Angelos T. Vouldis

Globally flexible functional forms: The neural distance function ☆

The output distance function is a key concept in economics. However, its empirical estimation often violates properties dictated by neoclassical production theory. In this paper, we introduce the neural distance function (NDF) which constitutes a global approximation to any arbitrary production technology with multiple outputs given by a neural network (NN) specification. The NDF imposes all theoretical properties such as monotonicity, curvature and homogeneity, for all economically admissible values of outputs and inputs. Fitted to a large data set for all US commercial banks (1989-2000), the NDF explains a very high proportion of the variance of output while keeping the number of parameters to a minimum and satisfying the relevant theoretical properties. All measures such as total factor productivity (TFP) and technical efficiency (TE) are computed routinely. Next, the NDF is compared with the Translog popular specification and is found to provide very satisfactory results as it possesses the properties thought as desirable in neoclassical production theory in a way not matched by its competing specification.

Three-Dimensional Diffraction Tomography Using Filtered Backpropagation and Multiple Illumination Planes

In this paper, a three-dimensional (3-D) extension of the well-known filtered-backpropagation (FBP) algorithm is presented with the aim of taking into account scattered-field-data measurements obtained using incident directions not restricted in a single plane. The FBP algorithm has been extensively used to solve the two-dimensional inverse-scattering problem under the first-order Born and Rytov approximations for weak scatterers. The extension of this algorithm in three dimensions is not straightforward, because the task of collecting the data needed to obtain a low-pass filtered version of the scattering object, taking into account all spatial frequencies within a radius of radic2k0, and of incorporating these data to the FBP algorithm, needs to be addressed. A simple extension using incident field directions restricted to a single plane (illumination plane) leaves a region of spatial frequencies of the sphere of radius radic2k 0 undetermined. The locus of these spatial frequencies may be crucial for the accurate reconstruction of objects which do not vary slowly along the axis perpendicular to the illumination plane. The proposed 3-D FBP algorithm presented here is able to incorporate the data collected from more than one illumination plane and to ensure the reliability of the reconstruction results

Emil Lederer and the Schumpeter–Hilferding–Tugan-Baranowsky Nexus

This paper focuses on the thinking of Emil Lederer, one of the leading academic socialists of Germany in the 1920s. Lederers views on economic development, technical change, credit and business cycles are compared to those of Schumpeter. The paper traces the roots of some of their ideas back to the work of two prominent Marxists, Rudolf Hilferding and Mikhail Ivanovich Tugan-Baranowsky. The paper concludes that although Lederer and Schumpeter are traditionally classified in different schools of thought, their theoretical views on many issues converge.

Heterodox influences on Schumpeter

Purpose - Joseph Alois Schumpeters ideas are in the discussion agenda of various economists working in different theoretical traditions. However, several aspects of his work remain unexplored. In particular, the origin of his ideas in the context of the then prevalent economic theories of the German-speaking camp, have not been widely discussed. The purpose of this paper is claim that the elaborations of certain German-speaking heterodox economists and/or schools of economic thought may be traced in Schumpeters Design/methodology/approach - The influence of the German Historical School and specifically of Gustav von Schmoller, Max Weber and Werner Sombart on typical Schumpeterian themes is examined. In a similar vein, it is argued that Schumpeters analysis presents striking similarities with the works of the Austro-Marxist Economist Rudolf-Hilferding and the Austrian Social Democrat Emil Lederer. Findings - In this context, certain Schumpeterian insights appear less original. Originality/value - Conclusively, it may be inferred that a deeper understanding of Schumpeterian economic analysis presupposes an acquaintance with certain heterodox theoretical traditions of the German-speaking world.

Emil Lederer and Joseph Schumpeter on Economic Growth, Technology and Business Cycles

This paper compares Joseph Schumpeter and Emil Lederer with respect to their visions concerning the notions of economic growth, technology and business cycles. Their theoretical investigations in a number of thematic areas seem to converge to similar views. More precisely, both Schumpeter and Lederer regard the capitalist economy as a dynamic system where the introduction of innovations is its distinctive characteristic. In such a system, static analysis based on the concept of equilibrium is useful as an expository device to describe the adjustment mechanisms of the economic system. They also paid attention to the emergence of large oligopolistic firms and considered this development as being interwoven with technological progress. Both economists used similar arguments to emphasize the link between economic development and technological change. In their analyses, Schumpeter and Lederer referred to psychological factors motivating the entrepreneur, in order to explain the forces that set in motion the process of innovation and thus economic development. The concept of technological unemployment is also described in a similar manner by both of them. Regarding the issue of business cycles, Schumpeter and Lederer considered them to be a result of endogenous processes within a capitalist economy. Lederer in his late works, argued in a way analogous to Schumpeter, that economic fluctuations are caused from the disruptions created by innovations, which are introduced discontinuously into the economic system. Conclusively, Schumpeter and Lederer delivered theses which are similar in scope and conclusions probably because they were developed in the same social, political, theoretical and ideological environment and were also well acquainted with each other’s ideas.

