note

As of Sep 9,
 in the main shift-and-invert function, removed all instances of energy related checks. This includes modifying the !measure function
First iteration of trial runs. Strictly solving H|psi> = |phi>. Only calculates energy when the calculation converges.

Program can get past linsolve,
MethodError: Cannot `convert` an object of type Float64 to an object of type ITensor
Noted on Krylov method: Input type linear map: AbstractMatrix <=> AbstractMPS

Sep 12
Cleaned the main loop (Two iterations: linsolve until convergeance tol, (inner iteration), H|psi> = |phi>, then repeat until largest eigenvalue obtained (outer loop))
Compare to eigsolve, return Vector{Itensor}, correct code since linsolve only returns one object instead of vector 
Measure! function type mismatch

Sep 14
Remove the original dependency on the DMRGobserver. As of now the code only works with no explicit 'observer' variable.
Modified checkdone! and measure!. Now both does nothing when observer is not defined

New error in the replacebond! function:
 LoadError: ArgumentError: Trying to perform the eigendecomposition of a matrix containing NaNs or Infs
Check symptoms: occurs at sweep 3

ITensor logic: the main function takes in H, and psi, creates object ProjMPO PH, pass it to main work function

position! function invokes makeL! and makeR!

Sep 21
test the behavior of position! functions. Since there are no explicit return behavior on makeL! and _makeL!, will modify
Dim mismatch in linsolve. Test removing initial guess