Questions tagged [numerical-value]
Question relating numerical representations, operations and methods, including approximate results instead of exact symbolic results.
3
votes
2answers
135 views
NIntegrate on a solution of a matrix ODE
I've seen similar questions on this site but somehow the solutions there didn't manage to solve my specific problem.
I have a function mat1 that takes a square $n \times n$ matrix G, and some final ...
1
vote
0answers
23 views
Getting values of EllipticK with arguments that are very near 1
I need to evaluate EllipticK[m] very close to 1. However, when I get too close to 1 the function defaults to the exact solution for 1 , which is ...
0
votes
0answers
59 views
Clebsch Gordan coefficients
I'm trying to compute various sums which contain some CG coefficients, where the sum runs over the indexes m1,m2,m corresponding to each of the three angular momenta j1,j2,j. The thing is that when I ...
0
votes
1answer
36 views
0
votes
1answer
30 views
NDSolve::dsvar error when trying to solve system of differentail equations
I'm currently trying to solve a set of differential equations using NDSolve but I'm getting an error... The following was construced with the help of this answer ...
1
vote
1answer
87 views
Conditional evaluation: black hole cross section
I'm trying to calculate the collision cross section of black holes, more precisely, I want the critical impact parameter $b_{\text{crit}}$ for a given initial velocity $v$ such that, at this speed, ...
1
vote
2answers
84 views
Can one define 0 Log[0] = 0?
With reference to this post, can one define 0 Log[0] = 0 in Mathemtica?
3
votes
1answer
86 views
Comparing exact expressions vs real numbers
Often I need to generate some data using some symmetry operations and I usually keep them as exact expressions (for example, consider the points on a triangular grid ...
2
votes
1answer
37 views
Computing the Multivariate Normal density gives sometimes different values from in-built function
I'm trying to define the density of the Multivariate Normal distribution, since it will be faster to compute for greater dimensions (vectors of size 50 or more), specially when I have to do those ...
2
votes
1answer
55 views
Strange plot artifacts when plotting the underdamped oscialltor solution
I'm plotting something trivial; the solution to an underdamped harmonic oscilator:
$$x(t) = A_{0} \cos(\omega t) e^{-t/\tau}$$
In MM speak I say:
...
2
votes
3answers
288 views
1
vote
2answers
63 views
Having problems with using TableForm to format a table
I want to make a table of various values of the logistic curve given by l[x_] := 1/(1 + E^((-k)*(x - \[Alpha]))).
In basic form, this is dead easy. However, I want ...
0
votes
1answer
27 views
Fitting a numerical function with another function that depends on parameters
I'd like to fit a branch of the Lambert function :
-ProductLog[-1, x]
in the interval $[-0.35,0]$ with a function of the form $-a\log(-bx)+c+d x$ or $-a\log(-x)+...
3
votes
1answer
148 views
Mathematica and IBVP mixing temporal and spatial derivatives
The following PDE's-system-solving code
...
0
votes
1answer
57 views
Increasing MaxExtraPrecision arbitrarily changes numerical result
I am trying to confirm that a function $f$ satisfies a particular differential equation of the type $D f=0$, for some differential operator $D$. I set $Df$ as Diffeq...
0
votes
1answer
42 views
How to extract the minimal value from NMinimize? [closed]
According to the manual, if I calculate
NMinimize[x^4 - 3 x^2 - x, x]
that returns {-3.51391, {x -> 1.30084}}, I can extract the minimal value -3.51391 using
<...
0
votes
0answers
45 views
High numerical precision failing [duplicate]
N[(1 - 2*6.674*6*10^13/(6371000*299792458^2))^(0.5), 20]
1.
What I expect:
...
8
votes
5answers
253 views
Functional fixed points (ie fixed point of mapping from function space C[0,1] to itself)
I am looking for some tips or guidance as to what machinery in mathematica can help me get at this problem numerically. I am looking for fixed points of a mapping, but the objects in question are ...