Global Approximations to Cost and Production Functions using Artificial Neural Networks

The estimation of cost and production functions in economics usually relies on standard specifications which are less that satisfactory in numerous situations. However, instead of fitting the data with a pre-specified model, Artificial Neural Networks (ANNs) let the data itself serve as evidence to support the models estimation of the underlying process. In this context, the proposed approach combines the strengths of economics, statistics and machine learning research and the paper proposes a global approximation to arbitrary cost and production functions, respectively, given by ANNs. Suggestions on implementation are proposed. All relevant measures such as Returns to Scale (RTS) and Total Factor Productivity (TFP) may be computed routinely.

Efficient Preconditioning of the Method of Auxiliary Sources (MAS) for Cylindrical Scatterers of Quasi- Circular Cross-Section

Two different forms of a preconditioning process (i.e. standard preconditioning and quasi-diagonalization) are presented, in conjunction with the Method of Auxiliary Sources (MAS), when the latter is applied to a specific class of two-dimensional scattering problems. The method enhances the efficiency of MAS, when the linear system becomes ill- conditioned, due to distancing of the auxiliary surface from the outer boundary. If the cross-sectional boundary is geomet- rically close to a circle, it is proven that the MAS matrix becomes quasi-circulant, as intuition dictates. By exploiting the properties of the exactly circulant matrix, pertaining to the original circular configuration, the perturbed system is trans- formed to a quasi-diagonal one, whose inversion is a numerically stable operation.

Preconditioning techniques for the method of auxiliary sources applied to geometries characterized as perturbations of a circle

Two versions of a preconditioning procedure are described for a class of two-dimensional scattering problems, when the latter are solved via the Method of Auxiliary Sources (MAS). The method is useful for the case of shrinking auxiliary surfaces, i.e. when the linear system may become ill-conditioned. If the cross sectional boundary can be regarded as a deformation of a circle, the MAS matrix is shown to be quasi-circulant, as expected intuitively. By utilizing the circulant properties of the matrix pertaining to the original circular configuration, the perturbed system is transformed to a quasi-diagonal one, whose inversion is a numerically stable operation.

On the data needed for the accurate reconstruction in 3D diffraction tomography

In this paper, the three dimensional (3D) extensions of the two well-known diffraction tomography algorithms, namely direct Fourier interpolation and filtered backpropagation (FBP) are presented. These algorithms solve the linearized version of the inverse scattering problem using either the Born or the Rytov approximations which are known to be valid for weak scatterers. We investigate the problem of the amount of data needed for a full 3D reconstruction. Previous attempts for 3D reconstruction using several inverse scattering algorithms were based on scattered field measurements with incident pulse directions restricted exclusively on the xy-plane. This results in ignoring the contribution of some spatial frequencies which are near the z-axis. This effect is studied here by comparing the results of reconstruction with and without data obtained from other incident directions which fill the spatial frequency domain. We conclude that for a class of objects presenting smooth variation along the z-axis, the use of data obtained for incident direction only in the xy-plane is sufficient to obtain a satisfactory quality of reconstruction while quick variations along the z-axis cannot be imagined.

Emil Lederer’s Theory of Economic Fluctuations and the Role of Financial Institutions

Emil Lederer was characterized as the “leading academic socialist of Germany in the 1920’s” by Joseph Schumpeter and was a highly respected economist of his time. However, most aspects of his work remain totally unexplored. This paper focuses on Emil Lederer’s theory of economic fluctuations defending the thesis that certain aspects of Lederer’s conceptualization of economic fluctuations underwent considerable modifications when his 1925 article Konjunktur und Krisen is compared with his 1938 book Technical Progress and Unemployment., a shift unacknowledged so far in the literature. In his first attempt to tackle the issue, in Konjunktur und Krisen (1925), Lederer had constructed an explanation consistent with the so-called “disproportionality theory” introduced by Tugan-Baranowsky (codified as “early Lederer”). However, Lederer’s conception of the business cycle during the 1930s and especially in his major work Technical Progress and Unemployment underwent considerable modifications. Lederer’s (1938) analysis is, apparently, very ‘Schumpeterian’ (codified as “late Lederer”). In this version of his theory, the cycle is explained by supply-side factors, and more specifically by technical change. Additionally, Lederer’s view on the role of financial institutions (credit and banks) with regards to business cycles is analysed. Lederer avoided attributing a causative role to monetary factors. The interrelation between ‘real’ factors and financial institutions constitutes an essential element in his analysis of the business cycle.