Modifies is_diagonal to remove check for square.
Modifies is_diagonal to remove check for square.

Non-square matrices can also be diagonal now. For square diagonal matrices, user will have to check for diagonal and square both.

farhaanbukhsh/sympy,lindsayad/sympy,kevalds51/sympy,debugger22/sympy,skirpichev/omg,toolforger/sympy,aktech/sympy,souravsingh/sympy,Curious72/sympy,garvitr/sympy,flacjacket/sympy,yashsharan/sympy,oliverlee/sympy,ahhda/sympy,meghana1995/sympy,toolforger/sympy,madan96/sympy,shikil/sympy,MechCoder/sympy,jaimahajan1997/sympy,debugger22/sympy,hrashk/sympy,Arafatk/sympy,atreyv/sympy,kevalds51/sympy,atreyv/sympy,hargup/sympy,kmacinnis/sympy,wanglongqi/sympy,farhaanbukhsh/sympy,MridulS/sympy,AkademieOlympia/sympy,jbbskinny/sympy,abloomston/sympy,sunny94/temp,dqnykamp/sympy,MridulS/sympy,sahmed95/sympy,Arafatk/sympy,lidavidm/sympy,Mitchkoens/sympy,Shaswat27/sympy,ChristinaZografou/sympy,jerli/sympy,dqnykamp/sympy,kaichogami/sympy,Davidjohnwilson/sympy,iamutkarshtiwari/sympy,yukoba/sympy,lidavidm/sympy,postvakje/sympy,minrk/sympy,ahhda/sympy,pandeyadarsh/sympy,liangjiaxing/sympy,Sumith1896/sympy,sampadsaha5/sympy,vipulroxx/sympy,grevutiu-gabriel/sympy,debugger22/sympy,jbbskinny/sympy,iamutkarshtiwari/sympy,Sumith1896/sympy,rahuldan/sympy,liangjiaxing/sympy,Shaswat27/sympy,kaushik94/sympy,amitjamadagni/sympy,Mitchkoens/sympy,shipci/sympy,sahilshekhawat/sympy,yukoba/sympy,chaffra/sympy,atreyv/sympy,atsao72/sympy,garvitr/sympy,souravsingh/sympy,bukzor/sympy,jbbskinny/sympy,cswiercz/sympy,ga7g08/sympy,cswiercz/sympy,mcdaniel67/sympy,Vishluck/sympy,chaffra/sympy,ChristinaZografou/sympy,abhiii5459/sympy,kevalds51/sympy,sahilshekhawat/sympy,kumarkrishna/sympy,jamesblunt/sympy,Mitchkoens/sympy,asm666/sympy,sunny94/temp,maniteja123/sympy,pandeyadarsh/sympy,maniteja123/sympy,saurabhjn76/sympy,emon10005/sympy,souravsingh/sympy,cccfran/sympy,cswiercz/sympy,vipulroxx/sympy,mcdaniel67/sympy,kumarkrishna/sympy,abhiii5459/sympy,shikil/sympy,AunShiLord/sympy,jamesblunt/sympy,Vishluck/sympy,meghana1995/sympy,jaimahajan1997/sympy,Curious72/sympy,shipci/sympy,yukoba/sympy,abhiii5459/sympy,skidzo/sympy,bukzor/sympy,kaushik94/sympy,lindsayad/sympy,hrashk/sympy,AkademieOlympia/sympy,Gadal/sympy,madan96/sympy,oliverlee/sympy,hargup/sympy,moble/sympy,chaffra/sympy,jerli/sympy,kaichogami/sympy,srjoglekar246/sympy,skidzo/sympy,lindsayad/sympy,beni55/sympy,MechCoder/sympy,farhaanbukhsh/sympy,postvakje/sympy,yashsharan/sympy,ahhda/sympy,asm666/sympy,garvitr/sympy,dqnykamp/sympy,drufat/sympy,saurabhjn76/sympy,hargup/sympy,toolforger/sympy,Curious72/sympy,pbrady/sympy,jaimahajan1997/sympy,moble/sympy,kmacinnis/sympy,sahmed95/sympy,jerli/sympy,liangjiaxing/sympy,pandeyadarsh/sympy,diofant/diofant,shipci/sympy,lidavidm/sympy,AunShiLord/sympy,iamutkarshtiwari/sympy,emon10005/sympy,wanglongqi/sympy,atsao72/sympy,sunny94/temp,Designist/sympy,pbrady/sympy,drufat/sympy,VaibhavAgarwalVA/sympy,beni55/sympy,mafiya69/sympy,drufat/sympy,bukzor/sympy,sampadsaha5/sympy,minrk/sympy,cccfran/sympy,madan96/sympy,Titan-C/sympy,asm666/sympy,kmacinnis/sympy,AunShiLord/sympy,moble/sympy,yashsharan/sympy,wyom/sympy,sahmed95/sympy,rahuldan/sympy,Davidjohnwilson/sympy,skidzo/sympy,MridulS/sympy,Gadal/sympy,vipulroxx/sympy,sampadsaha5/sympy,emon10005/sympy,Gadal/sympy,kaushik94/sympy,aktech/sympy,grevutiu-gabriel/sympy,wyom/sympy,grevutiu-gabriel/sympy,MechCoder/sympy,VaibhavAgarwalVA/sympy,Shaswat27/sympy,oliverlee/sympy,Designist/sympy,Designist/sympy,pbrady/sympy,amitjamadagni/sympy,saurabhjn76/sympy,mafiya69/sympy,meghana1995/sympy,kaichogami/sympy,Arafatk/sympy,cccfran/sympy,postvakje/sympy,maniteja123/sympy,kumarkrishna/sympy,abloomston/sympy,shikil/sympy,beni55/sympy,AkademieOlympia/sympy,ga7g08/sympy,atsao72/sympy,Titan-C/sympy,sahilshekhawat/sympy,jamesblunt/sympy,abloomston/sympy,VaibhavAgarwalVA/sympy,wyom/sympy,ga7g08/sympy,ChristinaZografou/sympy,Davidjohnwilson/sympy,hrashk/sympy,aktech/sympy,wanglongqi/sympy,mcdaniel67/sympy,mafiya69/sympy,rahuldan/sympy,Titan-C/sympy,Sumith1896/sympy,Vishluck/sympy