57,973 research outputs found
Modified repeated median filters
We discuss moving window techniques for fast extraction of a signal comprising monotonic trends and abrupt shifts from a noisy time series with irrelevant spikes. Running medians remove spikes and preserve shifts, but they deteriorate in trend periods. Modified trimmed mean filters use a robust scale estimate such as the median absolute deviation about the median (MAD) to select an adaptive amount of trimming. Application of robust regression, particularly of the repeated median, has been suggested for improving upon the median in trend periods. We combine these ideas and construct modified filters based on the repeated median offering better shift preservation. All these filters are compared w.r.t. fundamental analytical properties and in basic data situations. An algorithm for the update of the MAD running in time O(log n) for window width n is presented as well. --signal extraction,robust filtering,drifts,jumps,outliers,computational geometry,update algorithm
Modified Repeated Median Filters
We discuss moving window techniques for fast extraction of a signal comprising monotonic trends and abrupt shifts from a noisy time series with irrelevant spikes. Running medians remove spikes and preserve shifts, but they deteriorate in trend periods. Modified trimmed mean filters use a robust scale estimate such as the median absolute deviation about the median (MAD) to select an adaptive amount of trimming. Application of robust regression, particularly of the repeated median, has been suggested for improving upon the median in trend periods. We combine these ideas and construct modified filters based on the repeated median offering better shift preservation. All these filters are compared w.r.t. fundamental analytical properties and in basic data situations. An algorithm for the update of the MAD running in time O(log n) for window width n is presented as well
Multi Stage based Time Series Analysis of User Activity on Touch Sensitive Surfaces in Highly Noise Susceptible Environments
This article proposes a multistage framework for time series analysis of user
activity on touch sensitive surfaces in noisy environments. Here multiple
methods are put together in multi stage framework; including moving average,
moving median, linear regression, kernel density estimation, partial
differential equations and Kalman filter. The proposed three stage filter
consisting of partial differential equation based denoising, Kalman filter and
moving average method provides ~25% better noise reduction than other methods
according to Mean Squared Error (MSE) criterion in highly noise susceptible
environments. Apart from synthetic data, we also obtained real world data like
hand writing, finger/stylus drags etc. on touch screens in the presence of high
noise such as unauthorized charger noise or display noise and validated our
algorithms. Furthermore, the proposed algorithm performs qualitatively better
than the existing solutions for touch panels of the high end hand held devices
available in the consumer electronics market qualitatively.Comment: 9 pages (including 9 figures and 3 tables); International Journal of
Computer Applications (published
Robust Filters for Intensive Care Monitoring: Beyond the Running Median
Current alarm systems on intensive care units create a very high rate of false positive alarms because most of them simply compare the physiological measurements to fixed thresholds. An improvement can be expected when the actual measurements are replaced by smoothed estimates of the underlying signal. However, classical filtering procedures are not appropriate for signal extraction as standard assumptions, like stationarity, do no hold here: the measured time series often show long periods without change, but also upward or downward trends, sudden shifts and numerous large measurement artefacts. Alternative approaches are needed to extract the relevant information from the data, i.e. the underlying signal of the monitored variables and the relevant patterns of change, like abrupt shifts and trends. This article reviews recent research on filter based online signal extraction methods which are designed for application in intensive care. --
Deep neural networks for direct, featureless learning through observation: the case of 2d spin models
We demonstrate the capability of a convolutional deep neural network in
predicting the nearest-neighbor energy of the 4x4 Ising model. Using its
success at this task, we motivate the study of the larger 8x8 Ising model,
showing that the deep neural network can learn the nearest-neighbor Ising
Hamiltonian after only seeing a vanishingly small fraction of configuration
space. Additionally, we show that the neural network has learned both the
energy and magnetization operators with sufficient accuracy to replicate the
low-temperature Ising phase transition. We then demonstrate the ability of the
neural network to learn other spin models, teaching the convolutional deep
neural network to accurately predict the long-range interaction of a screened
Coulomb Hamiltonian, a sinusoidally attenuated screened Coulomb Hamiltonian,
and a modified Potts model Hamiltonian. In the case of the long-range
interaction, we demonstrate the ability of the neural network to recover the
phase transition with equivalent accuracy to the numerically exact method.
Furthermore, in the case of the long-range interaction, the benefits of the
neural network become apparent; it is able to make predictions with a high
degree of accuracy, and do so 1600 times faster than a CUDA-optimized exact
calculation. Additionally, we demonstrate how the neural network succeeds at
these tasks by looking at the weights learned in a simplified demonstration
Comparison of Algorithms for Baseline Correction of LIBS Spectra for Quantifying Total Carbon in Brazilian Soils
LIBS is a promising and versatile technique for multi-element analysis that
usually takes less than a minute and requires minimal sample preparation and no
reagents. Despite the recent advances in elemental quantification, the LIBS
still faces issues regarding the baseline produced by background radiation,
which adds non-linear interference to the emission lines. In order to create a
calibration model to quantify elements using LIBS spectra, the baseline has to
be properly corrected. In this paper, we compared the performance of three
filters to remove random noise and five methods to correct the baseline of LIBS
spectra for the quantification of total carbon in soil samples. All
combinations of filters and methods were tested, and their parameters were
optimized to result in the best correlation between the corrected spectra and
the carbon content in a training sample set. Then all combinations with the
optimized parameters were compared with a separate test sample set. A
combination of Savitzky-Golay filter and 4S Peak Filling method resulted in the
best correction: Pearson's correlation coefficient of 0.93 with root mean
square error of 0.21. The result was better than using a linear regression
model with the carbon emission line 193.04 nm (correlation of 0.91 with error
of 0.26). The procedure proposed here opens a new possibility to correct the
baseline of LIBS spectra and to create multivariate methods based on the a
given spectral range.Comment: 13 pages, 5 figure
Selection from read-only memory with limited workspace
Given an unordered array of elements drawn from a totally ordered set and
an integer in the range from to , in the classic selection problem
the task is to find the -th smallest element in the array. We study the
complexity of this problem in the space-restricted random-access model: The
input array is stored on read-only memory, and the algorithm has access to a
limited amount of workspace. We prove that the linear-time prune-and-search
algorithm---presented in most textbooks on algorithms---can be modified to use
bits instead of words of extra space. Prior to our
work, the best known algorithm by Frederickson could perform the task with
bits of extra space in time. Our result separates
the space-restricted random-access model and the multi-pass streaming model,
since we can surpass the lower bound known for the latter
model. We also generalize our algorithm for the case when the size of the
workspace is bits, where . The running time
of our generalized algorithm is ,
slightly improving over the
bound of Frederickson's algorithm. To obtain the improvements mentioned above,
we developed a new data structure, called the wavelet stack, that we use for
repeated pruning. We expect the wavelet stack to be a useful tool in other
applications as well.Comment: 16 pages, 1 figure, Preliminary version appeared in COCOON-201
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