Questions tagged [numerical-value]
Question relating numerical representations, operations and methods, including approximate results instead of exact symbolic results.
174
questions
0
votes
0answers
34 views
Explain difference in Floor[Log[10., 1000]] and Floor[Log[10, 1000]] [closed]
I executed the following function:
Floor[Log[10., 1000]]
I expected as result:
3
but the result was
...
1
vote
1answer
59 views
Problem with Solve and PrimeZetaP
I assume this is something to do with limits on numerical precision, but can someone explain the difference in output between these two Solve problems:
...
6
votes
1answer
84 views
Using Around with NDSolve
I was trying to obtain the same result of a differential equation with to different methods the first one is based on DSolve and the second one is based on NDSolve
...
1
vote
2answers
53 views
MemberQ giving false when the answer is true? [duplicate]
Lets generate a large grid
grid=Table[{i,j},{i,0,10,.01},{j,0,10,.01}]
MemberQ[grid,{7.02,.02}]
The above MemberQ gives me False. (even though it must be true ...
2
votes
1answer
182 views
0
votes
0answers
99 views
Using NDSolve for differential equations
I'm trying to numerically solve the following differential equations eqs for plotting the bifurcation diagram. However, under special values of the parameter u, I get a problem when calculating the ...
3
votes
1answer
72 views
Proving the positive semidefiniteness of a 6X6 symbolic matrix
Specifically, I want to check the positive semidefiniteness of the following 6X6 symbolic matrix
...
0
votes
1answer
141 views
Evaluate and Plot x=x+1
I have a function of the form x=x+dx, whereas x(z) and dx(x,z) both depend on a increasing integer. Now I would like to evaluate this function after n time steps. In addition to that I'd like to plot ...
0
votes
1answer
68 views
Is this false solution? [closed]
I tried W.A to find the solution for $log(-i)$ and the result is $log(-i) = -i\pi/2$ . But I calculate 'by hand' that $e^{-i\pi/2} = i ?$ . Is this result / solution false ?
0
votes
1answer
47 views
Derivative does not correspond to function
I have an implicitly defined function, f[p], and I plot it together with its derivative. As is clear from the picture, the function is increasing, but the ...
2
votes
1answer
82 views
Laplace equation DirichletCondition ignored
My goal is to find out force between two parallel identical disks with Voltage difference.
To solve this, I tried to use laplace equation.
And below is my code.
where R is radius of disks, d is ...
3
votes
2answers
70 views
Checking NDEigensystem Results
I'm looking to verify the output of a call to NDEigensystem. I'm doing this by plotting the operator acting on the Interpolating Function outputs versus the ...
2
votes
2answers
241 views
Simplify appears to give different results
I have an issue with Simplify (and FullSimplify) giving a different numerical expression to the pre-Simplified expression. The function is an alternating sum of trigonometric quantities:
...
1
vote
0answers
37 views
What is used for the % symbol in mathematica? [duplicate]
Im new in mathematica i want to know logic about this program. I got this code:
{{vo, vn, Ii}} = {vo, vn, Ii} /. %;
i know that the syntax /. is for replacement but i dont know whats going on with ...
0
votes
1answer
25 views
Equation solving for approximate solutions when function has numerical integration in it
I have an equation that is of one variable lat and has a numerical integration in it t from 0 to 1.
Let's say it's given by <...
1
vote
1answer
74 views
Find values of $k$, $l$, and $m$ such that the following equation is satisfied
I am trying to find the (numerical) subset of $(k,l,m)\in[-\pi,\pi)\times[-\pi,\pi)\times[-\pi,\pi)$
where the next expression is valid
$$
\tan \Bigl(
\frac{k+l+m}{2}
\Bigr)
=
\frac{ \sin k+ \...
0
votes
1answer
49 views
How to use a Table to generate numerical data from tridimensional scalar or vector function? [closed]
I am interested to generate numerical values for a scalar and vector function (both are complex functions).
My question and concern are how is possible to evaluate if the functions have three ...
0
votes
0answers
44 views
How to time shift x-axis in mathematica simulation?
I have a simulation from a system of equations that runs from 0 to 50
Normal =
NDSolve[{A /. Parameter, A[0] == .1}, {A[t]}, {t, 0, 50}];
That produces:
Now ...
1
vote
1answer
86 views
Solidification Problems in MMA
can we define such intial value and BCs for a solidification problem in MMA using Finite Element:
1.) initial value:=1 for a plate
2.) in this plate we have to define dirichlet bcs for a whole ...
0
votes
1answer
59 views
Evaluation functions with lower and upper limit ODE?
How do I find the numerical value of y at 0 and also at 1. Here is my code. I appreciate any help.
...
3
votes
2answers
152 views
Solving Equations with HeavisideTheta Functions
I need to solve an equation that involves the HeavisideTheta[] function, but regardless of the method I use Mathematica returns an error message. For example,
<...
1
vote
2answers
157 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
71 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
41 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
60 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
41 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
55 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
175 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
1answer
66 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
126 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
39 views
1
vote
1answer
114 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
121 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
379 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
104 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
43 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
66 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
294 views
1
vote
2answers
118 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
41 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
174 views
Mathematica and IBVP mixing temporal and spatial derivatives
The following PDE's-system-solving code
...
0
votes
1answer
68 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
88 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
<...
1
vote
2answers
59 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
206 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
168 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
112 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
33 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
141 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
123 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 ...
