Questions on (linear or nonlinear) regression, the fitting of functions that best approximate empirical data.

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68 views

Intuition and the math behind normalization

What exactly is the purpose of normalization. From what I read, it is to adjust two different sets of values so you can compare them, but I don't understand why, nor the math behind it. Could anyone ...
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2answers
84 views

Is there a way to fit an even function using only odd functions?

I was wondering if there is a way to make an infinite series of odd functions equal to an even function. For example, I would like to know if the next equation is valid ...
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1k views

Examples of logistic regression and multinomial logistic regression

I've been studying to understand the concept of logistic regression and I think I understand the idea more or less, but there are still some gaps to fill. What I'm looking for is an example of ...
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3answers
4k views

Fitting exponential curve to data

If I have a collection of data points that follow an exponential curve relationship, how can I manually construct the equation that defines the best-fit exponential curve for the data?
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1answer
56 views

How to derive the equations in 3:19-3:30 provide in a MIT opencourse ware lecture about the least square method?

How to derive the equations in 3:19-3:30 provide in a MIT opencourse ware lecture about the least square method? Link: http://www.youtube.com/watch?v=YwZYSTQs-Hk Thanks in advance!
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526 views

degrees of freedom for linear regression

If you have a reduced model with $H_0:\beta_1 = 1$, $H_a: \beta_1 \neq 1$, then the reduced model is: $$Y_i = 1X_i + \beta_0 + \epsilon_i$$ Are the degrees of freedom for the error term SSE $n-1$?
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832 views

Finding the change point in data from a piecewise linear function

Greetings, I'm performing research that will help determine the size of observed space and the time elapsed since the big bang. Hopefully you can help! I have data conforming to a piecewise linear ...
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2answers
6k views

Find equation of curve fit programmatically in Matlab?

In MATLAB, when you plot something, there's a tool available which is called "curve fitting". And if you have a set of data points and a linear correlation, this tool will easily come up with an ...
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30 views

Optimizing Independent Variables to Maximize Dependent Variable

I looked around online and couldn't find anything that was answering my question so I thought I would take to the stack! I'm interested in knowing if there is a statistical or mathematical way of ...
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2answers
418 views

Prove $SST=SSE+SSR$

Prove $$SST=SSE+SSR$$ I start with $$SST= \Sigma (y_i-\bar{y})^2=...=SSE+SSR+ \Sigma 2( y_i-y_i^*)(y_i^*-\bar{y} )$$ and I don't know how to prove that $\Sigma 2( y_i-y_i^*)(y_i^*-\bar{y} )=0$ a ...
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26 views

Would it be any concern if we find correlation between intercept and other regression coefficients?

During a multiple linear regression analysis, I found correlation between intercept (beta-0) and two of the other regression coefficients. Is there any problem or concern in this case? If no, please ...
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44 views

Polynomial best fit line for very large values

not only are the x values large, the difference between them and the y values is huge. My data points: 22353120,720 24448725,671.427053270323 26544330,634.312274868634 28639935,566.291966792026 ...
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56 views

Multiple linear regression

For a homework we have to determine the effect of a predictor variable on an outcome variable using simple linear regression. We have lots of data (about 300 variables) and we may include some other ...
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1answer
136 views

Proof that a and b in linear regression are random variables

Does anyone know how to prove that the variables $a$ and $b$ that are used in linear regression are random variables? For me the assumption would be that these are dependent on the values of $x$ and ...
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2answers
106 views

Linear Regression to quadratic function

What is the optimal linear regression (w and w/o y-intercept) for a quadratic curve w.r.t. mean square error. Mathematically speaking: Given, $$y = x^2$$ for $$x = [-a,a]$$. What is the best ...
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1answer
393 views

What is the difference between a polynomial regression and a generalized linear model?

I have seen that a polynomial linear regression can have this form: $y = c_0 + c_1 x_1 + c_2 x_2 + \dots + c_k x_k $ but I have read that the general lineal model which is a form of the multiple ...
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2answers
86 views

What is the equation that fits this curve?

I have a curve that looks like this (it's cyclical): Curve I can get a partial fit by fitting a 3rd degree polynomial, but I have a feeling there must be a better fit (something that involves sin ...
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2answers
382 views

Normal Distribution from Standard Deviation?

