# What is Parameter: Definition and 392 Discussions

A parameter (from the Ancient Greek παρά, para: "beside", "subsidiary"; and μέτρον, metron: "measure"), generally, is any characteristic that can help in defining or classifying a particular system (meaning an event, project, object, situation, etc.). That is, a parameter is an element of a system that is useful, or critical, when identifying the system, or when evaluating its performance, status, condition, etc.
Parameter has more specific meanings within various disciplines, including mathematics, computer programming, engineering, statistics, logic, linguistics, electronic musical composition.
In addition to its technical uses, there are also extended uses, especially in non-scientific contexts, where it is used to mean defining characteristics or boundaries, as in the phrases 'test parameters' or 'game play parameters'.

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1. ### I Flat universe density parameter

For a flat universe, density parameter Ωuniverse=1. How does negative signage of a constituent density parameter, such as that of curvature index Ωk, which can be 0,1,-1 affect the signage of Ωuniverse? If Ωk were to be converted to its energy density, which is much less than the energy density...
2. ### A Putting upper bounds from a null result

Hello! If I have a measurement of a (dimensionless) parameter, ##a##, say 998 +/- 3 and the theoretical prediction of that parameter (assuming known physics) is 1000 +/- 4. Let's say that I want to set limits on a new parameter (not included in the theoretical calculations), call it ##\alpha##...
3. ### A Parameter optimization for the eignevalues of a matrix

Hello! I have a matrix (about 20 x 20), which corresponds to a given Hamiltonian. I would like to write an optimization code that matches the eigenvalues of this matrix to some experimentally measured energies. I wanted to use gradient descent, but that seems to not work in a straightforward...
4. ### I Density parameter and curvature index

For Ω=1, κ=0. Does the value of κ simply follow from the value of Ω, or can its value have an independent existence? So if Ω>1, does κ have to be 1?
5. ### I Solving an equation with a parameter and a derivative

idk how to start after finding the second derivative
6. ### I Differentiate w/ Respect to Affine Parameter: A Guide

Hi, there. I am doing differentiation with respect to an affine parameter ##s##, I am not sure whether my idea is right or wrong. Let ##C## be a geodesic for light and the path length ##s## on it be the affine parameter. Now I need to calculate ##\frac {\partial f}{\partial s}##, with ##f##...
7. ### A Lame parameter mu = shear modulus derivation (rogue factor of 2)

Hello, I am trying and failing to derive that the shear modulus ##G## is equal to the Lame parameter ##\mu##. I start with the linear, symmetric, isotropic stress-strain formula: $$\sigma = \lambda \mathrm{tr}(\epsilon) \mathrm{I} + 2\mu \epsilon$$ I then substitute a simple (symmetric) shear...
8. ### C/C++ Why should the copy constructor accept its parameter by reference in C++?

https://stackoverflow.com/questions/2685854/why-should-the-copy-constructor-accept-its-parameter-by-reference-in-c I've read these answers, but most of them aren't satisfactory. They just throw a big wall of text. I get they're trying to say something about infinite recursion, but I'm failing...
9. ### I Parameter Integration of Bubble Integral

Referring to this link : https://qcdloop.fnal.gov/bubg.pdf Using Mathematica Integrate command to solve it does not give the result stated here but I am unclear as to how they got to the result in the 4th line. It is clear that the integrand (1st line) can diverge for certain values of the...
10. ### I What are the units of the squeezing parameter?

As I understand it, when the squeezing operator acts on an annihilation/creation operator, a function of sinh(r) and cosh(r) is produced, where r is the squeezing parameter. I've been reading some papers that say that up to '15 dB of squeezing' have been produced in a laboratory. Does this mean...
11. ### I Hubble Parameter as function of time in universe models

This graph shows ##H## as a function of time related to the L-CDM model. Do we (@Jorrie) have similar graphs e.g. for ##\Lambda=0##; ##k=-1## critical, ##\Lambda=0##; ##k=0## open, ##\Lambda=0##; ##k=+1## closed? That would be great, thanks in advance.
12. ### Comp Sci Finding size of array passed as a parameter

