If the measurement operator is unitary, the return values will be just the real part.

Best,
Michele


On 19 Mar 2017, at 17:30, Robertson Esperanza <robbie.esperanza@gmail.com> wrote:

Just a quick question, using MEASURE_HALF_CORRELATIONS returns real values, is it the real part, the imaginary part, or the complex amplitude of the correlation function? Thank you for the help.

On Wed, Feb 8, 2017 at 4:50 PM, Julien <julien.despres@institutoptique.fr> wrote:

The operator defined in the 'sitebasis' of a Hamiltonian is only valid for this Hamiltonian which is not the case when you define it as a 'siteoperator'. You can use it for different models at the condition that the operators that you use inside this function are defined in the corresponding 'sitebasis'. And one more thing, your function for the magnetization 'diag_mag_correct' is not correct from what has been said previously. 

Julien


On 08/02/2017 00:56, Robertson Esperanza wrote:
I see, so you defined the operator under the SITEBASIS. I thought it would work if you define it, as suggested on the earlier replies, as a site operator. I don't know the difference though, thank you for the help.

On Wed, Feb 8, 2017 at 3:04 AM, julien <julien.despres@institutoptique.fr> wrote:
I forgot the corresponding python script ...


On 07/02/2017 17:04, Robertson Esperanza wrote:
Yes, it is intended when I attached it, so it can be changed. When i run the script, I put the filepath, but I still get the x = [0], y = [0] result. Can I see what's the result when you run the script? Thank you for the help.

On Tue, Feb 7, 2017 at 6:53 PM, Julien <julien.despres@institutoptique.fr> wrote:

yes, there is no path ...

Julien


On 07/02/2017 09:53, Robertson Esperanza wrote:
the line where I put the file path of the xml file (i.e. 'MODEL_LIBRARY':) ? 

On Tue, Feb 7, 2017 at 4:04 PM, Julien <julien.despres@institutoptique.fr> wrote:

I tested your file after modifying this line. It works

On 07/02/2017 09:01, Julien wrote:

Hi,

there is a little problem in your python script; have a look to the line where you include the xml file for the models.

Julien


- 
__________________________________

DESPRES Julien
Ph.D. student

Center for Theoretical Physics
Quantum Matter Theory team
Ecole Polytechnique
91128 Palaiseau Cedex
France, EU
Office : 00.10.06 (ground floor)
Phone : +33 1 64 33 42 81

Laboratoire Charles Fabry
Atom Optics group
Institut d'Optique Graduate School
2 Avenue Augustin Fresnel
91127 Palaiseau Cedex
France, EU
Office : R2.29 (1st floor)
Phone: +33 1 64 53 33 49
__________________________________
On 07/02/2017 04:24, Robertson Esperanza wrote:
I tried to print the result of taking the local measurement for n_i^2 but it only shows
x = [0], y = [0], instead of x = [0 1 2 3 4 5 6 7 8 9], y = [10 scalar values] (since i'm using a 10-site open chain). I attached my python script and mymodels.xml. Thank you for the help.
On Mon, Feb 6, 2017 at 4:29 PM, Julien <julien.despres@institutoptique.fr> wrote:

Hi,

you can do it in this way but in your parameter file you have to write :

model['MODEL_LIBRARY'] = 'my_own_models.xml'

or you can put it wherever you want but in this case : model['MODEL_LIBRARY'] = 'path_to_the_xml_file' Julien
On 06/02/2017 09:21, Robertson Esperanza wrote:
When creating a new model file, is it necessary that the new model file be saved on the same folder of the default models.xml file?
On Mon, Feb 6, 2017 at 3:55 PM, Michele Dolfi <dolfim@phys.ethz.ch> wrote:
MEASURE_AVERAGE is compute the average among all sites, i.e. a scalar value.
MEASURE_LOCAL returns a list of measurements on all sites.
Best,
Michele
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On 6 Feb 2017, at 08:50, Robertson Esperanza <robbie.esperanza@gmail.com> wrote:
Oh, I forgot to mention that I'm using mps_optim application. How does the result of MEASURE_AVERAGE differ from MEASURE_LOCAL, if let's say I use "n" for these parameters? Thanks
On Mon, Feb 6, 2017 at 3:08 PM, Michele Dolfi <dolfim@phys.ethz.ch> wrote:
Hello,
Could you please be a bit more specific about the application you are running?
You are right about the local measurement, but you need MEASURE_LOCAL, since you want to value at each site. Since the n_i^2 operator is not yet defined in the model library, you need to add it yourself. Basically I would do as follow:
1. Copy the file models.xml from ALPS_ROOT/lib/xml/models.xml, where ALPS_ROOT is the root location of your alps installation.
2. Add this definition to your local copy, it defines the n^2 operator
<SITEOPERATOR name=“n_squared" site="x">   n(x)*n(x) </SITEOPERATOR>
3. In your input parameters you have now to link to your new model file.
MODEL_LIBRARY=“path/to/models.xml”
4. And add your measurement
MEASURE_LOCAL[Density^2] = “ n_squared"
Hope this helps.
Best,
Michele
--
ETH Zurich
Dr. Michele Dolfi
Institute for Theoretical Physics
HIT G 32.4
Wolfgang-Pauli-Str. 27
8093 Zurich
Switzerland
On 6 Feb 2017, at 07:26, Robertson Esperanza <robbie.esperanza@gmail.com> wrote:
Hello, I only started studying many-body physics, so there might be gaps in my knowledge. When using the MEASURE_CORRELATION, why does the measurement goes for only site i<j, is it because there will be "blowing up"? Alternatively, to measure for i=j, i think I could use MEASURE_AVERAGE, of let's say (n_i)^2 where n - n_up + n_down. How could I define such measurement, where you use an operator successively? Thank you for replying
Robertson Esperanza
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Atom Optics group
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Ecole Polytechnique
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France, EU
Office : 00.10.06 (ground floor)
Phone : +33 1 64 33 42 81

Laboratoire Charles Fabry
Atom Optics group
Institut d'Optique Graduate School
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France, EU
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Phone: +33 1 64 53 33 49
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Phone : +33 1 64 33 42 81

Laboratoire Charles Fabry
Atom Optics group
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Phone: +33 1 64 53 33 49
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Phone : +33 1 64 33 42 81

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