Fit Definition and 347 Threads

  1. K

    A Function to fit the light transmitted from a cavity

    Hello! I measured the light transmitted from a bow-tie cavity (while scanning the cavity length) and the peak obtained while scanning has the shape in the figure below. It is basically a combination of a Lorentzian, with an exponential decay on the right side and some oscillations on top. What...
  2. K

    I Best fit to an oscillating function

    Hello! I have a plot of a function, obtained numerically, that looks like the red curve in the attached figure. It is hard to tell, but if you zoom in enough, inside the red shaded area you actually have oscillations at a very high frequency, ##\omega_0##. On top of that you have some sort of...
  3. B

    I Fit Triples into Sixtuples in the best way?

    Hi, I am not sure if this can be called directly a mathematical problem but it kind of is: Say we have the list of all (ascendingly ordered) triple with natural numbers from 1-49 (is about lotto 6 out of 49): T={(a,b,c) | a,b,c natural numbers, 1<=a,b,c<=49, a<b<c} Now we are given a subset of...
  4. M

    I Systematic uncertainties in linear fit

    Hello! I have some data points ##(x,y)##, with some uncertainties on y that are statistical ##dy_1## and some systematic ##dy_2##. I want to fit this data using a linear function. How exactly should I deal with the different types of uncertainties? Can I just add them in quadrature and perform...
  5. M

    I Maximum likelihood to fit a parameter of this model

    Hi PF! Given random time series data ##y_i##, we assume the data follows a EWMA (exponential weighted moving average) model: ##\sigma_t^2 = \lambda\sigma_{t-1}^2 + (1-\lambda)y_{t-1}^2## for ##t > 250##, where ##\sigma_t## is the standard deviation, and ##\sigma_{M=250}^2 =...
  6. LCSphysicist

    I Best way to fit three functions

    So I have $$f(x,y,z,t,n) = 0,g(x,y,z,t,n) = 0,h(x,y,z,t,n) = 0 $$ and i need to find the best ##[x,y,z,t]## that fit the data, where n is the variable. Now, the amount of data for each function is pretty low (2 pair for f (that is, two (n,f)), 3 pair for g and another 3 pair for h) The main...
  7. B

    I A few questions about doing a Gaussian Fit

    A few questions about doing a Gaussian Fit : 1) Is gaussian fit and gaussian regression the same thing ? 2) I have a gaussian function that will return a list of gaussian numbers giving an initial list length. So if you input 5 you will get: 1,2,6,4,1. My question is if I have an image and I...
  8. B

    A How to perform a fit with correlated variables

    Hello! I need to perform a fit with several variables and 2 of them are very correlated (above 0.99). The functional form of these 2 variables is something like: ##(p+q)x+qf(x)##, where ##f(x)## contains polynomials and some square roots of x, but the coefficients appearing in ##f(x)## are much...
  9. Buzz Bloom

    I Observations fit poorly with the Standard Model of Cosmology

    Reference: https://scitechdaily.com/breaking-cosmology-too-many-disk-galaxies-a-significant-discrepancy-between-prediction-and-reality/ The following are quotes from the reference. 1. The Standard Model of Cosmology describes how the universe came into being according to the view of most...
    • Buzz Bloom
    • Thread
    • Cosmology Fit Model Standard Standard model
    • Replies: 34
    • Forum: Cosmology
  10. ORF

    Python Binned Maximum Likelihood fit in python?

    Hi, I have been using Python for a while now, but so far for Least-squares fits using curve_fit from Scipy. I would like to start using Likelihood method to fit binned and unbinned data. I found some documentation in Scipy of how to implement unbinned likelihood fit, but I have not managed to...
  11. M

    I Fit a non-linear function to this time series

    I have an experimantally obtained time series: n_test(t) with about 5500 data points. Now I assume that this n_test(t) should follow the following equation: n(t) = n_max - (n_max - n_start)*exp(-t/tau). How can I find the values for n_start, n_max and tau so as to find the best fit to the...
  12. F

    Where does XML fit in relation to website and webpages?

