## File: modrandom.f90

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elkcode 5.4.24-2
 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748  ! Copyright (C) 2012 J. K. Dewhurst, S. Sharma and E. K. U. Gross. ! This file is distributed under the terms of the GNU General Public License. ! See the file COPYING for license details. module modrandom ! random number generator state integer(8) rndstate(0:5) data rndstate / 799047353, 1322018920, 1014372120, 1198189977, 832907020, & 5678910 / contains !BOP ! !ROUTINE: randomu ! !INTERFACE: real(8) function randomu() ! !DESCRIPTION: ! Generates random numbers with a uniform distribution in the interval $[0,1]$ ! using the fifth-order multiple recursive generator of P. L'Ecuyer, ! F. Blouin, and R. Coutre, {\it ACM Trans. Modeling Comput. Simulation} ! {\bf 3}, 87 (1993). The sequence of numbers $r_i$ is produced from ! $$x_i=(a_1 x_{i-1}+a_5 x_{i-5})\mod m$$ ! with $r_i=x_i/m$. The period is about $2^{155}$. ! ! !REVISION HISTORY: ! Created January 2012 (JKD) ! Changed initial state, April 2017 (JKD) !EOP !BOC implicit none ! local variables ! parameters taken from the GNU Scientific Library (GSL) integer(8), parameter :: a1=107374182, a5=104480, m=2147483647 integer(8) i,i1,i5 data i / 0 / i=modulo(i+1,6_8) i1=modulo(i-1,6_8) i5=modulo(i-5,6_8) rndstate(i)=int(mod(a1*rndstate(i1)+a5*rndstate(i5),m)) randomu=dble(rndstate(i))/dble(m) end function !EOC end module