- Comp-phys-alps-users - lists.phys.ethz.ch

Printing out Eigenvector
by rexlundgren＠mail.utexas.edu 05 Sep '10

05 Sep '10

Hello, Sorry to ask another question so soon. I am trying to print out the =20 groundstate eigenvector to study entanglement by modifying the =20 sparsediag program. I put a simple For loop in the sparsediag.h file =20 as shown below, template <class T> void SparseDiagMatrix<T>::do_subspace() { typedef ietl::vectorspace<vector_type> vectorspace_type; boost::lagged_fibonacci607 generator; mag_vector_type ev; this->build(); if (this->dimension()=3D=3D0) return; vectorspace_type vec(this->dimension()); ietl::lanczos<matrix_type,vectorspace_type> lanczos(this->matrix(),vec); int n; if (this->dimension()>1) { int max_iter =3D =20 this->parms.value_or_default("MAX_ITERATIONS",std::min(int(10*this->dimensio= n()),1000)); int num_eigenvalues =3D =20 this->parms.value_or_default("NUMBER_EIGENVALUES",1); ietl::lanczos_iteration_nlowest<double> iter(max_iter,num_eigenvalues); std::cerr << "Starting Lanczos \n"; lanczos.calculate_eigenvalues(iter,generator); std::cerr << "Finished Lanczos\n"; n=3Dstd::min(num_eigenvalues,int(lanczos.eigenvalues().size())); ev.resize(n); for (int i=3D0;i<n;++i) ev[i]=3Dlanczos.eigenvalues()[i]; } else { ev.resize(1); ev[0]=3Dalps::real(value_type(this->matrix()(0,0))); } if (this->calc_averages()) { if (this->dimension()>1) { // calculate eigen vectors ietl::Info<magnitude_type> info; // (m1, m2, ma, eigenvalue, =20 residualm, status). try { eigenvectors.clear(); =20 lanczos.eigenvectors(lanczos.eigenvalues().begin(),lanczos.eigenvalues().beg= in()+n, std::back_inserter(eigenvectors),info,generato= r); =09=09 //code to print eigenvectors =09=09 for (int i=3D0;i<eigenvectors.size();++i) =09=09 { =09=09=09 std::cout << eigenvectors[i] << "\n"; =09=09 } } catch (std::runtime_error& e) { std::cout <<"Exception during eigenvector calculation: " << =20 e.what() << "\n"; } } =09 else { vector_type v(1); v[0]=3D1.; eigenvectors.push_back(v); } } this->perform_measurements(); eigenvectors.clear(); =20 std::copy(ev.begin(),ev.end(),std::back_inserter(this->measurements_.rbegin(= )->average_values["Energy"])); this->eigenvalues_.push_back(ev); } the following output is given for a 4 site spin 1/2 chain with J=3D1, Starting task 1. Quantumnumber Sz going from -2 to 2 with increment 1 Starting Lanczos Finished Lanczos [2]((-0.57735,0),(0.816497,0)) Starting Lanczos Finished Lanczos [2]((1.11022e-16,-8.65927e-17),(1,-4.98226e-17)) The problem is these numbers don't make sense at all, and when I try =20 to get the size of the eigenvector with eigenvector.size() it gives 1. =20 Any help or hints would be gratefully appreciated. Also any help or =20 hints about my other question about combining print_numeric and =20 sparsediag to get the ground state vector would be much appreciated. Thanks

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Averages vs MC time
by Giuseppe Carleo 04 Sep '10

04 Sep '10

Dear Alps developers, I would like to ask you a simple question about the simulation output of the alps scheduler: Is there a straightforward way to extract the average value of a given observable as a function of the monte carlo time? (for example, to roughly see wether the equilibration phase is completed). I couldn't find an example of this on the online tutorial. Thank you in advance, Giuseppe

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Fermion Hubbard Model
by João Manuel Viana Parente Lopes 03 Sep '10

03 Sep '10

Dear Alps users, First of all I want to congratulate you for the wonderful job of Alps. I was looking for information, to check if Alps is able to apply Quantum Monte Carlo to fermion Hubbard Model in half filling. If right now is not able do you think that this is an feature that we could expect from Alps in the future? Thanks in advance João Lopes

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Combining print_numeric and sparsediag to find Ground-State
by rexlundgren＠mail.utexas.edu 27 Aug '10

27 Aug '10

Hello all, I am trying to find the ground state eigenvector of a system to study entanglement. I read on a previous post that you can copy and paste the program print_numeric to the sparsediag program to print the basis vector of the ground state. I am however having some problems of knowing what to copy and paste due my inexperience with C++. I would be grateful for any help or hints on how to combine the two programs. Thanks, Rex

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worm algoritm
by Kubila 10 Aug '10

10 Aug '10

Hi At the moment I am testing a spin-1/2 model in a external magnetic field using worm algorithms. However it returns a error message " No subinterval found in traverse subintervals ". What exactly should I do in order to get the algorithm going? Thanks. Sincerely, Kubila