    Hello, I understand that webpages are created using HTML which defines the structure of the document using a finite number of specified tags, like <p>, <head> etc. In XML, the user can create customized tags (as long as certain rules are respected). The XML file recipient must then be able to...
  13. M

    I Error on non-linearity in a linear fit

    Hello! If I have some data points, with error bars on both x and y, and I would like to fit them with a function f(x). How can I write the chi-squared in this case? For errors only on y, I would have ##\chi^2 = \sum_i(\frac{f(x)-y}{\sigma_y})^2##, but I am not sure how to include ##\sigma_x##...
  14. A

    A Correlation between parameters in a likelihood fit

    Hello community! I am facing a conceptual problem with the correlation matrix between maximum likelihood estimators. I estimate two parameters (their names are SigmaBin0 and qqzz_norm_0) from a multidimensional likelihood function, actually the number of parameters are larger than the two I am...
  15. Haorong Wu

    MATLAB How to Fit Nonlinear Equations in MATLAB?

    Hello. I am trying to fit some nonlinear equations. I have some data ##\vec \lambda, \vec n, \vec \kappa ##. Now I would like to use them to fit two equations $$n=n(\lambda ; \alpha, \beta, \gamma)$$ $$\kappa=\kappa(\lambda ; \alpha, \beta, \gamma)$$ where ##\alpha, \beta, \gamma## are the...
  16. A

    Finding the largest ellipse that will fit in a polygon

    Summary:: Questions about finding largest ellipse in polygon Was wondering if someone could help me understand two concepts involved with finding largest ellipse in a polygon? Some background: First, I set up a set of half-plane representations for the example polygon below and as you can...
  17. Ozen

    Help With Shrinking a Circuit/Making it Fit Into a Tight Space

    Attached is the schematic for the circuit. It uses a TPS61042DRBT LED driver along with a PSoC 4000 8pin microcontroller to drive a 10mA LED with push button controls for brightness. The problem is some components, like the inductor and sense resistor is way too large (over 6mm long!). This is...
  18. T

    I Preprocessing FIT Files to Bias and Flat Correction Using Python Script

    I have a list of about 35 fit files, where there are 10 dome flats files, 10 bias files, 10 standard stars files, and 5 target files. Where each file has been filtered with BVI filter. So a third of the dome flat files were taken with a I-filter, a third with V-filter and a third with B-filter...
  19. Whipley Snidelash

    Where do I fit in the history of data compression?

    In 1982 I was given a ZX Spectrum by a Timex employee. It was one of only three English units that had been converted to NTSC from PAL. They worked for Timex but had their own company on the side to write software for the Timex computer and for the spectrum They hired me to do the title screen...
  20. B

    I Which method should I use for a linear fit of data with error on both z and y?

    Hello! I have some data of the form (x,y,z) which I know it is described by a function of the form: ##z=y(a+bx)##, where a and b are parameters to be fitted for. z and y have error associated to them while x doesn't (x is actually an integer going from 0 to 3 for each value of y). I tried to do...
  21. C

    I Akaike Information Criterion Vs Likelihood Ratio Test

    Hello, I want to understand the difference between both goodness-of-fit tests, I would be glad if you could help me: Akaike Information criterion is defined as: ## AIC_i = - 2log( L_i ) + 2K_i ## Where ##L_i## is the likelihood function defined for distribution model ##i## . ##K_i## is the...
  22. M

    I Weird covariance matrix for linear fit

    Hello! I really don't know much about statistics, so I am sorry if this questions is stupid or obvious. I have this data: ##x = [0,1,2,3]##, y = ##[25.885,26.139,27.404,30.230]##, ##y_{err}=[1.851,0.979,2.049,6.729]##. I need to fit to this data the following function: $$y = a (x+0.5)/4.186 +...
  23. Z

    First Fit (FF) requires 10m bins: Why

    Hi, I am having problem in understanding the following text of the book: My solution: If m = 1 then its possible to have 6 bins. All1/7 elements would go into 1 bin. All 6*1/3 items would go into 2 bins All 6 *1/2 items would go into 3 bins. Total = 6 bins It further says: Why First Fit...
  24. B

    I Should I Remove the Outlier Point in My Linear Fit?

