added DD model
added DD model

RMKD/networkx,debsankha/networkx,chrisnatali/networkx,farhaanbukhsh/networkx,nathania/networkx,jni/networkx,nathania/networkx,ghdk/networkx,debsankha/networkx,bzero/networkx,dmoliveira/networkx,kernc/networkx,chrisnatali/networkx,yashu-seth/networkx,kernc/networkx,dmoliveira/networkx,wasade/networkx,ltiao/networkx,jni/networkx,jakevdp/networkx,ionanrozenfeld/networkx,farhaanbukhsh/networkx,jakevdp/networkx,tmilicic/networkx,aureooms/networkx,kernc/networkx,ghdk/networkx,NvanAdrichem/networkx,harlowja/networkx,sharifulgeo/networkx,SanketDG/networkx,debsankha/networkx,sharifulgeo/networkx,RMKD/networkx,aureooms/networkx,RMKD/networkx,ionanrozenfeld/networkx,chrisnatali/networkx,harlowja/networkx,bzero/networkx,aureooms/networkx,michaelpacer/networkx,jakevdp/networkx,nathania/networkx,blublud/networkx,cmtm/networkx,bzero/networkx,beni55/networkx,ionanrozenfeld/networkx,jni/networkx,dhimmel/networkx,sharifulgeo/networkx,dhimmel/networkx,dhimmel/networkx,harlowja/networkx,jfinkels/networkx,JamesClough/networkx,dmoliveira/networkx,OrkoHunter/networkx,jcurbelo/networkx,andnovar/networkx,farhaanbukhsh/networkx,ghdk/networkx,Sixshaman/networkx,goulu/networkx,blublud/networkx,blublud/networkx