Interpolation Definition and 136 Threads

hi all I am new learner on fortran. as a part of practice, i am trying to translate below equation into fortan. I have read about interpolation, but couldn't understand it well. Can anyone here help me to translate interp1 funtion into fortran90...thank you very much. for i=ja:jb...

Hello! :) I am looking at the proof of this theorem: Let $f \in C^{1}([a,b]),P:a=x_{0}<x_{1}<...<x_{n}=b $ uniform partition of $[a,b]$.Then there is exactly one function $s \in S_{3}(P)$ so that $s(x_{i})=f(x_{i}),i=0,...,n$ and $s,s',s''$ continuous at...

Homework Statement Let t_j=j/100, a_j=j, b_j=-j, for j=0,1,...,99. Define f(t)=\sum\limits_{k=0}^{99} (a_k\cos(2\pi kt)+b_k\sin(2\pi kt)) Determine the values of c_l, d_m for l= 0,...5, m=1,...,4, so that P(t)=\frac{c_0}{2}+\sum\limits_{k=1}^4 (c_k\cos(2\pi kt)+d_k\sin(2\pi kt))+c_5\cos(10\pi...

Homework Statement I'm trying to derive the coefficient matrix (a) of a parabolically terminated cubic spline. This is the matrix of coefficients ##a_i \rightarrow a_n## where n is the number of data points provided. With this matrix you can find all the other coefficients (b and c) that...

Homework Statement I'm trying to write an efficient bilinear (2D)-interpolation, after reading some recipes, as a fortran-mex for Matlab that is used extensively throughout a long algorithm of solar image processing, and therefore is one of my main bottlenecks. I'm not a Fortran expert and...

Hi, I'd sincerely appreciate it if someone were willing to review the few lines of MATLAB code below and indicate why they don't quite yield the expected output. Homework Statement I am asked to generate using MATLAB approximated values of f(x)=cos(x) at nodes x+h,x-h with random errors...

Hi, Homework Statement A quadratic piecewise interpolation is carried out for the function f(x)=cos(πx) for evenly distributed nodes in [0,1] (h=xi+1-xi, xi=ih, i=0,1,...,πh). I am asked to bound the error. Homework Equations The Attempt at a Solution I believe the error in this case is...

Hi, Homework Statement Interpolation for the function f(x)=cos(x) for evenly distributed values of x in [0,π] (h=xi+1-xi, xi=ih, i=0,1,...,πh) is carried out. Also known are f(xi). I am asked to determine the value of h so that the interpolation's error is ≤ 5*10-8. Homework Equations...

I have a time series of data that I want to interpolate using a piecewise linear function. The lengths of the linear pieces should be adaptive such that the maximum error of the points in the interval does not exceed a predetermined value Max_R. I guess the specification boils down to: Find a...

Homework Statement Consider the Lagrange Polynomial approximation p(x) =\sum_{k=0}^n f(x_k)L_k(x) where L_k(x)=\prod_{i=0,i\neq k}^n \frac{x-x_i}{x_k-x_i} Let \psi(x)=\prod_{i=0}^n x-x_i. Show that p(x)=\psi(x) \sum_{k=0}^n\frac{f(x_k)}{(x-x_k)\psi^\prime(x)} Homework Equations None...

This is not a homework problem. I am given the equation of two lines at different temperature gradients for (suction line temp,suction line pressure) => (x,y) At outdoor temp 95*F; y=.41667x+54.1667 At outdoor temp 85*F; y=.4231x+50.3846 I need to find suction line pressure for 72*F temp...

What does it mean when you are given a pressure and temperature of refrigerant and the values in the tables are not in the same row? Like 600 kpa and 25 degrees celsius. 600Kpa should be around 21.-- degrees.

Anyone familiar with the bivariate interpolation method developed by Akima? I've been reading H. Akima, Commun. ACM 17, 18 (1974) and trying to implement his method, but he actually doesn't describe how to do the interpolation! The formulas for calculating the derivatives at each point are...

Hi guys, I was solving this problem using backward interpolation https://dl.dropboxusercontent.com/u/49829206/1.PNG and I got this solution https://dl.dropboxusercontent.com/u/49829206/3.PNG but What I don't get is that how come is the the forth difference is constant while it not in real...

Folks, I am puzzled how the linear interpolation functions (see attached) were determined based on the following equation below ##\displaystyle...

This sort of came up the other day: Given a sequence of monotonically decreasing points, a_n, such that a_n \rightarrow 0 does there exist an analytic f on ℝ such that f(n) = a_n ? I figured there should be some sort interpolation theory on this, but I haven't found anything...

