basis now uses sparse matrix instead of zeros.  thermal_dm uses spdiags instead of dense diags
basis now uses sparse matrix instead of zeros.  thermal_dm uses spdiags instead of dense diags

cgranade/qutip,qutip/qutip,cgranade/qutip,anubhavvardhan/qutip,qutip/qutip,zasdfgbnm/qutip,zasdfgbnm/qutip,anubhavvardhan/qutip