Questions tagged [numerical-value]
Question relating numerical representations, operations and methods, including approximate results instead of exact symbolic results.
1
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2answers
94 views
Solving BPV of second order nonlinear ODE through NDSolve
I'm trying to solve a 2nd order related ODE system in two region using Piecewise. BC: 1) y'[0]=0 and at y'[1.6]=0 while at 1 <...
1
vote
1answer
65 views
Finding the value which gives a list total of zero
Is there a way to check if x will converge for Total[g] approaching zero in this code example? For n=15000000, 1.87 < x < 1.88, but takes awhile to run. Thanks.
cheers,
Jamie
...
1
vote
1answer
33 views
Numerically approximating the series of the solution to a PDE
Suppose I had a PDE such as the heat equation in two variables, and I want to solve it with mathematica, and ask it to return me a series expansion of the solution. For example,
...
0
votes
1answer
52 views
How to find all numerical roots in exponential equation? [closed]
I have this function:
d = 7.61;
beta = 0.0193;
lnot = 74.1;
morse[x_] := d*(1 - Exp[-beta*(x - lnot)])^2;
and I can see there are 2 roots because when I do
<...
1
vote
0answers
39 views
Exponential distribution and numerical errors?
I am working on the measure of a Curie Weiss model over a lattice
$$
\mu[m] = \frac{e^{\beta N (hm + m^2)}}{\sum_z e^{\beta N (hz + z^2)}}\binom{N}{\frac{(1-m)N}{2}}2^{-N}
$$
where $m\in\{-1,-1+2/N,\...
2
votes
1answer
50 views
How do I make InverseBetaRegularized function behave the same in Mathematica 11.3 compared to 11.2?
In Mathematica 11.3:
InverseBetaRegularized[0.001, 4501, 500]
Never finishes calculating.
...
3
votes
2answers
162 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
24 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
66 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
39 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
90 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
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2answers
103 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
87 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
38 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
59 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
289 views
1
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2answers
75 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
29 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
159 views
Mathematica and IBVP mixing temporal and spatial derivatives
The following PDE's-system-solving code
...
0
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1answer
60 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
48 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
46 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
261 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
58 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
200 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
127 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
90 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
109 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
56 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
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0answers
38 views
Finding zero linear combinations of polynomials (numerically)
I have two functions of real variables defined on two compact spaces
...
0
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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
85 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
56 views
Numerical solution of a system of two exponential equations
I need to solve this two equations for x and y:
...
1
vote
2answers
70 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
52 views
0
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2answers
69 views
equal expressions give different numerical result
I have two expressions, and they are really equal:
...
0
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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
167 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
109 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
51 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
77 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
126 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
113 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
100 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
72 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
66 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 ...
