Where are we now? A large benchmark study of recent symbolic regression methods

In this paper we provide a broad benchmarking of recent genetic programming approaches to symbolic regression in the context of state of the art machine learning approaches. We use a set of nearly 100 regression benchmark problems culled from open source repositories across the web. We conduct a rigorous benchmarking of four recent symbolic regression approaches as well as nine machine learning approaches from scikit-learn. The results suggest that symbolic regression performs strongly compared to state-of-the-art gradient boosting algorithms, although in terms of running times is among the slowest of the available methodologies. We discuss the results in detail and point to future research directions that may allow symbolic regression to gain wider adoption in the machine learning community.Comment: 8 pages, 4 figures. GECCO 201

A plasticity model for powder compaction processes incorporating particle deformation and rearrangement

This article is available open access through the publisher’s website at the link below. Copyright @ 2008 Elsevier Ltd.This paper develops a mechanistic model of granular materials that can be used with a commercial finite element package (ABAQUS). The model draws on the ideas of critical state soil mechanics and combines them with the theory of envelopes to develop an elasto-plastic model with a non-associated flow rule. The model incorporates both local deformation at the granule contacts, and rearrangement of the granules so that jointly they account for any bulk deformation. The mechanics of the model closely reflect the physicality of the material behaviour and the model parameters are closely linked (although not simplistically identical) to the characteristics of the granules. This not only gives an insight into the material behaviour, but also enables the model to be used to facilitate design of the material, its processing properties and, hence, component development. The model is used to simulate drained triaxial tests, settlement of a powder in a bin, and some examples of die pressing. Simulations are compared with experimental data and with predictions obtained using other models

Relationship Banking and Loan Syndicate Structure: The Role of Private Equity Sponsors

Using a sample of syndicated loans to private equity (PE)-backed IPO companies, we examine how a third-party bank relationship influences the syndicate structure of a loan. We find that a stronger relationship between the lead bank and the borrower’s PE firm enables the lead bank to retain a smaller share of the loan and form a larger and less concentrated syndicate, especially when the borrower is less transparent. A stronger PE-bank relationship also attracts greater foreign bank participation. Our findings suggest that the lead bank’s relationship with a large equity holder of the borrower facilitates information production in lending

The rotational excitation of HCN and HNC by He: New insights on the HCN/HNC abundance ratio in molecular clouds

Modeling of molecular emission from interstellar clouds requires the calculation of rates for excitation by collisions with the most abundant species. The present paper focuses on the calculation of rate coefficients for rotational excitation of the HCN and HNC molecules in their ground vibrational state in collision with He. The calculations are based on new two-dimensional potential energy surfaces obtained from highly correlated \textit{ab initio} calculations. Calculations of pure rotational (de)excitation cross sections of HCN and HNC by He were performed using the essentially exact close-coupling method. Cross sections for transitions among the 8 first rotational levels of HCN and HNC were calculated for kinetic energies up to 1000 cm$^{-1}$. These cross sections were used to determine collisional rate constants for temperatures ranging from 5 K to 100 K. A propensity for even $\Delta j$ transitions is observed in the case of HCN--He collisions whereas a propensity for odd $\Delta j$ transitions is observed in the case of HNC--He collisions. The consequences for astrophysical models are evaluated and it is shown that the use of HCN rate coefficients to interpret HNC observations can lead to significant inaccuracies in the determination of the HNC abundance, in particular in cold dark clouds for which the new HNC rates show that the $j=1-0$ line of this species will be more easily excited by collisions than HCN. An important result of the new HNC-He rates is that the HNC/HCN abundance ratio derived from observations in cold clouds has to be revised from $>$1 to $\simeq$1, in good agreement with detailed chemical models available in the literature.Comment: 8 figue

New Measurements of Nucleon Structure Functions from the CCFR/NuTeV Collaboration

We report on the extraction of the structure functions F_2 and Delta xF_3 = xF_3nu-xF_3nubar from CCFR neutrino-Fe and antineutrino-Fe differential cross sections. The extraction is performed in a physics model independent (PMI) way. This first measurement for Delta xF_3, which is useful in testing models of heavy charm production, is higher than current theoretical predictions. The F_2 (PMI) values measured in neutrino and muon scattering are in good agreement with the predictions of Next to Leading Order PDFs (using massive charm production schemes), thus resolving the long-standing discrepancy between the two sets of data.Comment: 5 pages. Presented by Arie Bodek at the CIPNAP2000 Conference, Quebec City, May 200