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In April 1942 , five months after the Japanese attack on Pearl Harbor , the unit was activated as part of the 2nd Marine Division . The headquarters was at Camp Elliot in San Diego , California , where it underwent intensive amphibious training . Before being reassigned to the 3rd Marine Division , the unit was assigned to Amphibious Corps , Pacific Fleet . The regiment was sent to Guadalcanal on July 1943 to relieve the 1st Marine Division . 2nd Battalion , 9th Marines participated in the Bougainville campaign of the Solomon Islands in the latter part of 1943 . On July 21 , 1944 , 2 / 9 participated in the invasion of Guam . The Japanese forces staged seven counterattacks , however the Marines prevailed despite the fact that they suffered over 50 % casualties . It was during this initial battle that one Marine , Captain Louis H. Wilson Jr . , ( who would in the future become a Commandant of the Marine Corps ) earned the Medal of Honor .
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The 2nd Battalion , 9th Marines were part of the reserve forces for the Battle of Iwo Jima and were committed to the action five days after D @-@ Day . Among the Marines who distinguished themselves on Iwo Jima was Private Wilson D. Watson who received the Medal of Honor . After the island was secured , the unit was sent back to Guam where they underwent training for a possible invasion of the Japanese mainland . The invasion never occurred since hostilities between Japan and the United States came to an end . The 2nd Battalion , 9th Marines was sent to Camp Pendelton where , in December 1945 , it was once again disbanded .
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= = = Post World War II = = =
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In November 1948 , 2nd Battalion , 9th Marines was again reestablished . The final stages of fighting between the Nationalists and the Communists , in the Chinese Civil War ( also known as the War of Liberation ) , occurred between 1945 and 1950 . When the fighting escalated , the 2nd Battalion , 9th Marines were ordered to Northern China to evacuate all Americans . This mission was accomplished by March 1949 and after which the battalion was sent to Camp Lejeune , North Carolina and was renamed as the 3rd Battalion , 6th Marine .
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On June 25 , 1950 , war broke out between the provisional governments of North and South Korea as they competed for control over the Korean peninsula . North Korea was supported by the People 's Volunteer Army ( PVA ) of the People 's Republic of China and South Korea by the allies under the aegis of the United Nations which included the United States . The conflict is known as the Korean War . The 1st Marine Division was sent in and saw action in the Battle of Chosin Reservoir . In 1952 , 2nd Battalion , 9th Marines was reactivated and underwent training in Japan with the intention of participating in the conflict as part of the 3rd Marine Division . However an armistice was signed on July 27 , 1953 , and the unit did not deploy to Korea . Even though 2nd Battalion , 9th Marines did not actively participate in the conflict , the unit was awarded the Korean Service Streamer and National Defense Service Medal Streamer . The 3rd Marine Divisions headquarters was moved to Okinawa in 1955 and in 1959 the 2nd Battalion , 9th Marines returned to the 1st Marine Division . In 1960 , the battalion returned to the 3rd Marine Division in Okinawa .
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= = = Vietnam War = = =
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The Vietnam War , was a conflict between the Democratic Republic of Vietnam ( DRVN , DRV or North Vietnam ) and the Republic of Vietnam ( RVN or South Vietnam ) , which eventually involved their respective allies . In 1959 , the United States sent military advisors to train the Army of the Republic of Vietnam . By 1965 , there were 25 @,@ 000 military advisors in South Vietnam and on March 8 , 1965 , the United States Marines became the first US combat troops to land in South Vietnam , with a force of 3 @,@ 500 .
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The 3d Marine Division began operating in Vietnam when on March 6 , 1965 , they opened a Marine Compound at the Da Nang Air Base . On July 4 , 1965 , 2nd Battalion , 9th Marines were ordered to Vietnam from Okinawa . 2nd Battalion , 9th Marines fought battles in or around Danang , Hue , Phu Bai , Đông Hà , Camp Carroll , Cam Lộ , Con Thien , Than Cam Son , Quảng Trị , Cửa Việt , Vandegrift Combat Base and what is considered by many as their most vicious engagement , the Battle of Khe Sanh .
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In September 1962 , U.S. military forces constructed an airstrip outside the town of Khe Sanh which became known as the Khe Sanh Combat Base . In 1965 the U.S. Special Forces constructed a base next to it . The base 's defense was codenamed Operation Scotland and manned by the 2nd Battalion , 9th Marines from 1967 . It was used as a staging ground for a number of attacks on North Vietnamese ( NVA ) troop movements down the Ho Chi Minh Trail .
