Function Definition and 1000 Threads

In mathematics, a function is a binary relation between two sets that associates to each element of the first set exactly one element of the second set. Typical examples are functions from integers to integers, or from the real numbers to real numbers.
Functions were originally the idealization of how a varying quantity depends on another quantity. For example, the position of a planet is a function of time. Historically, the concept was elaborated with the infinitesimal calculus at the end of the 17th century, and, until the 19th century, the functions that were considered were differentiable (that is, they had a high degree of regularity). The concept of a function was formalized at the end of the 19th century in terms of set theory, and this greatly enlarged the domains of application of the concept.
A function is a process or a relation that associates each element x of a set X, the domain of the function, to a single element y of another set Y (possibly the same set), the codomain of the function. It is customarily denoted by letters such as f, g and h.If the function is called f, this relation is denoted by y = f (x) (which reads "f of x"), where the element x is the argument or input of the function, and y is the value of the function, the output, or the image of x by f. The symbol that is used for representing the input is the variable of the function (e.g., f is a function of the variable x).A function is uniquely represented by the set of all pairs (x, f (x)), called the graph of the function. When the domain and the codomain are sets of real numbers, each such pair may be thought of as the Cartesian coordinates of a point in the plane. The set of these points is called the graph of the function; it is a popular means of illustrating the function.
Functions are widely used in science, and in most fields of mathematics. It has been said that functions are "the central objects of investigation" in most fields of mathematics.

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  1. V

    Creating a Double Precision Matlab Function from Scratch

    I am confused at how to code this without using any of matlab's already built in functions except for using double. Is this question just asking me to write out the function and then make sure it's double precision?
  2. H

    Improper integral of a normal function

    I'm trying to solve an improper integral, but I'm not familiar with this kind of integral. ##\int_{-\infty}^{\infty} (xa^3 e^{-x^2} + ab e^{-x^2}) dx## a and b are both constants. From what I found ##\int_{-\infty}^{\infty} d e^{-u^2} dx = \sqrt{\pi}##, where d is a constant and...
  3. T

    What is the origin and validity of assumptions about the strain energy function?

    Earlier today, I posted a question about the strain energy function. I am happy with the answer (I love this group). But the answer opened up a deeper question. Many elasticity textbook posit the existence of a strain energy function: And they make an additional assumption about its...
  4. H

    Calculating total derivative of multivariable function

    This isn't a homework problem exactly but my attempt to derive a result given in a textbook for myself. Below is my attempt at a solution, typed up elsewhere with nice formatting so didn't want to redo it all. Direct image link here. Would greatly appreciate if anyone has any pointers.
  5. H

    Finding roots: cosine function of x

    I need to find the zeros of this function where d,L,v are constants. After several calculations I faced this equation. I tried everything I know, but I can't solve this. Maybe I'm missing something or I must made a mistake earlier in the problem. Thus, I would like to know if it is possible to...
  6. chwala

    Solve the problem involving probability density function

    This is the question: This is the ms solution- from Further Maths paper. My question is referenced to the highlighted part. I can see they substituted for the lower limit i.e ##x=1## to get: ##F(x)=\dfrac{x^3-1}{63}## supposing our limits were; ##2≤x≤4## would the same approach apply? Anything...
  7. A

    Engineering How do radial tooth clutches function?

    Greetings I have a hard time understanding how the radial tooth clutch function when it stops transferring power . Basically I understand that clutches: 1) transfer power from input shaft to output shaft 3) disengage when the torque transmitted has reached a certain limit ( normally when the...
  8. chwala

    Solve the given equation using the Lambert W function

    I just came across this...the beginning steps are pretty easy to follow...i need help on the highlighted part as indicated below; From my own understanding, allow me to create my own question for insight purposes... let us have; ##7^x=5x+5## ##\dfrac{1}{5}=(x+1)7^{-x}##...
  9. cnh1995

    Engineering What is wrong in this 2nd order transfer function?

    I have attached my attempt at a solution. In the solution image, I have computed 3 things: 1. System transfer function based on my understanding of the problem statement. This is a 2nd order system with steady state dc gain=0.9. So I wrote the transfer function accordingly. However, I strongly...
  10. topsquark

    LaTeX Commutative function diagrams in LaTeX

    I know that TikZ is probably the best way to do this but most Forums don't use it. I can make a rectangular diagram, but it's a bit clunky: Say I have the commutative function diagram: ##\begin{array}{ccccc} ~ & ~ & f & ~ & ~ \\ ~ & A & \longrightarrow & B & ~ \\ g & \downarrow & ~ &...
  11. J