#include<stdio.h> void sort(int arr[]){ int n=sizeof(arr)/sizeof(arr[0]); printf("%d",n);} void main(){ int array[]={12,11,54,6,77}; sort(array);} But I'm getting the answer as 2. I searched it up and found out that array has decayed into pointer and hence its showing size of pointer...
13. ### Mathematica Select[ list, condition] with a parameter in the condition

This works: a=0.4 Select[ list, #[[2]] > a-0.025 && #[[2]] < a+0.025 & ] {{401803.,0.42485,3.33299,0.776904,0.277985},{402066.,0.40333,9.23462,0.381478,0.397121},{402872.,0.41899,3.47237,0.742789,0.27385}} But why doesn't this work? :- Select[ list, #[[2]] > b - 0.025 && #[[2]] < b +...
14. 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 =...
15. ### I Conserved Quantity Along Affine Parameter

In the usual Schwarzschild coordinates the Lagrangian can be written: $$\mathcal{L}= \frac{\dot r^2}{1-\frac{2M}{r}} - \left( 1- \frac{2M}{r} \right) \dot t^2 + r^2 \dot \phi^2$$ where all derivatives are with respect to a (affine) parameter ##\lambda##, and where for convenience I have...
16. ### Mathematica Plotting a parameter Plane of a spring pendulum in Mathematica

I'm reading an article about the order-chaos-order sequence of a spring pendulum [Ref 1], as I'm reading it I'm trying to reproduce the graphs and results through Mathematica. However, I am new to this software. I will list below some of the most important equations mentioned in the paper. "In...
17. ### A Quantum weak measurement parameter estimation vs Classical Estimation

I am not an expert in quantum theory. I want to carry out some parameter estimation on a set of data I have. I have a model for the data with the parameter(s) of interest as variable(s). The data available is sporadic, meaning non-statistical or techniques involving no prior knowledge on the...
18. ### A Order parameter, symmetry breaking Landau style

Hi all, I am somewhat familiar the Landau Ginzburg paradigm for phase transition. My understanding is that it is a phenomological model of 2nd order phase transitions by "guessing" that the free energy can be expanded a configuration integral (path integral) of a functional of a local order...
19. ### I Is the Hubble constant a constant or is it a parameter?

(P.S! this is an open question, feel free to answer)
20. ### I Maximum impact parameter given effective potential

This problem is from David Morin's classical mechanics textbook: I am having trouble with Part b. Here is the textbook's answer: I do not understand why large particle energies lead to capture. I would think that smaller energies would lead to capture because the particle wouldn't have enough...
21. ### Storing device parameter data for a measurement system

We are working on new software for one of our measurement systems (written in Python). The new system is capable of measuring more devices simultaneously than before so keeping track of what we are doing is important; it will also be more automated. One of the things we want to implement is...
22. ### A Effects of a spatially nonuniform diffusion parameter

Einstein famously derived his relation between the diffusion constant of Brownian motion, particle mobility in a disippative medium, and temperature by considering Brownian motion in a harmonic oscillator potential. The result, $D = \mu k_BT$, is derived assuming that the mobility $\mu$ is...

34. ### I What Does a Negative Value for the Deceleration Parameter Imply in Cosmology?

I note the general Taylor series for ##a(t)## as: $$\begin{split} a(t)&\approx a(t_0) + a'(t_0) (t-t_0) + \frac{1}{2!} a''(t_0) (t-t_0)^2 ... \end{split}$$ which I rewrite as: \begin{split} a(t)&\approx a(t_0)\left(1 +...
35. ### A Regression: Regularization parameter 0

Hi guys, I am using ScikitLearn's Elastic Net implementation to perform regression on a data set where number of data points is larger than number of features. The routine uses crossvalidation to find the two hyperparameters: ElasticNetCV The elastic net minimizes ##\frac {1}{2N} ||y-Xw||^2 +...
36. ### Variations of a parameter in a differential equation

