tridiag divide and conquer (D&C) routines

Collaboration diagram for tridiag divide and conquer (D&C) routines:

Topics
	laed0: D&C step: top level solver
	laed1: D&C step: merge subproblems
	laed2: D&C step: deflation
	laed3: D&C step: secular equation
	laed4: D&C step: secular equation nonlinear solver
	laed5: D&C step: secular equation, 2x2
	laed6: D&C step: secular equation Newton step
	lamrg: permutation to merge 2 sorted lists
	— eig value only or update Q —
	laed7: D&C step: merge subproblems
	laed8: D&C step: deflation
	laed9: D&C step: secular equation
	laeda: D&C step: z vector

Detailed Description