Never mind, I solved the problem. I post the answer here just in case anyone else gets stuck on such a detail like me.
In the site basis, you simply define an operator with the same name but with some dummy value. For example, in the site basis of a boson:
<OPERATOR name="Sz" matrixelement="1"/>?
It is now safe to measure Sz on all sites (and discard the value on the bosonic sites).
If there is a way in ALPS to do this without a hack, I would be pleased to know!
/Axel
________________________________ Från: Comp-phys-alps-users comp-phys-alps-users-bounces@lists.phys.ethz.ch för Axel Gagge axel.gagge@fysik.su.se Skickat: den 9 maj 2017 17:58 Till: comp-phys-alps-users Ämne: [ALPS-users] DMRG measurements of observables with support only on some lattice sites
Hello all,
I am working with DMRG for a model where the unit cell consists of two lattice sites of different types (one is a boson mode while the other is a two-level/spin 1/2). Now, I want to measure say the expectation value <Sz> of my ground state on all the spin sites - how can I do this in ALPS? If I use MEASURE_LOCAL, ALPS tries to compute the expectation value of Sz for the boson sites and crashes.
MEASURE_LOCAL_AT seems like the reasonable thing to work with, but does it also work for expectation values?
Best regards,
Axel