Questions tagged [interpolation]

Questions on interpolation, the estimation of the value of a function from given input, based on the values of the function at known points. It is necessary because in science and engineering we often need to deal with discrete experimental data.

Interpolation is a useful mathematical and statistical tool used to estimate values between two points on a line or curve.

What Is Interpolation?

Interpolation is the process of deriving a simple function from a set of discrete data points so that the function passes through all the given data points (i.e. reproduces the data points exactly) and can be used to estimate data points in-between the given ones.

To help us remember what it means, we should think of the first part of the word, 'inter,' as meaning 'enter,' which reminds us to look 'inside' the data we originally had.

Applications: This tool, interpolation, is not only useful in statistics, but is also useful in science, business or any time there is a need to predict values that fall within two existing data points. It is also used to simplify complicated functions by sampling data points and interpolating them using a simpler function. In the mathematical field of numerical analysis, interpolation is a method of constructing new data points within the range of a discrete set of known data points. In engineering and science, one often has a number of data points, obtained by sampling or experimentation, which represent the values of a function for a limited number of values of the independent variable. It is often required to interpolate, i.e., estimate the value of that function for an intermediate value of the independent variable.

The details, techniques, and precise meaning of interpolation depend heavily on the sub-discipline of mathematics, therefore you are encouraged to use additional subject tags such as , , , or when appropriate.

1995 questions
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Spatial Interpolation for Irregular Grid

How would I interpolate to a point P if I have four points around it such that: Q1 = (x1,y1), Q2 = (x2,y2), Q3 = (x3,y3), Q4 = (x4,y4) If the coordinates formed a regular 2D grid I would use a bilinear interpolation, but I don't think I can use it…
Travis
  • 425
12
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2 answers

Generalization of $\frac{x^n - y^n}{x - y} = x^{n - 1} + yx^{n - 2} + \ldots + y^{n - 1}$

I thought about a generalization for the formula $$\frac{x^n - y^n}{x - y} = x^{n - 1} + yx^{n - 2} + \ldots + y^{n - 1}$$ It can be written as $$\frac{x^n - y^n}{x - y} = x^{n - 1} + yx^{n - 2} + \ldots + y^{n - 1} = \sum_{i + j = n - 1}x^iy^j$$ So…
darkl
  • 322
10
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2 answers

How does sinc interpolation work?

Every now and then I come across mention of sinc interpolation. Trying to read up on it, I have yet to get what it's about. I have done basic DSP work, have programmed stuff using FFT (using just a rectangular window on the data which i know is…
Alan Wolfe
  • 1,259
7
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1 answer

Interpolating point on a quad

I have a quad defined by four arbitrary points, A, B, C and D all on the same plane. I then have a known point on that quad, P. I want to find the value of 's' as shown in the diagram above, where t and s are parametric values in the range (0, 1)…
andygeers
  • 283
7
votes
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2D array downsampling and upsampling using bilinear interpolation

I am trying to understand how exactly the upsampling and downsampling of a 2D image I have, would happen using Bilinear interpolation. Now I am aware of how bilinear interpolation works using a 2x2 neighbourhood values to interpolate the data point…
7
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2 answers

How to draw a smooth curve through given 2D points.

Let me ask about spline functions. I tried spline() function of Octave then I found it was almost I wanted , to draw a smooth curve through given 2D points. But for some points data , it plots unexpected lines. I think it does because each my data…
5
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1 answer

How to non-linearly interpolate between 4 values

I'm looking for a non-linear way of interpolating between 4 values within a games engine. I have a unit square abcd. It has a different value for each edge ABCD. Within that square there is some point x. I also have exact position of x within that…
Kromster
  • 173
5
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1 answer

How to interpolate a sequence?

I have an infinite sequence (see the graphic) which I want to interpolate with an analytic function. Polynomial interpolation fails due to Runge phenomenon. What else can I do?
Anixx
  • 9,119
4
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2 answers

2D cubic B-splines

I have been looking at B-splines to interpolate points. Having 1-D B-splines makes perfect sense to me, but haven't been able to find something that explains 2-D B-splines well for me nor provide me an example. Suppose I wanted to interpolate…
4
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0 answers

Interpolation between curves

I am trying to do a 2D interpolation between two curves as you can see from the attached picture. where $a$ is a varrying paramter. $f_{a_1}$ and $f_{a_2}$ are known, or at least I can perform interpolation along them. The desired point is…
4
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Can I use this method in Lagrange interpolation problem?

I want to find third degree Lagrange polynomial for these four points:$(1,2),(2,9),(3,28),(4,65)$. I know how to use formula to find that. but I want to know whether this alternative method is ok or not: Suppose we have…
Etemon
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4
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Why is it not recommended to use the basis $\{1, x, x^2 , \ldots , x^n\}$ to find the interpolating polynomial?

Why is it not recommended to use the basis $\{1, x, x^2 , \ldots , x^n\}$ to find the interpolating polynomial?
4
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Lagrangian interpolation

I have a high-school student doing a modeling project using interpolation. (Hopefully someone understands what I mean without having to write out explicit examples, as I only have screenshots.) When fitting polynomials of order (n-1) to n points, I…
Cliff
  • 143
4
votes
2 answers

Finding the formula of an nonlinear function

Is there any way, if given multiple points and you wanted to find the equation of the graph where these points lie, how would you find out: First off equation is it? Line, Parabola, Hyperbola, etc? Second, how do you find the equation of this…
Sean
  • 461
3
votes
3 answers

Stuck with integral

Having this: $\int x\sqrt{1-x^2}dx$ Substitution: $t = 1-x^2$ $dt = -2xdx => dx=\frac{-2x}{dt}$ So: $$\int x\sqrt{1-x^2}dx = -\int x t^\frac{1}{2}\frac{2x}{dt} = -\int \frac{2x^2 t^\frac{1}{2}}{dt} = $$ ...but here I stuck... I've tried…
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