLINK/Random/ structure implements a random number generator using a subtract-with-borrow(SWB) generator as described in Marsaglia and Zaman, "A New Class of Random Number Generators," <IT/Ann. Applied Prob./ 1(3), 1991, pp. 462-480.<PP>The SWB generator is a 31-bit generator with lags 48 and 8. It has period<MATH>(2<SUP/1487/ - 2<SUP/247/)/105</MATH> or about <MATH/10<SUP/445//. Although generally excellent,they act locally like a lagged Fibonacci generatorand thus have troubles with the birthday test. To repair this, theimplementation provided here incorporates a suggestion of Marsaglia and Zaman,and combines the SWB generator with alinear congruential generator, specifically <MATH/(48271*a)mod(2<SUP/31/-1)/.<STRUCTURE STRID="Random"> <OPAQUE> <SIGBODY SIGID="RANDOM" FILE=RANDOM> <SPEC> <TYPE><ID>rand <COMMENT> <PP> encapsulates state for the random number generator. <SPEC> <VAL>rand<TY>(int * int) -> rand <COMMENT> <PROTOTY> rand (<ARG/i/, <ARG/j/) </PROTOTY> creates the initial seed for the random number generator based on the integers <ARG/i/ and <ARG/j/. <SPEC> <VAL>toString<TY>rand -> string <VAL>fromString<TY>string -> rand <COMMENT> <PP> These functions convert between generator state and a string representation of that state. The string representation is not necessarily printable. <CD/fromString/ is only guaranteed to work on the output of <CD/toString/, in which case <CD/fromString o toString/ is the identity function. A string in an incorrect format will cause <CD/fromString/ to raise the exception. <PP> These functions allow the state of a generator to be saved, in order that the generator can be replicated at a later time. <SPEC> <VAL>randInt<TY>rand -> int <COMMENT> <PROTOTY> randInt <ARG/s/ </PROTOTY> generates random integers uniformly in the range <MATH/[<CD/Int.minInt/,<CD/Int.maxInt/]/ based on the information in <ARG/s/. As a side-effect, the function updates the internal state of <ARG/s/. <SPEC> <VAL>randNat<TY>rand -> int <COMMENT> <PROTOTY> randNat <ARG/s/ </PROTOTY> generates random integers uniformly in the range <MATH/[<CD/0/,<CD/Int.maxInt/]/ based on the information in <ARG/s/. As a side-effect, the function updates the internal state of <ARG/s/. <SPEC> <VAL>randReal<TY>rand -> real <COMMENT> <PROTOTY> randReal <ARG/s/ </PROTOTY> generates random integers uniformly in the range <MATH/(0.0,1.0)/ based on the information in <ARG/s/. As a side-effect, the function updates the internal state of <ARG/s/. <SPEC> <VAL>randRange<TY>(int * int) -> rand -> int <RAISES><EXNREF DOCUMENT=SML-BASIS-DOC STRID="General"/Fail/ <COMMENT> <PROTOTY> randRange (<ARG/i/, <ARG/j/) <ARG/s/ </PROTOTY> generates random integers uniformly in the range <MATH/[<ARG/i/, <ARG/j/]/ based on the information in <ARG/s/. As a side-effect, the function updates the internal state of <ARG/s/. This raises the exception <EXNREF DOCUMENT=SML-BASIS-DOC STRID="General"/Fail/ if <MATH/<ARG/j/ < <ARG/i//.</STRUCTURE></INTERFACE>⌨️ 快捷键说明
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