12.07.2015 Views

PGI Fortran - Servidor WWW del Cluster Ladon-Hidra

PGI Fortran - Servidor WWW del Cluster Ladon-Hidra

PGI Fortran - Servidor WWW del Cluster Ladon-Hidra

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destis an integer variable or array element that represents the destinationlocation.a5 is an integer expression that identifies the starting position within a4,for the bits being transferred.RANThe RAN subroutine returns the next number from a sequence of pseudo-random numbers ofuniform distribution over the range 0 to 1. The result is a floating point number that is uniformlydistributed in the range between 0.0 and 1.0 exclusive. It has the form:y = RAN(i)where y is set equal to the value associated by the function with the seed argument i. The argumenti must be an INTEGER*4 variable or INTEGER*4 array element.The argument i should initially be set to a large, odd integer value. The RAN function stores avalue in the argument that it later uses to calculate the next random number.There are no restrictions on the seed, although it should be initialized with different values onseparate runs in order to obtain different random numbers. The seed is updated automatically, andRAN uses the following algorithm to update the seed passed as the parameter:SEED = 6969 * SEED + 1 ! MOD 2**32The value of SEED is a 32-bit number whose high-order 24 bits are converted to floating point andreturned as the result.If the command-line option to treat all REAL declarations as DOUBLE PRECISION declarationsis in effect, RAN returns a DOUBLE PRECISION value.SECNDSThe SECNDS subroutine provides system time of day, or elapsed time, as a floating point value inseconds. It has the form:y = SECNDS(x)where (REAL or DOUBLE PRECISION) y is set equal to the time in seconds since midnight,minus the user supplied value of the (REAL or DOUBLE PRECISION) x. Elapsed timecomputations can be performed with the following sequence of calls.284 Chapter 7

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