Questions tagged [numerical-value]

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

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69 views

Why mathematica does not solve the equation $x\left \lfloor x \right \rfloor=10$ for $x$?

The equation $x\left \lfloor x \right \rfloor=10$ has a real solution, which is $x=\frac{10}{3}$. But when I type Solve[x*Floor[x] == 10, x] a message comes: "...
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1answer
31 views

Formula: setting parameters vs replacement, different results?

I have a question that may sound stupid and have an easy answer - but I currently do not see it. I have defined a function of four variables, $f[a,b,c,d]=...$, in what I think is correct Mathematica ...
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1answer
51 views

Problem of Encountered non-numerical value for a derivative at t == 0

I try to solve this equation numerically : eq= z''[t] + (2691+ D[Log[Abs[z'[t]^2]],t]) (z'[t]^2 + Abs[z'[t]]^2 ) == 0; By ...
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3answers
142 views

Different Methods in NIntegrate

I am trying to numerically calculate a multidimensional integral which involves Jacobi elliptic theta functions. The integrand is the following: ...
3
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1answer
51 views

NumericQ and unknown number of variable in a module-block

I have the following problem I want to address in an elegant way. I have a function of many variables f[x, y, z,...] I want to find the minimum with ...
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1answer
82 views

Why does Integrate return an unexpected imaginary solution?

When I calculate the value of the following integral using Integrate, I receive an unexpected imaginary solution. I am using Mathematica 11.3.0. ...
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0answers
32 views

Nintegrate providing results much smaller than what is expected

This is the first time I am posting something here. So, apologies if I make any mistake. I am dealing with a numerical integration in Mathematica-11.0 that has a Bessel function in it. In order to ...
1
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1answer
31 views

Numerical solution to an equation that doesn't have an analytic form

Suppose I have an equation $$ d=\int_A^B \dfrac{dr}{\sqrt{1-\dfrac{2M}{r}}}\\ =B\sqrt{1-\dfrac{2M}{B}}-A\sqrt{1-\dfrac{2M}{A}}+M\ln\left( B\sqrt{1-\dfrac{2M}{B}} +B-M\right)-M\ln\left( A\sqrt{1-\...
5
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1answer
126 views

1-D PDE with nonlinear ODE as boundary condition

Recently, I am trying to solve a 1-D PDE with a nonlinear boundary condition using the function NDSolveValue. However, it seems that MMA (12) cannot solve it directly with some computational issues. ...
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0answers
61 views

Numerical evaluation expression not returning result in requested precision

I have a long list of descriptive statistical quantities for a univariate list of data. The problem is that the set number of significant figures is ignored by the ...
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0answers
32 views

Setting the tolerance for `Equal[]` [duplicate]

I would like to control how Equal[] works and allow a certain error associated with it. I would like numerical values which are, say, within one-thousandth of one ...
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1answer
37 views

Evaluating functions for different values of parameters

here it is my question. I have a system of two equations in two variables, so I can get a solution. The issue is that those equations depend on three parameters, so my solution will depend on their ...
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0answers
27 views

Preventing mathematica from evaluating “Sort” function, except in the case of numerical values

Say I want to sort the eigenvalues E1, E2, and E3 using "Greater" as following: {EA, EB} = Sort[{Chop[E1], Chop[E2], Chop[E3]}, Greater][[{1, 2}]]; But I want ...
3
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1answer
64 views

How to use NDSolve to solve 1+1 D heat equation $u_t=u_{xx}$ with $ -\infty<x<\infty$ and $0\leq t\leq T$?

How to use NDSolve to solve 1+1 D heat equation $u_t=u_{xx}$ with $ -\infty<x<\infty$ and $0\leq t\leq T$? ...
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0answers
32 views

Problem with NMaximize and intervals

My expression is ...
3
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2answers
656 views

Mathematica will not solve this numerical equation

I have the following equation: ...
2
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2answers
41 views

Testing Positivity of Interpolating Function

I have an interpolating function and I want to test whether it is positive definite over an interval. Will any of Mathematica's numerical optimisation functions work for this or is there a simpler ...
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1answer
42 views

NIntegrate does not evaluate this finite integral composed of divergent parts

I would like to numerically evaluate the following integral: $$I = \int_{-\infty}^\infty d\tau_3 \int_{-\infty}^\infty d\tau_4 \frac{1}{1+\tau_3^2} \left\lbrace \frac{2}{1+\tau_4^2} \log (\tau_3 - \...
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0answers
48 views

Numerical estimates on a given functional [duplicate]

Consider the following functional : $$ I(x,s) =\int_0^\infty\mathrm dy \frac{F(x + \mathrm iy, s) − F(x −\mathrm iy, s)}{\mathrm e^{2πy}-1}, $$ where $ F(z, s) = \dfrac{\sinh(\sin^2[π\Gamma(z)/(2z)])...
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1answer
56 views

Hypergeometric function not giving a numerical value [closed]

I tried to run the following code: ...
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1answer
59 views

Which command can I use to obtain numerical solutions of a two-variable equation? [duplicate]

Regarding my previous question, which command I can use to obtain the numerical solutions of a general two-variable equation: f[x_, y_] := 0 for some specific ...
3
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2answers
580 views

How to obtain numerical solutions of a two-variable equation?

I have a two-variable function: f[x_, y_] := (4 y^2 - 6) (Cos[y π] Cos[x] - Cos[2 y π] Sin[x]) How can I find all the numerical solutions for $x$ and $y$ such ...
3
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2answers
468 views

Solving an equation approximately

I have a complicated equation in terms of $\omega$ and $\kappa$: ...
1
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2answers
55 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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0answers
108 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
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1answer
87 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
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1answer
173 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
69 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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1answer
48 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 ...
3
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1answer
103 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
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2answers
79 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
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2answers
267 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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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 ...
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1answer
26 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
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1answer
78 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
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1answer
51 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
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0answers
49 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
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1answer
90 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
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1answer
61 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
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2answers
158 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
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2answers
159 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
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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 ...
1
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1answer
46 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
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1answer
65 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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0answers
43 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
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1answer
58 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
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2answers
192 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
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1answer
72 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 ...