#<
# Noise
#
# Usage
#   Noise <in >out gauss=0 mean=0. var=0.333 seed=123456 rep=0
#
# INPUT PARAMETERS
# gauss   -  integer   [0] produces a gaussian distribution if non-zero
#                      and a uniform distribution if zero
# mean    -  integer   [0] mean of the random number distribution
# var     -  real      variance of distribution defaults to 1/3 for uniform 
#                      distribution this creates numbers between -1 and +1 
#                      for mean=0 variance of distribution defaults to 1 
#                      for a gaussian distribution.	
# seed    -  integer   integer to start random number generator
#                      default=number of seconds from the first of the year
# rep     -  integer   replace samples of trace by random noise
#                      default=0 (add random noise)
#                      if !=0 the traces are replaced with random noise   
#
# DESCRIPTION
# Add random noise
#
# COMMENTS
#  The default operation of this routine is to add random numbers uniformly
#  distributed between -1.0 and +1.0 using a seed taken from the time.
#
#  Samples:  For uniformly distributed numbers between -0.2 and 0.2, use 
#            var=0.0667, or 0.2 * 1/3.
#     
#            For uniformly distributed numbers between 0 and 1, use mean=0.5
#            and var=0.1667, or 0.5 * 1/3.
#
# CATEGORY
# Seis:Filter
#
# COMPILE LEVEL
# DISTR
#>
#%
# Author - Ray Abma
#
# ----------
#  Keyword: add gaussian noise random variance 
# ----------
#
#
integer n1,n2,n3,esize
integer gauss,seed,rep,seedin
real mean,var,varin
integer ftime

# fetch dimensions & esize  
from either:	integer n1,n2,n3=1,esize=4

# fetch parameters 
from par:       integer gauss=0
from par:       real mean=0.
from par:       real var=0.
from par:       integer rep=0

 if( getch('var','f',varin) > 0) {
     var = varin
     }
 else {
     if ( gauss == 0) {
        var = 1.0/3.0
        }
     else {
        var = 1.0
     }
 }

 if( getch('seed','i',seedin) > 0) {
     seed = seedin
     }
 else {
     seed = 1997
     }
#
 if (seed <= 0) seed = 1
 call putch('seed','i',seed)

call  hclose();

allocate:	real databuf(n1)

subroutine Noise( n1,n2,n3,esize,databuf,
            gauss,mean,var,seed,rep)
integer n1,n2,n3,itr,i,esize
integer gauss,seed,rep
real mean,var
real rnd
real databuf(n1)

      call rseed(seed)

do itr=1,n2*n3{					# loop over traces

    call sreed( 'in', databuf, n1*esize )		# read trace

    if ( rep != 0 ) { do i=1,n1 { databuf(i) =0. } } # zero trace

	   do i=1,n1 {
	     if (gauss .eq. 0) {
  	         call randm(rnd)
                 rnd = (2 * rnd - 1.0) * 3.0
	     }
	     else {
	         call grand(rnd)
             }
             rnd = var * rnd + mean
	     databuf(i) = databuf(i) + rnd
	   }

    call srite('out', databuf, n1*esize)		#write trace

}

return; end