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

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Switzerland

dolfim@phys.ethz.ch

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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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