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From April to June 1966 , the 2 / 9 Marines were caught in crossfire of the Buddhist Uprising , when much of the forces of I Corps rebelled against Prime Minister and Air Marshal Nguyen Cao Ky , the head of the ruling junta , who had dismissed their commander , General Nguyen Chanh Thi .
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In April and May 1967 various " Hill Fights " on Hills 861 , 881 North and 881 South between the 2 / 9 Marines and NVA occurred . In January 1968 , Khe Sanh Combat Base came under heavy attack in what is known as the Battle of Khe Sanh . The main objective of the Communists was to draw off American troops into the countryside in preparation for the Tet Offensive . Despite being outnumbered , 2nd Battalion , 9th Marines held their ground and the North Vietnamese were driven off of the area around after experiencing heavy casualties by heavy aerial bombardments by B @-@ 52s .
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From January 22 to March 18 , 1969 , 2 / 9 participated in Operation Dewey Canyon which was a sweep of the A Shau Valley and the last major offensive by the Marine Corps in Vietnam .
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In August 1969 , 2nd Battalion , 9th Marines was ordered to return to Camp Schwab , Okinawa . During this period the unit was assigned to sea duty in and around the waters of Vietnam and continued to receive combat training at Camp Fuji , Japan and Subic Bay in the Philippines .
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= = = = Mayaguez Incident = = = =
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On May 12 , 1975 , barely two weeks after the fall of Saigon , Khmer Rouge forces seized a U.S. flagged merchant ship , the SS Mayaguez in recognized international sea lanes claimed as territorial waters by Cambodia and removed its crew for questioning . The Khmer Rouge naval forces used abandoned US Navy " Swift Boats " in the seizure of the U.S. container ship .
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Calling the seizure " piracy " , President Ford ordered a military response to retake the ship and its 39 @-@ man crew , mistakenly thought to be on Koh Tang Island . On May 13 , two A @-@ 7D Corsairs saw the 39 man crew board a fishing boat and saw people disembarking fishing boats at Koh Tang Island . They assumed that the Mayaguez crew was on the island . Elements of the 1st Battalion , 4th Marines , the 2nd Battalion , 4th Marines , and the 2nd Battalion , 9th Marines , were flown to an advanced staging of a joint US Task Force . On May 14 , the Marines from Company D , 1st Battalion , 4th Marines boarded the Mayaguez only to find it deserted and raised the American flag . A Thai fishing boat with a Thai crew and the 39 crew members of the SS Mayaguez which had been set free , approached the USS Wilson .
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= = = = Battle of Koh Tang Island = = = =
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2nd Battalion , 9th Marines landed on Koh Tang Island where the crew of the SS Mayaguez was believed to be held , they were unaware that the crew was already in American hands . The Marines and the CH @-@ 53 helicopters which transported them , were attacked by the Khmer Rouge with machine guns , mortars , and rocket propelled grenade launchers in what became known as the Battle of Koh Tang Island . When the battalion received word of the safe arrival of the Mayaguez crew on the USS Wilson the Marines planned their withdrawal once they received orders from the U.S. Joint Chiefs of Staff to that effect . After the last helicopter left , a head count showed that 3 Marines were left behind on the island . They were : PFC Gary Hall , LCpl . Joseph Hargrove , and Pvt Danny Marshall from E CO , 2nd Battalion , 9th Marines . The three Marines were captured by the Khmer Rouge within a few days , tortured , executed , and buried in a common , unmarked grave on Koh Tang Island .
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The Mayagüez incident with the Khmer Rouge , which ended on May 15 , 1975 , marked the last official battle of the 2nd Battalion , 9th Marines in the Vietnam War . The unit deployment program was put into practice in February 1979 , and 2nd Battalion , 9th Marines became the first battalion to rotate to the United States . A total of 18 Marines were killed on the last day of the SS Mayaguez rescue operation . They are the last Marines listed on the timeline of the Vietnam Veterans Memorial located in Washington , D.C.