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Question on looper
by Klaus Larjo 10 Aug '10

10 Aug '10

Dear all, I'm studying the spin-1/2 XXZ spin chain. As I understand it, among other things the loop algorithm computes the partition function Z = Tr <n| e^(-bH) |n>, with b the inverse temperature, |n> a basis vector, and Tr a sum over that basis. However, I would like to compute matrix elements of the form <n| e^(-bH) |m>, where |n> and |m> are basis vectors to be specified by me. Is this possible to do via the looper algorithm, or any of the other ALPS algorithms based on worldline QMC? Thank you, Klaus

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[help] cannot compute local magnetization in ED
by jun wen 10 Aug '10

10 Aug '10

Hello All, I was trying to compute the local <S> in the Kitaev model defined on the honeycomb lattice with Exact Diagnolization Here is my parameter file: MODEL="kitaev"; LATTICE="honeycomb lattice"; LATTICE_LIBRARY="../../../definitions/kitaev/lattices.xml"; MODEL_LIBRARY="../../../definitions/kitaev/models.xml"; MEASURE_LOCAL[Local Sz]=Sz; MEASURE_LOCAL[Local Sx]=Sx; MEASURE_LOCAL[Local Sy]=Sy; local_S=1/2; L=2; W=2; J=1; However, in the output xml file, there are no such terms as the Local Sz or Local Splux or Local Sminus. I wonder if anyone could kindly point out what is the problem. The Kitaev model is defined in the following models.xml Thanks a lot! <MODELS> <SITEBASIS name="spin"> <PARAMETER name="local_spin" default="local_S"/> <PARAMETER name="local_S" default="1/2"/> <QUANTUMNUMBER name="S" min="local_spin" max="local_spin"/> <QUANTUMNUMBER name="Sz" min="-S" max="S"/> <OPERATOR name="Splus" matrixelement="sqrt(S*(S+1)-Sz*(Sz+1))"> <CHANGE quantumnumber="Sz" change="1"/> </OPERATOR> <OPERATOR name="Sminus" matrixelement="sqrt(S*(S+1)-Sz*(Sz-1))"> <CHANGE quantumnumber="Sz" change="-1"/> </OPERATOR> <OPERATOR name="Sz" matrixelement="Sz"/> </SITEBASIS> <SITEOPERATOR name="Sx" site="x"> 1/2*(Splus(x)+Sminus(x)) </SITEOPERATOR> <SITEOPERATOR name="Sy" site="x"> 1/2/I*(Splus(x)-Sminus(x)) </SITEOPERATOR> <BASIS name="spin"> <SITEBASIS ref="spin"/> </BASIS> <HAMILTONIAN name="kitaev"> <PARAMETER name="J1" default="1"/> <PARAMETER name="Jz" default="J1"/> <PARAMETER name="Jx" default="J1"/> <PARAMETER name="Jy" default="J1"/> <BASIS ref="spin"/> <BONDTERM type="0" source="i" target="j"> Jz*Sz(i)*Sz(j) </BONDTERM> <BONDTERM type="1" source="i" target="j"> Jx*Sx(i)*Sx(j) </BONDTERM> <BONDTERM type="2" source="i" target="j"> Jy*Sy(i)*Sy(j) </BONDTERM> </HAMILTONIAN> </MODELS> Jun

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calculation of local density of states
by Jun Wen 02 Aug '10

02 Aug '10

Dear all, Is it possible to calculate local density of states within the framework of exact diagonalization in ALPS? Thanks a lot! Best -- Jun Wen, Graduate Research Assistant Office: RLM 7.312 Department of Physics 1 University Station C1600 The University of Texas at Austin TX, 78712 Email: jwen(a)physics.utexas.edu junwen.ut(a)gmail.com

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Re: [ALPS-users] dmrg errors
by sebastian.greschner＠itp.uni-hannover.de 01 Aug '10