1
vote
2answers
55 views
Numerics & List Manipulation:ListCorrelate: yield $\{-f1 + f2, \dots, -f2 + f4, \dots\}$ from $\{f1, f2, f3, f4, f5\}$
The command
ListCorrelate[{-1, 1}, {f1, f2, f3, f4, f5}]
yields
{-f1 + f2, -f2 + f3, -f3 + f4, -f4 + f5}
is there any simple way to get
{-f1 + f2, -f1 + ...
2
votes
2answers
198 views
Help for Solving Two Equations For Two Unknows (from a Paper)
I am trying to reproduce numerically the results found in this paper: https://ieeexplore.ieee.org/document/1707778
You don't necessarily need to read it. Basically I boils down to solving a two ...
0
votes
4answers
126 views
How to solve equation in integer numbers
I would like to solve an equation like this $\frac{\log(2)}{\log(3)}=\frac{n-0.5}{k-0.5}$ where $n$, $k$ are positive integers and $\log$ is natural logarithm. Of course, I can do only numerical ...
1
vote
2answers
106 views
Sampling data from numerical values of density distribution of nucleons
How could i sample my data which follows distribution if i have only numerical values of density distribution as an example data attached as in picture
I tried but do not know how to do it.
The data:...
0
votes
3answers
32 views
Low precision from function returning matrix
Got a function depending on single parameter "t" defined below which
returns a 2 by 2 matrix
...
1
vote
1answer
87 views
Second-order nonlinear boundary value problem
I am trying to follow this work, in which Eq. (11), the 2nd-order, nonlinear differential equation depends on a pair of parameters $ (\kappa, h) $. But now I only care about the case with a vanishing $...
3
votes
1answer
106 views
Solve a system of 4-th order polynomial equations (numerically)
I have a function defined on $ S^6 \times S^6 $ (two spheres embedded in $ \mathbb{R}^7 $ individually). Let us call this vector $ \vec{f}(\vec{x},\vec{y}) $, where $ \vec{x} $ and $ \vec{y} $ are ...
3
votes
1answer
53 views
Numerical precision problem
I have this simple code:
ep = 1 - 80000000000 (-(199999/200000) + 1/E^(1/200000))
ep // N
-8.27404*10^-8
...
1
vote
0answers
38 views
Finding zero linear combinations of polynomials (numerically)
I have two functions of real variables defined on two compact spaces
...
0
votes
1answer
31 views
Best practice when encountering “Indeterminate” when applying a value equal to infinity
I have the following equation, which equals 1 for positive values of $n$, but at $n = \inf$ the equation becomes indeterminate.
4 n (1 - 1/2) 1/2 (1/Sqrt[n])^2
...
3
votes
1answer
79 views
Why does NSolve give different results in different version of Mathematica?
I am working on a problem with a colleague who uses Mathematica v.10.2 while I have v.11.0 Student Edition. We are solving the exact same equations but get two slightly different results. Why would ...
2
votes
1answer
55 views
Numerical solution of a system of two exponential equations
I need to solve this two equations for x and y:
...
1
vote
2answers
67 views
Solving a system of equations with numerical approximation [closed]
Let a, b, c be vectors obtained with the function N and x, y be scalars. I have the equation:...
-1
votes
1answer
50 views
0
votes
2answers
66 views
equal expressions give different numerical result
I have two expressions, and they are really equal:
...
0
votes
0answers
22 views
Raising a negative number to a fractional power, why the result is different? [duplicate]
In the math theory, we know have
$$(x)^{\frac{m}{n}=}\sqrt[n]{x^m} \ ,$$
it means
$$(-1.5)^{\frac{1}{0.3}}=(-1.5)^{\frac{10}{3}}=\sqrt[3]{(-1.5)^{10}}=\sqrt[3]{1.5^{10}}\simeq 3.8634 \ .$$
But in ...
3
votes
0answers
159 views
On Ж, and the fine-structure constant
I'm trying to reproduce the results from a certain infamous paper that has been moving around the web for the last few days. The details are irrelevant.