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= = = Post Vietnam era = = =
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= = = = Operations Desert Shield & Desert Storm = = = =
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Before the August 2 , 1990 , invasion of Kuwait by Saddam Hussein 's Iraqi forces , 2nd Battalion , 9th Marines was deployed to Okinawa , Japan as part of the Unit Deployment Program . In October 1990 the unit deployed to the Republic of the Philippines where it became the Ground Combat Element of Marine Air @-@ Ground Task Force ( MAGTF ) 4 @-@ 90 . On November 1990 , the island of Cebu , a Philippine providence , was devastated by a typhoon . Members of the battalion provided assistance during the disaster relief efforts . The Battalion remained in the Philippines until April 1991 when it returned to Okinawa , Japan . Subsequently the Battalion returned to Camp Pendleton in August 1991 .
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= = = = Operation " Restore Hope " = = = =
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The 5th Marine Regiment designated 2 / 9 to participate in the Marine Expeditionary Unit deployment cycle during November 1991 . With the successful culmination of the Special Operations Capable Exercise ( SOCEX ) , 2nd Battalion , 9th Marines became the designated Battalion Landing Team ( BLT ) for the 15th Marine Expeditionary Unit ( 15th MEU ) .
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During this period , there were two main factions in the Republic of Somalia who provoked an all out war which became known as the Somalian Civil War . One of the factions was led by Ali Mahdi Mohamed , who became president ; and the other , by the warlord Mohammed Farah Aidid .
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In 1991 , the United States initiated Operation Provide Relief ( UNOSOM I ) which was part of a United Nations ( UN ) endorsed effort called The Unified Task Force ( UNITAF ) , to provide humanitarian relief . In August 1992 , President George H. Bush sent , 25 @,@ 000 US troops ( mostly US Marines from I MEF ) to the Republic of Somalia and the mission was renamed Operation Restore Hope , also known as UNOSOM II . Its main objectives were to provide humanitarian relief , initiate ' nation building ' , disarm the various factions , restore law and order , help the people set up a representative government , and restore the infrastructure .
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That same month , 2nd Battalion , 9th Marines was deployed to Somalia . BLT 2 / 9 's mission as the lead unit , was to secure the port and airfield in Mogadishu which allowed the rapid build @-@ up of forces in @-@ country . The mission was accomplished between December 9 , 1992 and February 1993 . The Somalis referred to Marines of 2nd Battalion , 9th Marines as The Black Boots . On January 30 , 1993 , a Marine patrol was ambushed in Mogadishu by gunmen faithful to warlord Mohammed Farah Aidid bringing about casualties . 2 / 9 remained in Somalia until April 1993 when they returned to Camp Pendleton . The battalions next two deployments were to Fort Sherman , Panama during one of which they participated in the Javelin anti @-@ tank missile evaluation program . On September 2 , 1994 , 2nd Battalion 9th Marines was deactivated and redesignated 2nd Battalion 4th Marines .
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= = = 2000 @-@ present = = =
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On December 7 , 2006 , Headquarters Marine Corps released a message stating that 2nd Battalion 9th Marines would be reactivated during 2007 as part of the continuing Global War on Terror . 2nd Battalion 9th Marines was re @-@ activated on July 13 , 2007 and replaced the Anti @-@ Terrorism Battalion ( ATBn ) . In September 2008 , Marines and Sailors from 2 / 9 deployed to Al Anbar Province in support of Operation Iraqi Freedom . They were based in the city of Ramadi and returned in April 2009 without any Marines or Sailors killed in action . July 2010 Marines and Sailors from 2 / 9 deployed to Marjah , Helmand Province , Afghanistan in support of Operation Enduring Freedom . In December 2010 Echo Company from 2 / 9 were attached to 3 / 5 in Sangin , Afghanistan where they earned the notorious nickname of " Green Hats . " They returned February 2011 . They redeployed back to Marjah December 2011 and returned July 2012 . Echo and Weapons companies deployed once more to Afghanistan from January through April 2013 , participating in combat operations out of Camp Leatherneck . On April 1 , 2015 the battalion was deactivated in a ceremony at Camp Lejeune .