    Hello I have these points coming from different experiments: ##x = [-0.3, -0.2, -0.09, 0.01, 0.2]## ##y = [-8.15, -5.20, -3.32, 0., 5.65]## ##y_{err} = [0.1, 0.27, 0.35, 0.09, 0.44]## and I need to fit a straight line to them (based on theoretical arguments). I attached below the obtained...
  25. K

    I Linear fit on the difference of data points

    Hello! I have some data points obtained from a measurement and one of them is defined as the reference point. I need to compute the difference between that reference point and all the others (including itself) and plot the difference as a function of another variable (which doesn't have an error...
  26. K

    I Plot Linear Fit w/ Error Bounds: y=ax+b

    Hello! I made a linear fit, ##y=ax+b##, to some data points and I get the best parameters with their (1 sigma) errors: ##a\pm\delta a## and ##b\pm\delta b##. I want to plot this fit on top of my data points in such a way as to reflect the error on the parameters. The "main" fit is simply...
  27. M

    Mathematica How to Break Up and Simplify Complicated Expressions in C++?

    Hi PF! My question is easiest to show via the following input, the output, and my desired output. input: x^2 + y^2 // CForm output: Power(x,2) + Power(y,2) desired output: pow(pos().x,2) + pow(pos().y,2) I appreciate any help you can offer. Thanks so much! Edit: for what it's worth, I'm just...
  28. T

    MHB The smallest circle that two parts of a semi-circle can fit into?

    So, true story: I made a large circular tortilla. Ate half of it. Then decided to put the rest into the fridge on a smaller plate.I raised the knife to cut the remaining semi-circle in two, and then went : "Hmmmmmmmm...". Anyway, it's in the fridge now with an approximate solution, but I'm...
  29. K

    Mathematica Finding a function to best fit a curve

    Hello! I want to fit a function to the curve I attached (the first image shows the full curve, while the second one is a zoom-in in the final region). Please ignore the vertical lines, what I care about is the main, central curve. It basically goes down slowly and then it has a fast rise. What...
  30. M

    I Chi-squared fit with errors on both x and y

    Hello I have some data points which have errors on both x and y coordinates. I want to fit a straight line to them but I am not sure how to take the error on x into account. Normally, when I have just the error on y, I want to minimize $$\sum\frac{(y_{pred}(x)-y_{measured}(x))^2}{\sigma_y^2}$$...
  31. M

    I How to handle the infinity when making a least square fit for the first point?

    Hello! I have 5 data points with errors associated to them ##y_i \pm dy_i## and the corresponding ##x_i## values (which don't have uncertainties associated to them). I need to calculate the difference between the first of these points, ##y_1## and the rest, and fit a straight line to it...
  32. M

    I How Should You Approach Fitting Multiple Gaussians to Data with Poisson Errors?

    Hello! I have the to fit a curve to the attached data (I plotted it both with and without error bars), where the error bars are Poisson errors i.e. ##\sqrt{N}##, where ##N## is the number of counts in the given bin. I want to fit 3 Gaussians + background and extract the values (and errors...
  33. Wrichik Basu

    MATLAB Forcing the best fit line to pass through a certain point (Octave)

    I have the following code in Octave: h = [29.3 25.3 19.7 16.0 10.9]; v = [0.53 0.47 0.37 0.29 0.21]; plot(h,v,'obk') hold on p = polyfit(h,v,1); y = polyval(p,h); plot(h,y,'-bk') And I get a good graph: I can extrapolate the best fit line using the following code: x = -1:0.01:11; >> y =...
  34. K

    I Take errors into account for a data fit

    Hello! I have some data in which the dependent variable ##y## has, for each data point, an error bar associated with it ##\delta y##. The errors are almost identical for each datapoint, so doing a weighted fit in terms of the errors would not change the results significantly. How can I take the...
  35. R

    Need a cancer to fit a fictional plot

    Summary: For fictional purposes, looking for a cancer which has a very low survival rate but which a patient might be fighting for 1-2 years I'm sure that this is actually a fairly common sub-genre of medical questions, authors asking for a disease to fit a story. I have a lot of side...
  36. W

    Job Skills Can we use OCAI layout to find a good Company Culture Fit?

    Hi, The OCAI format https://OCAI.wordpress.com/2010/05/21 , it seems , has proven effective in terms of describing the culture of companies ( it has quantitative aspects and addresses the dynamic, changing aspect of corporate,company culture.). I am referring to jobs in general. How could we use...
  37. L

    MATLAB To what extent is the fit to experimental data good?