So I have a data set $(x_{1},y_{1}), (x_{2},y_{2}),\dots,(x_{n},y_{n})$ and from it I have the values of $\sum x$, $\sum x^{2}$, $\sum y$, $\sum y^{2}$, $\sum xy$. My question is, how do I find a ...
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1answer
84 views

$(X^tX)^{-1}$ when $p>>n$

For the $n\times p$ matrix $\mathbf{X}$, is there any use in approximating $(\mathbf{X}'\mathbf{X})^{-1}$ when $p>>n$? If so, what information might this tell us? I understand when $p<n$, ...
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3answers
127 views

Middle line between points

How can we calculate LINE that most fit the points T1(1,0) T2(2,0) T3(-1,1) T4(0,1) $x= (1,2,-1,0) $ $y= (0, 0, 1, 1) $ $1= (1, 1, 1, 1)$
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1answer
118 views

Calculating the regression equations

I have four data points $(1,2), (2,4), (3,5), (5,7)$ and Im looking for the least squares regression line that best fits them. I use the normal equation $A^tAx=A^tb$ in this form - ...
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1answer
1k views

Construct / find the simplest function based on data

Let's say I have these 7 natural numbers (all between 0 and 255): 255, 23, 45, 32, 87, 52, 146 How can I find a function F(x) that, once computed, gives me back ...
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674 views

Simple non linear fitting question(Least Squares Fitting--Exponential) [duplicate]

Possible Duplicate: easy to implement method to fit a power function (regression) I have the following simple function: $h = cV^n$ h and V being the variables and $c$ and $n$ are ...
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1answer
132 views

problem constructing an equation that connects variables

need a suggestion/advice/inputs from the mathematicians here. I have collected data of number of instructions/sec executed by a processor every second, number of loads/stores performed every second ...
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1answer
29 views

Variance- covariance matrix

Consider $H$ denotes hat matrix and $e$ denotes residual. In the book Applied regression Analysis by Draper/Smith, it is written that : $\mathbb V(e_i)$ is given ...
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1answer
13 views

Dummy recoding for more than two categorical variables

Say I am doing a study with 3 different types of fruit and I want to make a regression depending on the type that tries to predict the amount sold. I know that I could make 2 dummy variables: orange ...
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1answer
26 views

Is the Inverse of the Vectorised Solid Angle Equation for $n$ Circular Discs Continuous?

I have a continuous function$^{*1}$ that takes in 3 arguments, and returns 24 outputs. I want to know if the inverse of this function is continuous. The 3 input arguments are the x, y, and z position ...
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1answer
15 views

Linear regression with normalized variables

Suppose I have two variables X and Y such that mean(X) = 0 = mean(Y) and sd(X) = 1 = sd(Y). The slope of the linear regression line for Y vs X is cov(X,Y)/var(X) = corr(X,Y) since X and Y are ...
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2answers
61 views

Plotting an Ellipse after an Ellipse Fit

I wonder if someone can assist my understanding as I'm a bit stumped with this... I have taken the following (x,y) data which lies roughly on an ellipse: $$ \begin{pmatrix} 0.000234491 & 6855810 ...
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1answer
32 views

Calculating R-squared with duplicate data

I have the following question regarding the proper usage of R-squared value. Say I have an equation, that predicts energy consumption for the month of a building. One of the input variables accounts ...
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1answer
11 views

Meaning of $\mathcal{I}_t$ in assumption $E[u_t\mid\mathcal{I}_t]$ of distributed-lag model

When considering \begin{equation*} y_t = \beta_0 + \beta_1 x_t + \ldots + \beta_r x_{t-r} + u_t \end{equation*} an assumption made is \begin{equation*} E[u_t\mid\mathcal{I}_t] = 0 \end{equation*} ...
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1answer
36 views

Wolfram Exponential Fit not match as formulas

I am using WolframAlpha Exponential-Fit formulas to find equation of Exponential Regression http://mathworld.wolfram.com/LeastSquaresFittingExponential.html but after implementation, I tested with a ...
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1answer
28 views

clustering of singular values

let us consider following graph of singular values i want to make some kind of clustering of these data,namely to seperate main components from non main components,let say signal components ...
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1answer
41 views

Equations for Cubic Regression

So, I'm making a simple program for drawing graphs, and I'm looking at making some simple best-fit curves using some basic regression analysis. I've happily got linear and quadratic regression working ...
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1answer
58 views

regression on circular data

How would one design a regression where the dependent variable is measured in degrees on a circle? The dependent variable is on the range [0, 360), and the independent variables are demographic ...
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1answer
34 views

What's the “ridge” in Ridge Regression?