01 Aug '10

Hi Matthias, it seems to me that the segfaults occur for lattices with different types of vertices. For example, if I add fields at the beginning and the end of a Heisenberg-chain, I get segmentation faults for the following parameter file LATTICE_LIBRARY="mychain.xml" LATTICE="my open chain lattice N=16" MODEL="spin" NUMBER_EIGENVALUES=1 SWEEPS=4 COMPLEX=1 L=16 h0=1.5 h1=0.0 h2=1.5 MEASURE_LOCAL[Sz]=Sz {MAXSTATES=20} Strangely, if I change some parameters, for example set h0 and h2=1.0 or VERBOSE=1 everything works fine... Here mychain.xml just defines an open chain with edge-fields: <LATTICES> <GRAPH name = "my open chain lattice N=16" dimension="1" vertices="16" edges="15"> <VERTEX id="1" type="0"><COORDINATE>0</COORDINATE></VERTEX> <VERTEX id="2" type="1"><COORDINATE>1</COORDINATE></VERTEX> <VERTEX id="3" type="1"><COORDINATE>2</COORDINATE></VERTEX> <VERTEX id="4" type="1"><COORDINATE>3</COORDINATE></VERTEX> <VERTEX id="5" type="1"><COORDINATE>4</COORDINATE></VERTEX> <VERTEX id="6" type="1"><COORDINATE>5</COORDINATE></VERTEX> <VERTEX id="7" type="1"><COORDINATE>6</COORDINATE></VERTEX> <VERTEX id="8" type="1"><COORDINATE>7</COORDINATE></VERTEX> <VERTEX id="9" type="1"><COORDINATE>8</COORDINATE></VERTEX> <VERTEX id="10" type="1"><COORDINATE>9</COORDINATE></VERTEX> <VERTEX id="11" type="1"><COORDINATE>10</COORDINATE></VERTEX> <VERTEX id="12" type="1"><COORDINATE>11</COORDINATE></VERTEX> <VERTEX id="13" type="1"><COORDINATE>12</COORDINATE></VERTEX> <VERTEX id="14" type="1"><COORDINATE>13</COORDINATE></VERTEX> <VERTEX id="15" type="1"><COORDINATE>14</COORDINATE></VERTEX> <VERTEX id="16" type="2"><COORDINATE>15</COORDINATE></VERTEX> <EDGE source="1" target="2" id="1" type="0" vector="1"/> <EDGE source="2" target="3" id="2" type="0" vector="1"/> <EDGE source="3" target="4" id="3" type="0" vector="1"/> <EDGE source="4" target="5" id="4" type="0" vector="1"/> <EDGE source="5" target="6" id="5" type="0" vector="1"/> <EDGE source="6" target="7" id="6" type="0" vector="1"/> <EDGE source="7" target="8" id="7" type="0" vector="1"/> <EDGE source="8" target="9" id="8" type="0" vector="1"/> <EDGE source="9" target="10" id="9" type="0" vector="1"/> <EDGE source="10" target="11" id="10" type="0" vector="1"/> <EDGE source="11" target="12" id="11" type="0" vector="1"/> <EDGE source="12" target="13" id="12" type="0" vector="1"/> <EDGE source="13" target="14" id="13" type="0" vector="1"/> <EDGE source="14" target="15" id="14" type="0" vector="1"/> <EDGE source="15" target="16" id="15" type="0" vector="1"/> </GRAPH> </LATTICES> Can you reproduce this error?! Sebastian On 23/07/10 15:23, Matthias Troyer wrote: > Hi Sebastian, > > can you please post an example parameter file that segfaults at the > beginning? > > Matthias > > On 23 Jul 2010, at 03:53, Sebastian Greschner wrote: > >> Hi Matthias, >> >> Thank you - now dmrg gives the correct results! >> >> Unfortunately there is still one (but probably unrelated) problem with >> dmrg (I am working on a Debian Lenny system - Intel Xeon): Depending on >> the parameters I choose (some special model parameters, Number of >> MAXSTATES, etc.) in the parameter file, I sometimes get segmentation >> faults at the beginning or at the end. Sorry - I haven't figured out >> yet, when this happens exactly, but maybe somebody has observed similar >> errors... >> >> Best, >> Sebastian >> >> On 22/07/10 17:25, Matthias Troyer wrote: >>> >>> On 22 Jul 2010, at 05:33, Sebastian Greschner wrote: >>> >>>> Hi, >>>> >>>> I am having some trouble with the dmrg-program (e.g. of current ALPS >>>> 2.0b3) and "complex-valued" models. >>>> It seems to me that dmrg ignores the imaginary part of model-parameters >>>> (even with COMPLEX set to true). "sparsediag" gives the correct results. >>>> >>>> Is this a bug or a general restriction of the dmrg-program? Or is it >>>> just a problem of my model or my local installation? >>>> >>>> Thanks in advance and greetings, >>>> Sebastian >>>> >>> >>> >>> Hi Sebastian, >>> >>> I fixed one bug and the fix will show up in the MacOS and source >>> versions of thennext nightly snapshot (Friday morning). Can you >>> please try that? >>> >>> Matthias >>> >>> >> > >

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generalized susceptibility in loop algorithm
by Kubila 28 Jul '10

28 Jul '10

Hi all Currently I am studying spin-1/2 XY model using the loop algorithm in ALPS. The staggered susceptibility measured using the loop algorithm does not grow with space-time volume. On the other hand, the generalized susceptibility measured using the loop algorithm seems to scale with space-time volume. I was wondering is the generalized susceptibility exactly the correlator of the X-component of the staggered magnetization M_s = \sum_{x} (-1)^{x_1+x_2}\vec{S}_x?, here \vec{S}_x is the spin-1/2 operator at site x. Also is the z-direction the quantized direction in the loop algorithm? Thanks in advance. kubila

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