    I have experimental spectrum in which y-axis is intensity values, and x-axis is frequency values. Int - array of experimental intensities (y-axis). w - array of frequencies (x-axis). I know the view of theoretical function that must describe the obtained spectrum. I explicitly set the function...
  38. J

    Which mechanism and which step would best fit the data?

    Homework Statement Two mechanisms are proposed (as seen in the screenshot). Which mechanism and which step as the rate determining step would best fit the data? Homework Equations I think this is more of a conceptual problem ... The Attempt at a Solution I apologise for not strictly...
  39. wolram

    B Why does MOND fit rotation curves so exactly?

    I have been reading this article https://tritonstation.wordpress.com/2018/10/05/it-must-be-so-but-which-must/ so why does Mond fit so well over dark matter models?
    • wolram
    • Thread
    • Curves Fit mond Rotation
    • Replies: 14
    • Forum: Cosmology
  40. BillTre

    240 Mosquitos can Fit into 1 Cubic Centimeter

    and survive for 24 hours. That would be 4.16 cubic millimeters per mosquito! These findings are due to testing of packing methods for shipping mosquitos around for disease prevention (like malaria which is mosquito transmitted.
  41. Jonas Hall

    I Conf.intervals for fitted parameters: divide by sqrt(n)?

    If you fit a parametrized model (i.e. y = a log(x + b) + c) to some data points the output is typically the optimized parameters (i.e. a, b, c) and the covariance matrix. The squares of the diagonal elements of this matrix are the standard errors of the optimized parameters. (i.e. sea, seb...
  42. AchillesWrathfulLove

    News What is a list of job titles that fit this description

    > A person who works on small scale electrical and mechanical systems > The design and construction of such systems > From toys to hand-held devices such as phones What job titles fit this description?
  43. Shivam2112

    I want to fit 2 radiators in parallel....

    What are the downside for it ,also can i fix 2 bike radiators (cross flow) by rotating them by 90 like top to down flow
  44. Wrichik Basu

    MATLAB Troubleshooting Best Fit Line and Distance Calculation in MATLAB

    I have some experimental data, and I would like to plot a graph in MATLAB and also find the best fit line. I also want to find the distance between each point and the best fit line, and if the distance is greater than 1 unit, an error will be shown. For this, I have written a function. Here it...
  45. S

    I Uncertainty of coefficients after a least square fit

    Fitting data to a linear function (y=a0+a1*x) with least square gives the coefficients a0 and a1. I am having trouble with calculating the uncertainty of a0. I understand that the diagonal elements of the covariance matrix C is the square of the uncertainty of each coefficient if there are no...
  46. MichPod

    Does "magnetic charge" fit into vector potential?

    Disclaimer: I am not a physicist, just trying to learn some parts of it in my free time. And I do not mean to propose any kind of "new-theory" with my question. I always thought that Maxwell equations in their differential form for B and E may be reformulated/updated to include a magnetic...
  47. M

    Linear fit, force intercept with X-uncertainties

    I have some experimental data, in this case, we performed a study of the Zeeman effect in Cadmium with the use of a Fabry-Perot inferferometer. The data should fit a straight line, but I would like to force the intercept through the origin since the relation between the wavenumber difference and...
  48. Jakub

    Bi-exponential function fitting in Origin Lab SW

    I can't understand the exponential function fit for this set of data works well: ExpDec2 exponential function fit 0 3,04 10 2,77 20 2,52 30 2,27 40 2,09 50 1,92 60 1,75 70 1,62 80 1,51 90 1,43 100 1,36 110 1,29 120 1,24 130 1,19 140 1,14 150 1,09 160 1,05 170 1,02 180 0,99 190 0,97 200 0,95 210...
  49. kvothe18

    I Linear fitting in physics experiments with errors

    Hello! I have a question that maybe has to do more with Mathematics, but if you do experimental physics you find it quite often. Let's assume that we want to measure two quantities x and y that we know that they relate to each other linearly. So we have a set of data points xi and yi...
  50. Buzz Bloom

    I How do I determine if improving a fit is significant?

    I have forgotten how to do a goodness of fit test for the problem below. I have not done this type of problem for several decades, and I hope someone can help me refresh my memory. I looked up the chi-squared test, Student t-test, and Fisher’s exact test on Wikipedia, but I found those articles...