 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 . 
 The corresponding concept for undirected graphs <a href='drop_aux' title='1'><mark>is</mark></a>a forest , an undirected graph without cycles . Choosing an orientation for a forest <a href='uninflect' title='2'><mark>produces</mark></a> a special kind of directed acyclic graph called a polytree . However <a href='dey_it' title='3'><mark>there</mark></a> are many other kinds of directed acyclic graph <a href='null_relcl' title='4'><mark>that</mark></a>are not formed by orienting the edges of an undirected acyclic graph . Moreover , every undirected graph <a href='got' title='5'><mark>has</mark></a> an acyclic orientation , an assignment of a direction for its edges <a href='null_relcl' title='6'><mark>that</mark></a><a href='uninflect' title='7'><mark>makes</mark></a> it into a directed acyclic graph . To emphasize that DAGs <a href='negative_concord' title='8'><mark>are</mark></a> <a href='negative_concord' title='9'><mark>not</mark></a>the same thing as directed versions of undirected acyclic graphs , some authors call them acyclic directed graphs or acyclic digraphs . 
The corresponding concept fa undirected graphs a forest , an undirected graph without cycles . Choosing an orientation for a forest produce a special kind of directed acyclic graph called a polytree . However it is many other kinds of directed acyclic graph ain't formed by orienting the edges of an undirected acyclic graph . Moreover , every undirected graph got an acyclic orientation , an assignment of a direction ffaits edges make it into a directed acyclic graph . To emphasize that DAGs ain't da same thing as directed versions of undirected acyclic graphs , sum authors call them acyclic directed graphs or acyclic digraphs .