Now showing items 756-774 of 774

    • Variationally Constrained Numerical Solution of Electrical Impedance Tomography 

      Borcea, Liliana; Gray, Genetha Anne; Zhang, Yin (2002-10)
      We propose a novel, variational inversion methodology for the electrical impedance tomography problem, where we seek electrical conductivity σ inside a bounded, simply connected domain Ω, given simultaneous measurements ...
    • Variations of Structured Broyden Families for Nonlinear Least Squares Problems 

      Yabe, H. (1992-06)
      In this paper, we consider structured quasi-Newton methods for finding a local solution to nonlinear least squares problems. This paper is concerned with the line search globalization method. Recently, factorized versions ...
    • Velocity Analysis in the Presence of Uncertainty 

      Dussaud, Eric Albert (2006-06)
      Velocity analysis resolves relatively long scales of earth structure, on the order of 1 km. Migration produces images with length scales (wavelengths) on the order of 10's of m. In between these two scale regimes lies ...
    • Velocity Inversion by Coherency Optimization 

      Symes, William W.; Carazzone, J.J. (1989-08)
      We introduce an approach to velocity and reflectivity estimation based on optimizing the coherence of multiple shot-gather inversions of reflection seismograms. The resulting algorithm appears to avoid the severe convergence ...
    • Velocity Inversion by Coherency Optimization 

      Symes, William W. (1988-04)
      We introduce an approach to velocity and reflectivity estimation based on optimizing the coherence of multiple shot-gather inversions of reflection seismograms. The resulting algorithm appears to avoid the severe convergence ...
    • Velocity Inversion by Differential Semblance Optimization for 2D Common Source Data 

      Symes, William W.; Kern, Michel (1992-04)
      Differential Semblance Optimization ("DSO") is a variant of data-fitting (least-squares) inversion of reflection seismograms. The misfit functions used in other implementations of least-squares inversion (for example ...
    • Velocity Inversion: A Case Study in Infinite-Dimensional Optimization 

      Symes, William W. (1988-07)
      The goal of seismic velocity inversion is the estimation of seismic wave velocities inside the earth by attempting to predict, in a least-error sense, seismic waveforms measured at its surface. We present velocity inversion ...
    • Verifying A Runge-Kutta Solver Using ADOL-C 

      Edwards, Chantal; Fagan, Mike (2003-11)
      This report describes our effort to verify differential equation solvers using automatic differentiation (AD). In particular, the report describes the AD verification technique in general, as well as the application of the ...
    • Very Large-Scale Linear Programming: A Case Study in Combining Interior Point and Simplex Methods 

      Bixby, Robert E.; Gregory, John W.; Lustig, Irvin J.; Marsten, Roy E.; Shanno, David F. (1991-05)
      Experience with solving a 12,753,313 variable linear program is described. This problem is the linear programming relaxation of a set partitioning problem arising from an airline crew scheduling application. A scheme is ...
    • Viscoelastic Finite Difference Modeling 

      Blanch, Joakim O.; Robertsson, Johan O.A.; Symes, William W. (1993-02)
      Real earth media disperse and attenuate propagating waves. This anelastic behavior can be well described by a viscoelastic model. We have developed a finite difference simulator to model wave propagation in viscoelastic ...
    • Viscoelastic Finite Difference Modeling II 

      Blanch, Joakim O.; Robertsson, Johan O.A.; Symes, William W. (1993-05)
      Real earth media disperse and attenuate propagating mechanical waves. This anelastic behavior can be described well by a viscoelastic model. We have developed a finite difference simulator to model wave propagation in ...
    • Wavefield Splitting and Extrapolation of the Two Dimensional Plasma Wave Equation 

      Song, H.; Zhang, G. (1992-08)
      Wave splitting is an important technique in a great variety of studies concerning wave propagation. It is a class of methods of splitting the wave equation under consideration into one way wave equations, or physically ...
    • Weighted Least Squares Estimators on the Frequency Domain for the Parameters of a Time Series 

      Chiu, Shean-Tsong (1986-09)
      A procedure for estimating the parameters of a time series is proposed. The estimate minimizes a criterion function which is the weighted sum of squares of the distances between the periodograms and the spectrum of the ...
    • Weighting Schemes and Objective Functions in Sub-Surface Flow and Transport Parameter Identification via Inverse Simulation 

      Carey, Martha M. (1995-10)
      We propose a number of different weighting schemes (piecewise linear, quadratic, sine and narrow-base sine) based on data magnitude for least-squares minimization of concentration data for parameter estimation for groundwater ...
    • Well-posedness of Initial/Boundary Value Problems for Hyperbolic Integro-differential Systems with Nonsmooth Coefficients 

      Blazek, Kirk D.; Stolk, Christiaan; Symes, William W. (2008-10)
      In the late 1960's, J.-L. Lions and collaborators showed that energy estimates could be used to establish existence, uniqueness, and continuous dependence on initial data for finite energy solutions of initial/boundary ...
    • What Happens When We Trust a Region That is a Line? 

      Vicente, Luís N. (1995-04)
      Line searches and trust regions are two techniques to globalize nonlinear optimization algorithms. We claim that the trust-region technique has built-in an appropriate regularization of ill-conditioned second-order ...
    • What is Simulated Annealing? 

      Trosset, Michael W. (2000-02)
      Beginning in 1983, simulated annealing was marketed as a global optimization methodology that mimics the physical annealing process by which molten substances cool to crystalline lattices of minimal energy. This marketing ...
    • When is Missing Data Recoverable? 

      Zhang, Yin (2006-10)
      Suppose a non-random portion of a data vector is missing. With some minimal prior knowledge about the data vector, can we recover the missing portion from the available one? In this paper, we consider a linear programming ...
    • ønix: A Unix Emulator for VAX/VMS 

      Caplinger, Michael (1987-08)