    Using Gauss's Law to Calculate Charge Density Function

    I've attached what I have so far. Used Gauss's law, everything seemed to make sense except the units don't work out in the end. The charge density function if given by: r(z)=az, where z is the perpendicular distance inside the plane.
  12. besebenomo

    Magnetic flux of magnetic field changing as a function of time

    $$B(t) = B_{0} \frac{t^2}{T^2}$$ for ##0 \leq t \leq T## The issue here is more conceptual, because once I find the flux of B I know how to proceed to find the current. I got velocity (but it seems to me that it is the initial velocity), I could use it to find the time in function of space...
  13. Ennio

    B Sinusoidal wave function of t and x

    Greetings, is it possible to characterize a sinusoidal wave in the domain of time and then pass into the domain of movement along x direction? I start with: a is the amplitude of the sine function and ω is the angular velocity. t is the time. I can express the angular velocity in funct. of the...
  14. M

    Python Any help with this error in Scipy minimize function?

    Hi PF! When I execute the code below: import numpy as np from scipy.stats import t import scipy.optimize as optimizeglobal data data = np.random.normal(loc=50, scale=1, size=(2400, 1)).flatten() def L(F): M = 250 lmda = 0.97 sig_0 = F[0] for i in range(1, 12): sig_0 +=...
  15. Ennio

    A Calculate the exact or approximate length of one period of the wave function

    The known expression of the wave function is where A is the amplitude, k the wave number and ω the angular velocity. The mathematical definition of arc length for a generical function in an interval [a,b] is where, in our sinusoidal case: For our purpose (calculation of the length in one...
  16. M

    Python Scipy minimizer function and function executions

    Hi PF I'm trying to minimize a function func via scypi's minimiz function, as shown below. import numpy as np import scipy.optimize as optimize def func(x): y = x[0]**2 + (x[1]-5)**2 print('hi') return y bnds = [(1, None), (-0.5, 4)] result = optimize.minimize(func, method='TNC'...
  17. The Bill

    I Name of distance to nearest multiple of n function?

    I've defined this function to clean up some pages of work I've been doing on relations of integers modulo n. Let's call it mav(a,n) for now. mav(a,n) for integers a and n is equal to the Euclidean distance from a to the nearest multiple of n. To compute it in programming languages I've been...
  18. J

    What is aerodynamics function of front active lip spoiler?

    This is question for aerodynamicist, so I put it here in aerospace department. (Mechanical engineers don't learn aerodynamics at university) What is aerodynamic function of active front lip spoiler (on video) and what is function of flexibile plate infront of front tyers(picture)? Why reduce...
  19. jjson775

    I Understanding Wave Function Probabilities for a Free Particle

    The textbook I am self studying says that the wave function for a free particle with a known momentum, on the x axis, can be given as Asin(kx) and that the particle has an equal probability of being at any point along the x axis. I understand the square of the wave function to be the probability...
  20. ergospherical

    I 4D d'Alembert Green's function for linearised metric

    Q. Calculate the linearised metric of a spherically symmetric body ##\epsilon M## at the origin. The energy momentum tensor is ##T_{ab} = \epsilon M \delta(\mathbf{r}) u_a u_b##. In the harmonic (de Donder) gauge ##\square \bar{h}_{ab} = -16\pi G \epsilon^{-1} T_{ab}## (proved in previous...
  21. yklee

    Ising model autocorrelation function calculation

    Dear Mr. and Ms., I am trying to measure the autocorrelation functions of 2D ising model based on the equation given by where A(t) denote a measure. I calculate a c(t) of magnetization. I calculated in this way data_path = f"../../trajectory/data.txt" data = np.loadtxt(data_path)...
  22. S

    Mathematica Function that integrates another function, with units

    Velocity as a function of time, defined with units attached (Quantity feature of Mathematica): fnVq[t_ ]:= 2 m/s^2 * t fnVq[5 s] Integrate[fnVq[tt],{tt,0 s, 2000 ms}] 10m/s 4m When we printed above the value and integral, we got the correct results with proper units. Now I'm trying to...
  23. patric44

    Is f(z) =(1+z)/(1-z) a real function?

    hi guys i found this problem in a set of lecture notes I have in complex analysis, is the following function real: $$ f(z)=\frac{1+z}{1-z}\;\;, z=x+iy $$ simple enough we get $$ f=\frac{1+x+iy}{1-x-iy}= $$ after multiplying by the complex conjugate of the denominator and simplification $$...
  24. MevsEinstein

    I Defining the Prime Gap function

    Hi PF! I created a function ##R(x)## that gives the gap between the largest two primes less than or equal to ##x##. To define it, I used this property: $$\pi(x+R(x))=\pi(x)+1$$ Which is true since the ##x## distance between ##\pi(x)## and ##\pi(x)+1## is ##R(x)##. If we solve for ##R(x)## we...
  25. H

    I Partition function for continuous spectrum

    Let's say that we have a one-particle Hamiltonian that admits only a continuous spectrum of eigenvalues ##E(k)=\alpha k^2## parameterized by asymptotic momentum ##\mathbf{k}## (assuming the eigenfunctions become planewaves far from the origin), would the partition function then be $$Z=\int...
  26. Aethermimicus

    I What is the function of the air cavity inside drums?

