construct a linked list from 2d matrix in ruby

Ruby program for construct a linked list from 2d matrix. Here problem description and explanation.

#  Ruby program for
#  Construct a linked list from 2D matrix
class LinkNode 
	# Define the accessor and reader of class LinkNode
	attr_reader :data, :next, :down
	attr_accessor :data, :next, :down
	def initialize(data) 
		self.data = data
		self.next = nil
		self.down = nil
	end

end

class DoublyLinkedList 
	# Define the accessor and reader of class DoublyLinkedList
	attr_reader :head
	attr_accessor :head
	def initialize() 
		self.head = nil
	end

	def display() 
		if (self.head == nil) 
			print("Empty linked list")
		else
 
			front = self.head
			right = nil
			while (front != nil) 
				right = front
				while (right != nil) 
					print(right.data ,"  ")
					right = right.next
				end

				print("\n")
				#  Visit to down node
				front = front.down
			end

		end

	end

	def insertData(matrix, rows, cols) 
		#  Some auxiliary variables
		levelHead = nil
		root = nil
		perv = nil
		i = 0
		j = 0
		#  Add first row elements into result list 
		while (i < cols) 
			if (self.head == nil) 
				#  Add first node
				self.head = LinkNode.new(matrix[0][i])
				levelHead = self.head
			else
				#  next head
				levelHead.next = LinkNode.new(matrix[0][i])
				levelHead = levelHead.next
			end
			i += 1
		end

		#  Get first element    
		levelHead = self.head
		i = 1
		#  Add all the bottom element of each column
		while (i < rows) 
			root = nil
			perv = root
			while (j < cols) 
				levelHead.down = LinkNode.new(matrix[i][j])
				if (root == nil) 
					root = levelHead.down
					perv = root
				else
 
					perv.next = levelHead.down
					perv = levelHead.down
				end

				levelHead = levelHead.next
				j += 1
			end

			levelHead = root
			#  reset col
			j = 0
			#  change row
			i += 1
		end

	end

end

def main() 
	dll = DoublyLinkedList.new()
	#  Create 2D metrix
	matrix = [
		[1, 6, 9, 2, -9],
		[2, 5, -5, 7, 1],
		[3, 4, 1, 8, 2]
	]
	rows = matrix.length
	cols = matrix[0].length
	dll.insertData(matrix, rows, cols)
	dll.display()
end

main()

Output

1  6  9  2  -9  
2  5  -5  7  1  
3  4  1  8  2