# Tagged Questions

Questions on the use of mathematical techniques to extract properties from given data. Consider if your question might be more suited for Cross Validated (stats.SE) instead.

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### How to visualize change over time of multiple items at once?

I'm writing a recommendation system for a news website. At any point in time, there are between 50-100 articles that are candidates for recommendation based on the algorithm, etc. What I'm trying to ...
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### How to find an equation that describes a non-linear correlation of multiple parameters

I tried to search for this problem but I don't know what exactly I'm looking for. I found some empirical parameters that correlate but not linearly. An example follows: $Y_1$ and $Y_2$ are the values ...
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### Unable to comprehend results of principal component analysis

(Image below) Image shows the principal component analysis of two points {(1,3), (3,1)}. u1 and u2 are drawn which are corresponding eigenvectors after PCA. The points follow a normal distribution N(0,...
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### Finding the area under a 5th degree polynomial curve given the polynomial fitting?

Using an outdated graphing program, I have a 5th degree polynomial fitted curve for my data (protein level in a treatment). I would like to find the integral of the curve given I only have the 'p0-p5' ...
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### How can I interpret joint and conditional entropies?

Say I have three variables, X,Y, and Z. Joint Entropy of X and Y is greater than joint entropy of X and Z, what does it mean? and Similarly, conditional entropy of X and Y is greater than conditional ...
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### Probability distribution database

Is there some kind of probability distribution database? Very often I'm faced with a problem of fitting a distribution to data. And it also happens very often that exponential-looking data doesn't fit ...
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### RMSE for shifted series

I am facing the problem to compare a series of simulations to a set of observations. Normally I would employ the Root Mean Square Error (RMSE) as goodness-of-fit measure to understand which is the ...
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### Is there a tool for finding invariant features on data?

I don't know how to make a specific question, because that's what I don't know and I'm asking for. I don't even know what tags should I put on this question. If I knew, I would have the answer. I ...
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### How generic is the “Unix file permission” algorithm?

In data analysis tasks, binary variables are usually encoded as $1$s and $0$s. In data sets with multiple binary variables, it is often necessary to create "interactions" of binary variables that can ...
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### What is KL-Divergence? Why Do I need it? How do I use it?

I am currently studying KL Divergence. But It seems very confusing that I don't maybe understand why do I ever need it and what is that for? As I have been reading stuff about Mutual Information, it ...
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### Discrete data, indepedence etc.

I'm trying to understand something that might seem basic to some but its really screwing with my mind. Imagine a set of $N$ observations of 2 variables. One variable $L$ is one of $A,B,C$ and one $I$ ...
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### What methods can I use to model a seemingly chaotic set of values? [closed]

If I have a graph/set of data, what methods can I use to model the data to predict a likely next set of values? For example, given the following numbers [ 2, 4, 5, 2, 1, -1, -2, 0 ], are there some ...
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### Model for headphone quality as a function of price

I've looked for any mathematical model that shows headphone quality as a function of the price of the headphones, but have not found anything yet. Of course, "quality" is quite subjective, which could ...
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### Prediction for time series

Suppose we have several weeks (say, 30) in a row and number of advertisements sent on e-mails on each week and number of the following orders of the product. How can I estimate the necessary number ...
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### data compression average number of bits

consider the following data file. AAACAAABAAACAAADAAAE implement a Huffman code to compress this file. What is the average number of bits per symbol?
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### How to make a covariance matrix from multiple observations of different objects?

I have $N$ objects. From each object, I sample $M$ values $(x,y)$ like so: ...
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### Creating Formula from Data Series

I have a power-law-ish data series and need to back my way into a formula for it, such that it can be generated for any number of points. This is the n=20 version (value rounded to nearest 0.25). ...
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### Best fit with unknown functional form

I have data from a simulation of a certain function $F(x)$ for a discrete set of values $\{x_i\}$. I know that $$F(x) = A \ f(x) + B \ g(x)$$ where $A,B$ are (real, positive) constants and $f,g$ ...
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### Curve fitting: How to identify the appropriate function for a beat-like phenomena?

I have a time series data which shows some beat like behaviour. The envelope does not look exponentially decreasing, as it is impossible from a physics point of view. The envelope is likely to be a ...
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### Getting a feel for the Normal-Inverse-Wishart conjugate prior to multivariate normal distribution

I am trying to get a feel for the Normal-Inverse-Wishart conjugate prior, which I have started to use, sparingly, in my work, where I am trying to cluster multivariate normal data. As Wikipedia ...
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### Spectral relaxation of k-means clustering

I am working on a presentation on Spectral relaxation of k-means clustering (http://papers.nips.cc/paper/1992-spectral-relaxation-for-k-means-clustering.pdf) and I am a bit stuck. I understand ...
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### Tropical geometry: practical applications?

In 1960, E. Wigner published a paper entitled "The Unreasonable Effectiveness of Mathematics in the Natural Sciences". Theoretical mathematical structures pave the way to further advances and ...
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### What is trend analysing

Hi I'm just started learning DFA for stochastic processes and I faced to the "trend".I've looked around the internet about trend analysing but still I don't understand it completely.can you define "...
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### likelihood function when data and model share a common parameter

I'm having some conceptual difficulty with how to describe, and deal with, a problem related to constructing a likelihood function that will be used to fit a model to data. Sorry in advance if I ...
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### Alternatives to Shephard interpolation?

I am a chemist, so I have little experience in the field of math. My program is that I have a set of points (approx. 20000) in some larger dimensional space (like 10-20 dimensions), and I want to be ...
I want to find the argument $x$ that maximizes $f(x)=\sum_i e^{-(x-d_i)^2/c}$ for some data values $d_i$ and an arbitrary positive constant $c$. I assume that $f(x)$ has only a single maximum (most ...