    I'm trying to understand the function of the air cavity inside drums. I've read that 'The air cavity inside the drum will have a set of resonance frequencies determined by its shape and size. This will emphasize some frequencies at the expense of others.' Then what are the resonance...
  27. MevsEinstein

    B Particle Function? Particle Equation?

    The following is the wave equation from Electrodynamics: $$\frac{\partial^2 \Psi}{\partial t^2} = c^2\frac{\partial^2 \Psi}{\partial x^2}$$ Where ##\Psi## is the wave function. But because of Heisenberg's Uncertainty, physicists had to come up with another equation (the Schrodinger equation)...
  28. Keysa

    How to find the positive maximum value of a function

    This is the code that i wrote Clear["Global`*"] Z = 500; W = 100000; G = 250; H = 100; K = 0.5; T = 30; L = 4000; P = 5; S = 2.5; Y = 1; A = 0.1; V = 2.5; J = 8000; f[x_] := 1/ x {(J*Z*x*(2*Y - x))/( 2*Y) - ((W + T*G) + ((L + T*P)*2*Z*Y*(1 - ((Y - x)/Y)^1.5))/ 3 + (H + T*S +...
  29. junyoung

    I Open interval or Closed interval in defining convex function

    The Korean textbook standard defines the convexity of the function as an open section. Many textbooks and university calculus textbooks define the convexity of the curve as an open section. However, some textbooks define convexity as closed sections. Do you think it is right to define the...
  30. mcconnellmelany

    Find dissipative function for the non-linear force f=-bv^n

    For a nonconservative force, What would be the dissipative function for a force f=-bvⁿ in Lagrangian (Where v is the velocity) [#qoute for a nonconservative force f=-bv The dissipative function is D=-(1/2)bv² ] Since ##f=\frac{\partial D}{\partial \dot x}## so the dissipative function should...
  31. Tesla In Person

    Thermodynamic Cycle -- Work done as a function of Heat absorbed

    During a thermodynamic cycle, an ideal thermal machine absorbs heat Q2 > 0 from a hot source and uses it to perform Work W > 0, giving a cold source a heat Q1 < 0 with an efficiency of 20% . How much is the work done as a function of Q1 ?I have 2 question regarding this problem: 1) Why is Q1 the...
  32. T

    I Converting Second Order ODE to Hypergeometric Function

    I believe it is the case that any linear second order ode with at most 3 regular singular points can be transformed into a hypergeometric function. I am trying to solve the following equation for a(x): where E, m, v, k_{y} are all constants and I believe turning it into hypergeometric form will...
  33. StoneBored

    How to get the transfer function for force transmissibility of a wall?

    Hi, I am trying to get the transfer function from a wall between rooms. From one side I have the force of a hammer as an input ,and in the other side of the wall (next room) I have an accelerometer. Is it possible to get the TF without know the damping, stiffness and mass of the wall partition...
  34. Eclair_de_XII

    Fortran Does Fortran have a built-in function to calculate the determinant?

    program main ! use ! some library that defines the function to calculate the determinant of a given matrix implicit none real,dimension(2,2)::A real::det_val A(1,1)=1 A(2,2)=1 A(2,1)=0 A(1,2)=0 ! det_val=det(A) print *,det_val ! Should print 1. end program main
  35. justpeeking

    B How does a spinor affect a wave function?

    How do spinors affect wave function solutions? Like how is the output different
  36. A

    Engineering Is it possible for a low pass filter to have such a transfer function?

    Hello! Consider this filter,and that I have to find the transfer function U2/U1 with the norm Ω= ωRC (also double fractions are not allowed) Now I can see that that the resistor and capacitor left as well as right are parallel to each other. So simplifying that ## Z_1 = \frac{R}{jωRC +1}...
  37. WMDhamnekar

    MHB Math Help: Understand How to Compute $F_{X_1}(x)$

    Now, I don't understand how did author compute $F_{X_1}(x) = \displaystyle\sum_{j=1}^n \binom{n}{1} F^1(x) (1-F(x))^{n-1} = 1-(1-F(x))^n ?$ (I know L.H.S = R.H.S) Would any member of Math help board explain me that? Any math help will be accepted.
  38. WMDhamnekar

    A Derivation of P.D.F. from distribution function

    Author computed ##f_{X_k}(x)## as follows but I don't understand it. Would any member explain me the following computations?
  39. D

    If f(x)=(e^x+e^-x)/2, what is the inverse function?

