email1<-function(n,lambda,n.days){
  #vertex set (n people)
  V=1:n
  #starting time of simulation
  tm<-0
  #initialize 
  tms<-NULL
  sender<-NULL
  receiver<-NULL
  while (tm<n.days){
    tm<-tm+rexp(1,n*(n-1)*lambda)
    snd<-sample(V,1)
    rcv<-sample(setdiff(V,snd),1)
    #save relational event
    tms<-c(tms,tm)
    sender<-c(sender,snd)
    receiver<-c(receiver,rcv)
  }
  remdat<-data.frame(tms=tms,sender=sender,receiver=receiver)
  return(remdat)
}

remdat1<-email1(n=10,lambda=0.1,n.days = 14)
remdat1



email2<-function(n,lambda.WD,lambda.WE,n.days){
  #vertex set (n people)
  V=1:n
  #starting time of simulation (a Monday)
  tm<-0
  #initialize 
  tms<-NULL
  sender<-NULL
  receiver<-NULL
  while (tm<n.days){
    # decide which lambda to use
    day<-tm%%7
    if (day<5){
      lambda<-lambda.WD
      WD<-TRUE
    } else {
      lambda<-lambda.WE
      WD<-FALSE
    }
    
    delta.tm<-rexp(1,n*(n-1)*lambda)
    
    if ((WD & (day+delta.tm<5))|(!WD & (day+delta.tm<7))){
      tm<-tm+delta.tm
      snd<-sample(V,1)
      rcv<-sample(setdiff(V,snd),1)
      #save relational event
      tms<-c(tms,tm)
      sender<-c(sender,snd)
      receiver<-c(receiver,rcv)
    } else {
      if (WD){
        tm<-(tm%/%7)*7+5
      } else {
        tm<-(tm%/%7)*7+7
      }
    }
  }
  remdat<-data.frame(tms=tms,sender=sender,receiver=receiver)
  return(remdat)
}

remdat2<-email2(n=10,lambda.WD=0.1,lambda.WE=0.01,n.days = 14)
remdat2




email3<-function(n,lambda.WD,lambda.WE,b1,b2,n.days){
  #vertex set (n people)
  V=1:n
  #starting time of simulation (a Monday)
  tm<-0
  #initialize 
  tms<-NULL
  sender<-NULL
  receiver<-NULL
  rep<-matrix(-Inf,ncol=n,nrow=n)
  rec<-matrix(-Inf,ncol=n,nrow=n)
  while (tm<n.days){
    # decide which lambda to use
    day<-tm%%7
    if (day<5){
      lambda0<-lambda.WD
      WD<-TRUE
    } else {
      lambda0<-lambda.WE
      WD<-FALSE
    }
    
    lambda<-lambda0*exp(b1*(tm-rec<2)+b2*(tm-rep<2))
    diag(lambda)<-0
    
    delta.tm<-rexp(1,sum(lambda))
    
    if ((WD & (day+delta.tm<5))|(!WD & (day+delta.tm<7))){
      tm<-tm+delta.tm
      event<-sample(1:n^2,1,prob=lambda/sum(lambda))
      snd<-(event-1)%%n+1
      rcv<-(event-1)%/%n+1
      #save relational event
      tms<-c(tms,tm)
      sender<-c(sender,snd)
      receiver<-c(receiver,rcv)
      #update reciprocity and repetition
      rep[snd,rcv]<-tm
      rec[rcv,snd]<-tm
    } else {
      if (WD){
        tm<-(tm%/%7)*7+5
      } else {
        tm<-(tm%/%7)*7+7
      }
    }
  }
  remdat<-data.frame(tms=tms,sender=sender,receiver=receiver)
  return(remdat)
}

remdat3<-email3(n=10,lambda.WD=0.1,lambda.WE=0.01,b1=0,b2=2,n.days = 14)
remdat3