Questions tagged [numerical-value]

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

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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 ...
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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: ...
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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 ...
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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 ...
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182 views

Why program output produces 0 / 1 error

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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 ...
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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 ...
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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 ...
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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 ?
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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 ...
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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 ...
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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 ...
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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: ...
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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 ...
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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 <...
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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+ \...
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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 ...
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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 ...
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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 ...
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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. ...
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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, <...
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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 <...
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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 ...
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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, ...
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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 <...
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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,\...
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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. ...
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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 ...
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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 ...
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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 ...
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1answer
39 views

Reverse the reccurence mirrorwise

Let be a recurrence for polynomials $R_{m,j}$ ...
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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 ...
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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, ...
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2answers
379 views

Can one define 0 Log[0] = 0?

With reference to this post, can one define 0 Log[0] = 0 in Mathemtica?
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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 ...
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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 ...
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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: ...
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3answers
294 views

N[…, 5] does not returns what I expected

I have this ...
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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 ...
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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)+...
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1answer
174 views
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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...
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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 <...
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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 + ...
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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 ...
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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 ...
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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:...
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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 ...
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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 $...
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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 ...