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= = Medal of Honor recipients = =
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The Medal of Honor is the highest military decoration awarded by the United States . It is bestowed on a member of the United States armed forces who distinguishes himself or herself " ... conspicuously by gallantry and intrepidity at the risk of his life above and beyond the call of duty while engaged in an action against an enemy of the United States ... " . The following table contains the names of the men who were recipients of the Medal of Honor while serving in 2 / 9 . They are listed in accordance to the " Date of Action " in which the MoH citation was made . † indicates that the Medal of Honor was awarded posthumously
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= = Commandants of the Marine Corps = =
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The Commandant of the United States Marine Corps is the highest @-@ ranking officer of the United States Marine Corps and a member of the Joint Chiefs of Staff , reporting to the Secretary of the Navy but not to the Chief of Naval Operations . Three Marines who served in 2nd Battalion 9th Marines became Commandant of the Marine Corps . They are listed in the table in accordance to the years in which they served as Commandants and their ranks are those which they held while serving in 2 / 9 , they were :
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= = Distinguished Marines = =
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Other Marines who served in the 2nd Battalion 9th Marines during their careers , who subsequently distinguished themselves by either becoming a general officer ( O @-@ 7 and above ) or recipients of the Medal of Honor while assigned to a different unit were :
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= = Other notable former members = =
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Bing West , served in the mortar platoon during the Vietnam War in 1965 .
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= = Unit awards = =
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A unit citation or commendation is an award bestowed upon an organization for the action cited . Members of the unit who participated in said actions are allowed to wear on their uniforms the awarded unit citation . 2 / 9 has been presented with the following awards :
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= Directed acyclic graph =
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In mathematics and computer science , a directed acyclic graph ( DAG / ˈdæɡ / ) , is a finite directed graph with no directed cycles . That is , it consists of finitely many vertices and edges , with each edge directed from one vertex to another , such that there is no way to start at any vertex v and follow a consistently @-@ directed sequence of edges that eventually loops back to v again . Equivalently , a DAG is a directed graph that has a topological ordering , a sequence of the vertices such that every edge is directed from earlier to later in the sequence .
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DAGs may be used to model many different kinds of information . The reachability relation in a DAG forms a partial order , and any finite partial order may be represented by a DAG using reachability . The program evaluation and review technique uses DAGs to model the milestones and activities of large human projects , and schedule these projects to use as little total time as possible . Scheduling of computer operations such as the updates to a spreadsheet or the compilation operations in a makefile can also be performed using topological orderings of DAGs . Combinational logic blocks in electronic circuit design , and the operations in dataflow programming languages , involve acyclic networks of processing elements . DAGs can also represent collections of events and their influence on each other , either in a probabilistic structure such as a Bayesian network or as a record of historical data such as family trees or the version histories of distributed revision control systems . DAGs can also be used as a compact representation of sequence data , such as the directed acyclic word graph representation of a collection of strings , or the binary decision diagram representation of sequences of binary choices .
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Important polynomial time computational problems on DAGs include topological sorting ( finding a topological ordering ) , construction of the transitive closure and transitive reduction ( the largest and smallest DAGs with the same reachability relation , respectively ) , and the closure problem , in which the goal is to find a minimum @-@ weight subset of vertices with no edges connecting them to the rest of the graph . Transforming a directed graph with cycles into a DAG by deleting as few vertices or edges as possible ( the feedback vertex set and feedback edge set problem , respectively ) is NP @-@ hard , but any directed graph can be made into a DAG ( its condensation ) by contracting each strongly connected component into a single supervertex . The problems of finding shortest paths and longest paths can be solved on DAGs in linear time , in contrast to arbitrary graphs for which shortest path algorithms are slower and longest path problems are NP @-@ hard .
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The corresponding concept for undirected graphs is a forest , an undirected graph without cycles . Choosing an orientation for a forest produces a special kind of directed acyclic graph called a polytree . However there are many other kinds of directed acyclic graph that are not formed by orienting the edges of an undirected acyclic graph . Moreover , every undirected graph has an acyclic orientation , an assignment of a direction for its edges that makes it into a directed acyclic graph . To emphasize that DAGs are not the same thing as directed versions of undirected acyclic graphs , some authors call them acyclic directed graphs or acyclic digraphs .
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= = Definitions = =
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A graph is formed by a collection of vertices and edges , where the vertices are structureless objects that are connected in pairs by edges . In the case of a directed graph , each edge has an orientation , from one vertex to another vertex . A path in a directed graph can be described by a sequence of edges having the property that the ending vertex of each edge in the sequence is the same as the starting vertex of the next edge in the sequence ; a path forms a cycle if the starting vertex of its first edge equals the ending vertex of its last edge . A directed acyclic graph is a directed graph that has no cycles .
