R/prime.implicants.R

In mcbiopi: Matrix Computation Based Identification of Prime Implicants

prime.implicants<-function(mat){
	if(is.vector(mat) || nrow(mat)==1)
		stop("'mat' must have at least 2 rows.")
	mat[mat==0]<- -1
	n.var<-ncol(mat)
	if(is.null(colnames(mat)))
		colnames(mat)<-paste("X",1:n.var,sep="")
	ia<-ia.samp(n.var)
	ia.rowS<-rowSums(ia)
	vec.primes<-character(0)
	list.cover<-list()
	mat.in<-NULL
	name.paste<-function(x){
		x<-x[x!=""]
		paste(x,collapse=" & ")
	}
	for(i in 1:n.var){
		pairt<-ia.samp(i,conj=-1)
		n.p<-nrow(pairt)
		ia2<-matrix(ia[ia.rowS==i,],ncol=n.var)
		tmp<-matrix(0,nrow(ia2)*n.p,n.var)
		for(j in 1:nrow(ia2))
			tmp[((j-1)*n.p+1):(j*n.p),ia2[j,]==1]<-pairt
		if(length(vec.primes)>0){
			tmp9<-tmp%*%t(mat.in)
			tmp10<-diag(mat.in%*%t(mat.in))
			tmp11<-t(tmp10)%x%rep(1,nrow(tmp))==tmp9
			tmp.in<-which(rowSums(tmp11)==0)
			tmp<-tmp[tmp.in,]
		}
		tmp2<-tmp%*%t(mat)==i
		ids<-which(rowSums(tmp2)==2^(n.var-i))
		tmp<-tmp[ids,]
		if(length(ids)>0){
			mat.in<-rbind(mat.in,tmp)
			for(k in ids)
				list.cover[[length(list.cover)+1]]<-which(tmp2[k,]) #ids2
			mat.names<-matrix(rep(colnames(mat),e=length(ids)),ncol=n.var)
			mat.names[tmp==0]<-""
			mat.names[tmp==-1]<-paste("!",mat.names[tmp==-1],sep="")
			tmp.prime<-apply(mat.names,1,name.paste)
			vec.primes<-c(vec.primes,tmp.prime)
		}
		cover<-unique(unlist(list.cover))
		if(length(cover)==nrow(mat))
			break
	}
	n.prime<-length(vec.primes)
	mat.primes<-matrix(0,nrow(mat),n.prime)
	for(i in 1:n.prime)
		mat.primes[list.cover[[i]],i]<-1
	colnames(mat.primes)<-vec.primes
	mat.primes<-rm.dom(mat.primes,col=TRUE,dom=FALSE)
	vec.primes<-colnames(mat.primes)
	listPI<-list(vec.primes=vec.primes,mat.primes=mat.primes)
	class(listPI)<-"primeImp"
	listPI
}