In normal least squares, we try to find $\hat\beta$ which minimizes $$\|y-X\beta\|^2$$ Ridge regression expands this to "penalize" certain values of $\beta$ via a matrix $\Gamma$: ...
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48 views

Variance of Coefficients in a Simple Linear Regression

I have a linear regression model $\hat{y_i}=\hat{\beta_0}+\hat{\beta_1}x_i+\hat{\epsilon_i}$, where $\hat{\beta_0}$ and $\hat{\beta_1}$ are normally distributed unbiased estimators, and ...
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1answer
27 views

Regression towards the mean?

I am upset with what examples testing "regression to the mean" seem to allude to: People claiming to have "ESP" take a test, and A's score was 2 standard deviations above the mean, whereas B's score ...
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3answers
37 views

Different Regression Lines?

Hi quick question with regression. If the coefficients of a simple regression line, B0 and B1, are the same then why are the regression lines of y on x and x on y different given the condition r^2 ...
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1answer
32 views

Combine linear models of different sets of data.

I'm working on a large data set D that can be partitioned into some disjoint subsets D1, D2, ..., Dn. For each subset Di, I have a linear model Mi that minimizes the residual error for data in Di. ...
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1answer
28 views

Morphing $\beta_1$ into a different form (OLS question in Statistics)

I am currently studying Simple Linear Regression and I have successfully proven to myself how $\beta_1$ and $\beta_0$ are derived. However, I have been stuck on a seemingly simple problem (I'm sure ...
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2answers
45 views

Scaling data into $[-1,1]$

I have a data in the matrix for: \begin{bmatrix} 1 & 2 & 3 & 9 & 6\\ 8 & 2 & 7 & 4 & 6 \\ 1 & 2 & 8 & 7 & 4 \end{bmatrix} Each row corresponds ...
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1answer
27 views

Unexplainable determination coëfficiënt

I have a series of data (more specific, they are coördinates of a package attached to the end of a mini level-luffing crane. The "flightpath" is linear and horizontal.) Now when I plot the data: ...
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1answer
536 views

Convert nonlinear regression equation to a linear regression equation

The question is: "Show how the nonlinear regression equation y=aX^B can be converted to a linear regression equation solvable by the method of least ...
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1answer
64 views

Weird formula for linear regression

I'll try to make the matter as clear as possible given the circumstances. My boss asked me to look at an old report a former employee wrote around a couple of months ago. Apparently the report ...
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116 views

Simple linear regression - understanding given

The question is to fill out the missing numbers (A-L) of a simple linear regression model. I am having problems with converting and interpreting the given table in terms of variables. Would it be ...
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65 views

Logistic regression with interactions

I'm supposed to do a model using logistic regression. So I have a series of $N$ observed data points each of which consists of $m$ explanatory variables $x = (x_{1,i}, ... , x_{m,i})$ and associated ...
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388 views

Mean response in linear regression

What does mean response in linear regession mean? I don't understand the definition given in wikipedia. This is the definition: Mean response is an estimate of the mean of the $y$ population ...
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1answer
130 views

Machine Learning, why not use matrix multiplication instead of gradient descent?

If we want to minimize our Cost function for a given set of data, why do we use gradient descent and continually guess values until we find a min value for theta when when can just use matrix ...
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146 views

How do I solve the weighted normal equations?

I am trying to solve the normal equations for a 3D LSE of a general quadric: $$ z = ax^2 + bx + cxy + dy^2 + ey + f$$ Write as a vector equation: $$ \vec{z}= \bf{X}\vec{\beta}$$ where the 'ith row ...