I tried to derive this by myself but I'm stuck. What i did it to substitute a_{1} with a_{1} +\Delta a_{1} in the first equation, getting: (a_{1}+\Delta a_{1})\dot{y}(t)+y(t)=b_{0}u(t)+b_{1}\dot{u}(t) and trying to subtract a_{1}\dot{y}(t)+y(t)=b_{0}u(t)+b_{1}\dot{u}(t) to it. But it's not...
37. ### Determine the range of a function using parameter differentiation

The strategy here would probably be to find a differential equation that ##f## satisfies, but differentiating with respect to ##x## using Leibniz rule yields ##f'=\int_x^{2x} (-te^{-t^2x}) \ dt + \frac{2e^{-4x^3}-e^{-x^3}}{x}## Continuing to differentiate will yield the integral term again...
38. ### Closest approach from initial velocity and impact parameter

Here were my assumptions: Energy and angular momentum are both conserved because the only force acting here is a central force. The initial angular momentum of this particle is ##L = mv_0b## and we can treat E as a constant in the homework equation given above. I solved for the KE (1/2 mv^2) in...
39. ### I New measurement of the Hubble Parameter

I just saw a new paper on measuring the Hubble Parameter : https://arxiv.org/pdf/1908.06060.pdf It seems they are agreeing with Planck which I understand would speak largely against the idea of new physics from the Hubble tension. However it says +14 and -7 next to the estimate. I presume...
40. ### I Equation of state and density parameter

Does ##w## = -1 by itself imply that spacetime is flat, or is it only due to ##\Omega##Matter + ##\Omega##Λ = 1 ?
41. ### Cosmology deceleration parameter

Homework Statement Homework Equations modified Freidmann: The Attempt at a Solution for part b) I am not sure what to do as I am not sure what they mean by and
42. ### I Gruneisen Parameter Ashcroft & Mermin Chapter 25: Exploring the Result

Ashcroft & Mermin Chapter 25, the Gruneisen Parameters are defined as: $$\gamma_{ks}=-\frac V {\omega_{ks}} \frac {\partial {\omega_{ks}}} {\partial V}$$ where the normal mode frequencies are defined by the eigenvalue equation: $$M \omega^2 \epsilon = D(k) \epsilon$$ The volume of the crystal...
43. ### Problem understanding a parameter in a digital filter

Homework Statement Digital causal recursive filter is a part of a digital signal processing system which has sampling frequency ##fs = 1200Hz## and is given by a differece equation: where ##r = 0.9## and ##θ## is such that it filters out the spectral components at ##f = 200Hz## Find ##H(z)##...
44. ### I What is the Hubble Parameter over time and how can I calculate it?

How can I calculate the Hubble Parameter in time. I know that it decreases in time and approaches to some constant value but I am not sure to what value, Is there any graph for that ?
45. ### A Exploring parameter space of inflation models

I have been studying primordial black hole formation through inflation for a while and I was curious to know how the parameters in an inflation model are determined such that they are consistent with CMB constraints. In my literature reviews, there are quite a few models that exhibit an...
46. ### A Lattice parameter difference: PBE vs PBE-D3 functional

Hi guys! Does anyone know why the lattice parameters of a crystal calculated with PBE-D3 functional are lower than those calculated with PBE? Thanks in advance! :)
47. ### A What is the key parameter in fusion: momentum or energy?

The released products of a transmutation reaction (I say transmutation when 2 particles reacts to generate more than one) follows the conservation of kinetic energy law. Also particles moving in opposite direction can have equal speed one with respect the other than rather if one of them is...
48. ### I Eliminating the Parameter from Helix Equation

Let's say you have a helix defined parametrically as r(t) =<sin(t), cos(t), t> Is it possible to eliminate t and write an equation for this helix just in terms of x, y, and z?
49. ### B Is Bell's parameter really a hidden variable ?

In the Ansatz : $$C(a,b)=\int A(a,s)B(b,s)ds$$, is $$s$$ not simply the mute summation index ? In this sense it is not hidden to the experiment. Then what about an "dummy" hidden variable that is not integrated over : $$C(a,b)(\phi)=\int A(a,s,\phi)B(b,s,\phi)ds$$ $$\phi$$ were tuned one and...