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Questions tagged [numerical-value]

Question relating numerical representations, operations and methods, including approximate results instead of exact symbolic results.

3
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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
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1answer
36 views

Reverse the reccurence mirrorwise

Let be a recurrence for polynomials $R_{m,j}$ ...
0
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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
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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
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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
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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
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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
0
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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
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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
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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
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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
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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
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
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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:...
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1answer
50 views
0
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2answers
66 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
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 ...