The wikipedia article on bicubic interpolation appears to describe how to arrive at an equation for bicubic interpolation, but I cannot decipher it. Using the derivatives described I don't understand how to arrive at the relevant equation from the coordinates of the point and the values of the...

Hi there. I have a problem regarding interpolation between lines. I have to say that I have never done it before and I can't find relevant info on the internet, so I am asking for your help. the graph in question can be found here: http://s9.postimage.org/kmj94nexb/physicsforum.png I do...

If a cubic function satisfies f(0) = -32, f(1) = 0, f(3) = 10 and f(4) = 0, use cubic interpolation to estimate f(2) I'm not sure how to approach this since I have only ever done quadratic interpolation and linear interpolation, is it just an extension of the lagrange interpolating...

here is the answer: 36/60 = x/.8660 60x = .8660 x 36 60x = 31.176 x = .5196 however, where does the value: 0.8660 initially come from? any help would be appreciated

I'm trying to find the tri-linear interpolation parameters of a point C within a hexahedron of 3d vectors (C000, C100, C010, C011 etc) You could call this "inverse tri-linear interpolation" Ive used the same variable names as this wikipedia article...

Homework Statement Let D:R[x]->R[x]be the differentiation operator D(f(x))=f'(x),prove that e^tD(f(x))=f(x+t) for a real number t Homework Equations application of Lagranges interpolation The Attempt at a Solution i don't know how to begin or construct the proof here

[FONT=Cambria]Problem: [FONT=Cambria]Use the Lagrange interpolating polynomial of degree three or less and four digit chopping arithmetic to approximate [FONT=times new roman]cos(.750) using the following values. Find an error bound for the approximation. [FONT=times new roman]cos(.6980) =...

Folks, How do determine whether the derivative of a quadratic interpolation function ##ax^2+bx+c## is continous/discontinous in the context of the following We have a a true solution approximated by 2 quadratic interpolation functions ie, The approximation function f_1(x)=ax^2+bx+c...

Hi, I'm trying to interpolate a data set of classical trajectories, but I'm having trouble because the data is basically a multivalued function. The data maps out a periodic function: for every x value, there are about 7 y values. Does anyone have any advice as to how to approach this...

Hello! I am wondering if it is possible to establish a relationship between three sets of points (x,y,z) by interpolating. Basically i need a function that takes x and y and gives me a z that matches the following points: 130 472 5 130...

I hesitated between posting this in the Mathematics forum or here, but since it's fairly applied, I chose this place. Sorry if it should've gone somewhere else. I posted another thread earlier (https://www.physicsforums.com/showthread.php?t=599737), about having trouble finding the quaternion...

For Refrigerant 134a at T = 60C and v = 0.072 m3/kg, determine pressure in kPa. the v is in superheated region so I have a mini table look like in the picture I've added there I need to do a double interpolation but don't know how. the anser for p is: 3.63Kpa. Thanks

Hi All, I'm working on coding some 2-D interpolation techniques. With wikikepdia's help, I've managed blinear interpolation. What other techniques are out there? Please tell me a little about how your favourite technique works. I've read about higher order methods, using more...

Homework Statement (a) If x_{1},\ldots, x_{n} are distinct numbers, find a polynomial function f_{i} of degree n - 1 which is 1 at x_{i} and 0 at x_{j} for j \ne i. Hint: the product of all (x - x_{j}) for j \ne i is 0 at x_{j} if j \ne i. This product is usually denoted by \prod_{\substack{j...

Hi I have a data set of the form: data = {{0, 0}, {1, 1}, {2, 2}, {3, 20}, {4, 1}, {20, 1}, {21, 1}, {22, 0}}; This data set is a probability density function (PDF), and I need to be able to integrate it from 0 to some x<22. I thought that I would use an interpolating function for...

suppose I have a function f(x) which I know increases as x. I'm trying to combine a for loop and if statement x(1)=a; x(2)=b; x(3)=(a+b)/2; for i=3:n if f(x(i)) > A x(i+1) = (x(i-2)+x(i))/2; else x(i+1) = (x(i-1)+x(i))/2 end end this method works for x(4), the rest come with...

I have performed interpoaltion of applied pressure from one mesh (mesh of tetra elements) to another mesh (mesh of brick elements). I have done the interpolation. I want to introduce some checks if my interpoaltion is rightly done.. Please can anyone advise what could be the checks that...

