On Dec 19, 2008, at 11:58 PM, Cezary Sliwa wrote:
From http://alps.comp-phys.org/mediawiki-1.9.3/index.php/Tutorials:ModelHOWTO
"Optionally, a type attribute can be set to bosonic (the default) or fermionic. It should be set to fermionic when the quantum number is a fermionic number operator. This information will be used when determining commutation relation between operators on different sites."
This is very imprecise. To be honest, I do not understand that at all.
First of all, good quantum numbers take numerical values, and numbers commute. Hence, the relations for quantum numbers are always *commutation* relations.
The anticommutation relations are for the creation and annihilation *operators*. Hence, whether or not it make sense to assign such a "type=" attribute to a degree of freedom (call it a QUANTUMNUMBER), the attribute applies to *operators*! Moreover, not all operators, but only those that are odd in the creation and annihilation operators. For example, the spin operator for a pair of spin-up, spin-down fermion states satisfies *commutation* relations.
Indeed you are right. What we mean is that a "fermionic" quantum number is a quantum number describing the number of fermions on a site. Knowing that a quantum number counts the number of fermions allows us to automatically deduce which operators are "fermionic" in the sense that you mention: they change these fermion numbers by an odd number.
Now please tell me why the code refuses to generate a matrix (probably for the hopping and exchange terms, but the error message does not state which terms pose a problem). Both terms are even in the creation and annihilation operators (capital S refers to a bosonic spin):
What is the error message and what is the code?
Matthias