    Hi everyone This is the solution for the problem. I don't understand how they got from To This was my attempt at a solution I can't seem to get rid of one of the y terms and am left with one on each side. Could someone explain the solution to me please? Thanks
  40. MevsEinstein

    B What function satisfies this table?

    I have a table of values (from my own analysis, not from a textbook) that represents a portion of a periodic function: x y 0 30 1 20 2 10 3 10 4 20 5 30 What function satisfies the table? What I know is that the function is periodic. I was thinking I could use cosine because its...
  41. Tertius

    I Co-Moving Coordinates & Lapse Function N(t) in ADM Decomposition

    In the ADM decomposition, like in the construction of the FRW metric, the coordinates are defined to be co-moving, so we know $$d\tau = dt$$ (i.e. the lapse function is normalized away) Starting from a five-dimensional embedded hyperboloid (as in carroll pg. 324) ## -u^2 + x^2 + y^2 + z^2 + w^2...
  42. C

    I Acceleration as a Function of Time Using Constant Power

    Hello everyone! I was doing some dimensional analysis to find an equation that gives a acceleration as a function of time, using constant power. I came up with the equation $$a = k\sqrt {\frac P {mt}}$$ I differentiated velocity with respect to time in order to check my work and also checked out...
  43. Simobartz

    I Hamiltonian formalism and partition function

    In hamiltonian formalism we have the generalized coordinates ##q_i## and the conjugates moments ##p_i##. For a dipole in a give magnetic field ##B## the Hamiltonian is ##H=-\mu B cos \theta## where ##\theta## is the angle between ##\vec \mu## and ##\vec B##. Can i consider ##\theta## or ##cos...
  44. A

    Engineering How do I draw the Bode diagram of this transfer function?

    Hello! I have this filter here a) Calculate the transfer function T(Ω) = Ua/Ue using voltage dividers.For this, use the normalized angular frequency Ω = ωRC and bring the result into the form ##T(Ω) = \frac{A+jB}{C+jD} ## . The result must not contain any double fractions. I was able to that...
  45. P

    A Symmetry of the Green-Keldysh-Nambu function

    Hello, I would like to understand a relation of this article by Volkov (eq. 4). Let's define the Green function $$ G^{ij}_{ab} (1,2) = -i \langle T_c \Psi_a (1_i) \Psi_b (2_j) \rangle $$ where ##a,b = (1,2)## are the spin indices and ##i,j = (1,2) ## are the indices for the Keldysh contour ...
  46. M

    Python Python - Endpoint : Can the function not return an array of dictionaries ?

    Hey! 😊 I am trying to write a code for a server in Python and I got stuck. I gave as an input a csv file and using pandas we get a dictionary where the titles are the keys and the inputs are the values. From that we get the below : I have written the below endpoint to get all the...
  47. S

    I How Does Electron Spin Affect the Partition Function in Saha's Equation?

    Hey, I have a question about proving Saha's equation for ionizing hydrogen atoms. The formula is \frac{P_{p}}{P_{H}} = \frac{k_{B} T}{P_{e}} \left(\frac{2\pi m_{e} k_{B}T}{h^2} \right)^{\frac{3}{2}}e^{\frac{-I}{k_{B} T}} with P_{p} pressure proton's, P_{H} pressure hydrogen atoms, m_{e}...
  48. M

    Partition Function for system with 3 energy levels

    I determined the partition function of the particle A, B and C. C should be the same as B. I then considered the situation, where all particles are in the system at the same time, and drew a diagram of all possible arrangements: The grey boxes are the different partitions, given that we...
  49. V

    Finding tension as a function of distance from the center of rotation

    I'm not too sure how to account for both the mass and the rope at once. I think the following are true for the two individually: For the mass at the end, ## T = m ω^2 L ##, following from ##a = v^2/r##and ##v=ωr##. For the rope, ##dT = ω^2 r dM##, where ##dM = λ dr## and λ is the mass per unit...
  50. LCSphysicist

    Finding the generator function for 4 variables

    Prove directly that the transformation $$Q_{1} = q_{1}, P_{1} = p_{1} − 2p_{2}$$ $$Q_{2} = p_{2}, P_{2} = −2q_{1} − q_{2}$$ is canonical and find a generating functionSo the first part is easy and can be skipped here. I have some difficults regarding the second part, namely, the one that ask for...
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