Reconfigurable computing for Monte Carlo simulations: results and prospects of the Janus project

We describe Janus, a massively parallel FPGA-based computer optimized for the simulation of spin glasses, theoretical models for the behavior of glassy materials. FPGAs (as compared to GPUs or many-core processors) provide a complementary approach to massively parallel computing. In particular, our model problem is formulated in terms of binary variables, and floating-point operations can be (almost) completely avoided. The FPGA architecture allows us to run many independent threads with almost no latencies in memory access, thus updating up to 1024 spins per cycle. We describe Janus in detail and we summarize the physics results obtained in four years of operation of this machine; we discuss two types of physics applications: long simulations on very large systems (which try to mimic and provide understanding about the experimental non equilibrium dynamics), and low-temperature equilibrium simulations using an artificial parallel tempering dynamics. The time scale of our non-equilibrium simulations spans eleven orders of magnitude (from picoseconds to a tenth of a second). On the other hand, our equilibrium simulations are unprecedented both because of the low temperatures reached and for the large systems that we have brought to equilibrium. A finite-time scaling ansatz emerges from the detailed comparison of the two sets of simulations. Janus has made it possible to perform spin glass simulations that would take several decades on more conventional architectures. The paper ends with an assessment of the potential of possible future versions of the Janus architecture, based on state-of-the-art technology.

Tethered Monte Carlo: computing the effective potential without critical slowing down

We present Tethered Monte Carlo, a simple, general purpose method of computing the effective potential of the order parameter (Helmholtz free energy). This formalism is based on a new statistical ensemble, closely related to the micromagnetic one, but with an extended configuration space (through Creutz-like demons). Canonical averages for arbitrary values of the external magnetic field are computed without additional simulations. The method is put to work in the two-dimensional Ising model, where the existence of exact results enables us to perform high precision checks. A rather peculiar feature of our implementation, which employs a local Metropolis algorithm, is the total absence, within errors, of critical slowing down for magnetic observables. Indeed, high accuracy results are presented for lattices as large as L = 1024.

Mean-value identities as an opportunity for Monte Carlo error reduction

In the Monte Carlo simulation of both lattice field theories and of models of statistical mechanics, identities verified by exact mean values, such as Schwinger-Dyson equations, Guerra relations, Callen identities, etc., provide well-known and sensitive tests of thermalization bias as well as checks of pseudo-random-number generators. We point out that they can be further exploited as control variates to reduce statistical errors. The strategy is general, very simple, and almost costless in CPU time. The method is demonstrated in the twodimensional Ising model at criticality, where the CPU gain factor lies between 2 and 4.

Tethered Monte Carlo: computing the effective potential without critical slowing down

We present Tethered Monte Carlo, a simple, general purpose method of computing the effective potential of the order parameter (Helmholtz free energy). This formalism is based on a new statistical ensemble, closely related to the micromagnetic one, but with an extended configuration space (through Creutz-like demons). Canonical averages for arbitrary values of the external magnetic field are computed without additional simulations. The method is put to work in the two-dimensional Ising model, where the existence of exact results enables us to perform high precision checks. A rather peculiar feature of our implementation, which employs a local Metropolis algorithm, is the total absence, within errors, of critical slowing down for magnetic observables. Indeed, high accuracy results are presented for lattices as large as L = 1024.

Optimized Monte Carlo method for glasses

A new Monte Carlo algorithm is introduced for the simulation of supercooled liquids and glass formers, and tested in two model glasses. The algorithm thermalizes well below the Mode Coupling temperature and outperforms other optimized Monte Carlo methods.

Commonplace book of John Bullard, 1775-1779

This bound volume contains excerpts copied by Jonathan Bullard from books he read as a student at Harvard in the mid 1770s. Excerpts include an unattributed poem titled "On Friendship," which appeared in the "poetical essays" section of Volume 36 of the London Magazine in 1767; Joseph Butler, The Analogy of Religion, 1736; The Quaker's Grace; a history of England; Newton's laws; Plutarch's Morals; Benjamin Franklin's writings on the Aurora Borealis. The volume also includes several extracts from articles about the death of John Paddock (Class of 1776), who drowned in the Charles in the summer of 1773, sheet music for two songs, "The Rapture," and "A Song" from Henry Harington's "Damon and Chlora," and a transcription of the satirical "Book of Harvard," written in response to the Butter Rebellion of 1766. Interleaved in the middle of the volume is a transcription from an ecclesiastical event moderated by Ebenezer Bridge in Medford, Mass. on November 20, 1779. The variety of texts suggests the commonplace book was not used solely for academic works.

Binding papers, 1775-1928

The binding papers contain lists of volumes bound for the Harvard library in the form of lists and bills. The books are generally identified by title, volume size (octavo, quarto, folio, etc.), or both. The series includes two 18th century documents. The first document is a one-page January 22, 1775 bill to Harvard College from "Dr. And'r Barclay" for the binding and numbering of books. Books are identified by volume size. The second document is a one-page "List of books belonging to the Library which it is necessary should be new-bound" with an initial list signed by James Winthrop the Librarian on December 13, 1786, an additional list made on April 7, 1787, and subsequent notes made in May 1787. The books are indicated by title and size.

Per Carlo Maria Maggi : inaugurandosi il monumento alle Scuole Palatine, nel IIo centenario della morte, 1630-1699 /

Copy 2: University of Illinois bookplate: "From the library of Conte Antonio Cavagna Sangiuliani di Gualdana Lazelada di Bereguardo, purchased 1921".

Testamento del fu Carlo Archinto Visconti Panigarola del giorno 22 maggio 1804 e successiva carta addizionale, 31 detto mese.

University of Illinois bookplate: "From the library of Conte Antonio Cavagna Sangiuliani di Gualdana Lazelada di Bereguardo, purchased 1921."

Historia parlamentaria de los Congresos Mexicanos de 1821 a 1857 /

Facsimile of 1877 edition.

Historia de las insurrecciones de Tacna por la independencia del Perú; 1810-1811-1813-1815-1818-1821.

Mode of access: Internet.

[La Fisonomia dell'huomo, et la Celeste di Gio. Battista dalla Porta, libri sei tradotti di latino in volgare ...]

La tercera parte contiene: 1. Fisonomía di Polemone tradotta di greco in latino del Carlo Montecuccoli, con annotatione del medesmo, et poscia di latino fatta volgare dal conte Francesco suo fratello -- 2. Fisonomia natvrale di Monsignore Giovanni Ingegneri.

Censura sobre el arte de pensar o Logica admirable de don Antonio Arnaldo ... /

Mode of access: Internet.

Esame e difesa del decreto pubblicato in Pudisceri da monsignor Carlo Tommaso di Tournon ... approvato e confermato con breve dal sommo pontefice Benedetto XIII /

Mode of access: Internet.

Sucinta relación de las principales operaciones del Escmo. Ayuntamiento Constitucional de la ciudad de Barcelona en el año 1821

Mode of access: Internet.