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A vertex v of a directed graph is said to be reachable from another vertex u when there exists a path that starts at u and ends at v. As a special case , every vertex is considered to be reachable from itself ( by a path with zero edges ) . If a vertex can reach itself via a nontrivial path ( a path with one or more edges ) , then that path is a cycle , so another way to define directed acyclic graphs is that they are the graphs in which no vertex can reach itself via a nontrivial path .
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A topological ordering of a directed graph is an ordering of its vertices into a sequence , such that for every edge the start vertex of the edge occurs earlier in the sequence than the ending vertex of the edge . A graph that has a topological ordering cannot have any cycles , because the edge into the earliest vertex of a cycle would have to be oriented the wrong way . Therefore , every graph with a topological ordering is acyclic . Conversely , every directed acyclic graph has a topological ordering . Therefore , this property can be used as an alternative definition of the directed acyclic graphs : they are exactly the graphs that have topological orderings .
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= = Mathematical properties = =
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= = = Reachability , transitive closure , and transitive reduction = = =
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The reachability relationship in any directed acyclic graph can be formalized as a partial order ≤ on the vertices of the DAG . In this partial order , two vertices u and v are ordered as u ≤ v exactly when there exists a directed path from u to v in the DAG ; that is , when v is reachable from u . However , different DAGs may give rise to the same reachability relation and the same partial order . For example , the DAG with two edges a → b and b → c has the same reachability relation as the graph with three edges a → b , b → c , and a → c . Both of these DAGS produce the same partial order , in which the vertices are ordered as a ≤ b ≤ c .
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If G is a DAG , its transitive closure is the graph with the most edges that represents the same reachability relation . It has an edge u → v whenever u can reach v. That is , it has an edge for every related pair u ≤ v of distinct elements in the reachability relation of G , and may therefore be thought of as a direct translation of the reachability relation ≤ into graph @-@ theoretic terms . The same method of translating partial orders into DAGs works more generally : for every finite partially ordered set ( S , ≤ ) , the graph that has a vertex for each member of S and an edge for each pair of elements related by u ≤ v is automatically a transitively closed DAG , and has ( S , ≤ ) as its reachability relation . In this way , every finite partially ordered set can be represented as the reachability relation of a DAG .
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The transitive reduction of a DAG G is the graph with the fewest edges that represents the same reachability relation as G. It is a subgraph of G , formed by discarding the edges u → v for which G also contains a longer path connecting the same two vertices . Like the transitive closure , the transitive reduction is uniquely defined for DAGs . In contrast , for a directed graph that is not acyclic , there can be more than one minimal subgraph with the same reachability relation .
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If a DAG G has a reachability relation described by the partial order ≤ , then the transitive reduction of G is a subgraph of G that has an edge u → v for every pair in the covering relation of ≤ . Transitive reductions are useful in visualizing the partial orders they represent , because they have fewer edges than other graphs representing the same orders and therefore lead to simpler graph drawings . A Hasse diagram of a partial order is a drawing of the transitive reduction in which the orientation of each edge is shown by placing the starting vertex of the edge in a lower position than its ending vertex .
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= = = Topological ordering = = =
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Every directed acyclic graph has a topological ordering , an ordering of the vertices such that the starting endpoint of every edge occurs earlier in the ordering than the ending endpoint of the edge . The existence of such an ordering can be used to characterize DAGs : a directed graph is a DAG if and only if it has a topological ordering . In general , this ordering is not unique ; a DAG has a unique topological ordering if and only if it has a directed path containing all the vertices , in which case the ordering is the same as the order in which the vertices appear in the path .
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The family of topological orderings of a DAG is the same as the family of linear extensions of the reachability relation for the DAG , so any two graphs representing the same partial order have the same set of topological orders .
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= = = Combinatorial enumeration = = =
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The graph enumeration problem of counting directed acyclic graphs was studied by Robinson ( 1973 ) . The number of DAGs on n labeled vertices , for n = 0 , 1 , 2 , 3 , … ( without restrictions on the order in which these numbers appear in a topological ordering of the DAG ) is
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1 , 1 , 3 , 25 , 543 , 29281 , 3781503 , … ( sequence A003024 in the OEIS ) .
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These numbers may be computed by the recurrence relation
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