Hallo, \Gamma(t) is a function that i can know only at dicrete points and appears in this integral: \int\Gamma(t) * tan (\Gamma(t)*t + \varphi) My question is now, which could be the best interpolation of \Gamma(t) that would allopw an exact integration? Thank you very much in advance

Hello, I have the following points that need to be fitted with a curve: (1,20);(2,4);(5,3) I'm wondering how to use the http://en.wikipedia.org/wiki/Lagrange_polynomial to do this. If possible, can these points be fitted with a cubic function? I tried to fit a cubic to this, but...

1) Feed water enters a boiler at 172.52 degrees Celsius. The boiler produces super heated steam at 5600kpa and 472 degrees Celsius. The boiler efficiency is 82%. Find the Heat required by fuel. 2) I interpolated the value given for feed water and super heated steam. h@5600kpa 472 degrees...

Homework Statement Prove I=T1+T2+...+Tk Where Ti=pi(T) Homework Equations T is kxk pi(x)=(x-c1)...(x-ck) is the minimal polynomial of T. pi=\pii(x)/\pii(ci) \pii=\pi(x)/(x-ci) To evaluate these functions at a matrix, simply let ci=ciI The Attempt at a Solution From lagrange interpolation...

If each spline is given in the form of gi(x) = ai(x-xi)3 + bi(x-xi)2 + ci(x-xi) + di where i = 1 to N for N+1 data points. Then given that b1 and bN+1 are zero (because the second derivatives are zero at the endpoints, due to this being a natural cubic spline), then there are N-1...

Working with functions defined by "Interpolation" in Mathematica Hello, Just perhaps a simple question for a Mathematica expert: I have a function of two variables f(a,b) defined using Interpolation option in Mathematica. I am wondering how to determine the value of one of the variable...

Homework Statement Find the polynomial p(x) of degree 20 satisfying: p(-10) =p(-9) = p(-8) = ...=p(-1) = 0 p(0) = 1 p(1) = p(2) = p(3) = ...p(10) = 0 Homework Equations L(x) := \sum_{j=0}^{k} y_j \ell_j(x) The Attempt at a Solution i tried using the formula above: a =...

I have this function (1-6*x^2)^-1 and i want to polynomial interpolation (lagrange and spline) in 21 equidistant points [-1,1] I made this function x =linspace(-1,1,21); y = (1-6*x^2)^-1; z=[-1:0.01:1] c=polyfit(x,y,20) p=polyval(c,z) s=spline(x,y,z) plot(z,(1-6*x^2)^-1, z, p, z, s)...

hi i need some help with a problem I'm dealing with i have a text file of this format 01 08 2002 12 45 26.7 01 08 2002 13 00 27.8 01 08 2002 13 15 27.0 01 08 2002 13 30 28.2 the last being the temperature and i need to interpolate some missing elements using not only the values...

Hi, I'm trying to create an interpolated volume from two surfaces. Let me explain exactly what I'm doing. I am trying to obtain a rough estimate for the temperature in a certain geographical area and at depth. I have the temperature of the rocks at the surface in the form T1=T(x,y,z) where z...

I have to interpolate a function between a small number of points n (say, 3-5), at which I know both the value of the function and its first derivative. Normally, this would be a good candidate for polynomial interpolation. The only problem is that at the first point the function is only...

I want to interpolate a function between the points A, B, C. At A and C I only know the value of the function, but at B (lying between them) I also know the function's first and second derivatives. How would you interpolate between these points?

Hi, I have a 3D gridded ( Nx,Ny,Nz : integers, respectively, size of the grid in x,y and z direction ) which contains the charge distribution of an atom, say Hydrogen, and I would like to simulate the charge density of another structure, in easiest case Hydrogen dimer. (H2) To accomplish my...

Hello everyone, I am using the bicubic kernel described here ( http://en.wikipedia.org/wiki/Bicubic_interpolation#Bicubic_convolution_algorithm ) to interpolate my image after applying some transformations. I an using the matrix kernel described here with a = -0.5. Now, what I also...

Problem: We want to calculate a polynomial of degree N-1 that crosses N known points in the plane. Solution A: solving a NxN system of linear equation (Gauss elimination) Solution B: construction from Lagrange basis polynomials. One of my professors said that the first solution is...

I've run into a problem programming a computer simulation. I have a discrete grid of values and a point an the middle with a value and I need to take the value and put it into the grid. I've been working on the 1 dimensional problem, and I can't get it. I know it's something simple I'm missing...

Hey guys, I got this assignment last week and have been doing every bit of research I can to try to figure out what I am supposed to be doing. I have found a lot of cubic spline interpolation (csi) write-ups including one on here but we don't have a book in this class to help understand how to...