This paper claims to have a closed-form ...
0
votes
2answers
106 views
Product of large number with a very small number returns zero because Mathematica sets the very small number equal to zero [closed]
I have a product Exp[-I*Pi*x]*BesselK[-1, 2.43*Ix]. Now, Exp[-I*Pi*x] grows larger and larger as $x$ increases for imaginary ...
2
votes
0answers
47 views
What is the acceptable error in numerical calculations? [closed]
I am doing a calculation where I try to simplify a very complicated complex function. I did this step by step and I checked that the numerical values that the function gets for certain values of the ...
0
votes
1answer
73 views
Taylor Series of numerical solution of FindRoot
I have found the inverse to the following equation by using FindRoot. I want to have a Taylor approximation (say starting from ...
6
votes
4answers
124 views
Suppress trailing 0s in numerical values
For example, this is what I want
In[1]:= N[Table[4^(i/4), {i, 1, 4}]]
Out[1]= {1.41421, 2., 2.82843, 4.}
But if I want a few more digits only from the irrational ...
3
votes
0answers
47 views
Is there a function that returns me the largest common divisor? [closed]
Is there a function that returns me the largest common divisor?
I tried this:
Intersection[Divisors[200], Divisors[280]] // Last
0
votes
1answer
109 views
How to test if a solution of NDSolve is positive
I want to solve a differential equation numerically and determine one of the parameters in the D.E. The goal is to determine $M$ such that the function goes asymptotically to zero or to put it in a ...
0
votes
2answers
94 views
Computing a sum with high precision
I am aware that a similar question has been asked, for example, here and here, but none of the proposed solutions solves my problem, so please wait before you mark this question as a duplicate.
...
1
vote
1answer
70 views
How do I to remove a factor of 1 [duplicate]
I evaluated
Subscript[ε, 1, 2] = 0.5 Subscript[γ, 1, 2]
2 μ Subscript[ε, 1, 2]
1. μ Subscript[γ, 1, 2]
How do I to remove ...
1
vote
1answer
64 views
How to make Mathematica show small and large results? [closed]
I have two equations with x=r+Log[-1+r] and v=(1-1/r)/r^3 forms. When I substitute ...
1
vote
0answers
36 views
Getting the coordinates of a specific point out of a plot [closed]
I have the following piece of code that in the first part calculates and plots a function and it uses it in the second part to perform an NDSolve. After that I am plotting two functions. What I would ...
0
votes
0answers
52 views
Fastest way to find roots and reproduce this result
I am trying to solve the following transcendental equation numerically with the given values and to reproduce the diagram attached below.
$0=\frac h2\sqrt{\left(\frac{\omega\cdot n_1}c\right)^2-\...
3
votes
1answer
115 views
How to avoid rounding error, when exporting numerical values
How to avoid the rounding error, when exporting data like this:
ra = Range[0.004, 0.074, 0.0005];
Export["range.txt", ra]
The result is this:
2
votes
0answers
90 views
How solve this equation and plot the results?
I want to solve the following function and get values for $\omega$.
$$\omega - \omega_{21} + i/\tau_{2} - s_{1}\alpha_{1}(\omega)[1+f(\omega)] = 0$$
The function $f(\omega)$ is the troublesome ...
1
vote
1answer
41 views
Numerical solution to integration of function which parameters define the integral limits
I have following equation:
$\int^{\delta_c}_{\delta_c-\pi}\sqrt{h^2_c(\cos(\delta_c)^2-\cos(\delta)^2+\Omega_c(\delta_c-\delta)}\text{d}\delta=\pi$,
where $\delta_c=\frac{1}{2}\arcsin\left(\frac{\...
2
votes
1answer
76 views
Numerical artifacts appearing ONLY on boundary of 3Dplots and not on Plot
I have a behavior with 3D plots I really don't understand and I would like to correct it.
I have a 2D function to plot, here is its graph with Plot3D :
We can see that on the top boundary of $\Delta ...
