Questions on the analytic and numeric equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).

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3
votes
1answer
107 views

Computing planet conjunctions with 2D circular orbits still hard?

All methods I've seen for computing planetary/stellar conjuctions (when two planets or a planet and a star appear close together in the sky because their angular separation, as measured from Earth, ...
1
vote
3answers
116 views

Many NSolves to interpolating function

I have an expression of the form: expr = TerribleNumericalFunction[U[p]] == SimpleFunction[p] The Simple function is a ...
4
votes
4answers
160 views

How to find roots of equation

Solve[(Cos[θ] - Cos[θi]) + (θ - θi)*Sin[θi] == 0, θ] Hi, I am new to Mathematica, and I am trying to find roots of the above equation, but not success.
-1
votes
1answer
79 views

What am I doing wrong when using Solve ( Wolfram Alpha)

It is not because we do not interpreted correctly WolframAlpha["Solve[64(!(*FractionBox[(x - *SqrtBox[(*SuperscriptBox[(x), \ (2)] - 1)]), (x + 1)]) !(*SuperscriptBox[()), \ ...
3
votes
1answer
86 views

How to change parameters to equations of physical properties they belong to in an equation?

First off, I want to apologize for my poor English as I am not a native speaker. In my physics research, I had to solve a system of equations, from which I would get a solution for the speed of an ...
14
votes
2answers
330 views

FindInstance returns Indeterminate in version 9, but not in 8

Bug introduced in 9.0 and fixed in 10.0.0 Here is a trivial system of equations in three unknowns for which FindInstance obtains a solution: ...
1
vote
0answers
70 views

Solve struggling with two equations in two unknowns

I have a two equations and two unknowns. I tried to solve the equations with Mathematica, but it is having trouble. It has been saying Running... for quite a long time. Here is my system: ...
0
votes
1answer
57 views

Problems with solving two coupled lorenz equation with NDsolve

I have a system of two coupled lorenz equations and I'm to integrate it: ...
8
votes
1answer
155 views

Using a Mathematica index as a DiscreteVariable in NDSolve when solving a coupled set of ordinary differential equations

Context Since the explanation below of the problem to be solved is lengthy, let me preamble this by saying that I have code that works to solve the problem, but I don't know whether (1) it's ...
1
vote
2answers
141 views

Solve a symbolic underdetermined Linear System

Dear StackExchange Community, I'm trying to solve an indeterminate linear system of equations, with $n+1$ variables and $n$ equations; therefore, I need to express all $n$ other variables a function ...
6
votes
1answer
108 views

Why is Solve slow for one representation and fast for an equivalent form?

When I try to solve the following: Solve[(1 - (-1 + x)^- x)^8 == 95/100 && x > 1, Reals] solve chokes. If instead I use the equivalent form: ...
2
votes
1answer
52 views

Most simple example where series expanding a root object actually fails due to branchcuts

When computing the series expansion of a Root object Mathematica throws an error like: "Because of branch cuts, the series may represent a different root of [root expression] for some values of ...
12
votes
1answer
126 views

Strange result of Reduce and ForAll

In the question Can Mathematica tell me if a polynomial has all real roots?, quite a few of interesting answers were given. I wanted to add another one, using quantors, and observed some strange ...
2
votes
1answer
105 views

Solve overdetermined set using Mathematica?

As shown below, this is a overdetermined system. Could you teach me how to find the optimized solution in Mathematica? I know it could be solved by the method of least square, but how to realize it in ...
0
votes
0answers
57 views

The system can not be solved

I'm trying to solve this equation: f[a_][r_]=((a*r/12)*(1+(r/12))^n)/(((1+(r/12))^n) - 1) When I type Solve[f[a][r]==p, a] ...
4
votes
3answers
256 views

Solving $(-1-z)^n = z$, for $z$ in the unit circle

I want to solve the following equation: $$(-1-z)^n = z,\quad |z|<1,\quad n>1\in \mathbb{N}$$ where $z$ is a complex number. However Solve or ...
0
votes
0answers
37 views

How to solve algebra equations containing integration and parameters?

I'm trying to solve two nonlinear algebra equations for two unknown parameters, U and Tf. Since some terms in these equations contain integration, and the integration also contains U and Tf. The main ...
3
votes
0answers
71 views

Solving for the roots of a trilinear system of polynomials

I have been trying to solve for the roots of the following system of trilinear polynomials: ...
2
votes
1answer
124 views

Solving SDE: $\frac{dy(t)}{dt}=(c+\sigma_wW(t))y(t)+\epsilon(t) $ in Mathematica

I want to solve this differential equation $\frac{dy(t)}{dt}=(c+\sigma_w W(t))y(t)+\epsilon(t) $. For details see ...
0
votes
0answers
39 views

solving dynamic system by a finite difference equation approximation

I have a four dimensional dynamical system from optimal control model. I have 2 states and 2 control variables. I have already found the corresponding initial conditions for two control variables for ...
0
votes
2answers
53 views

How to find ANY solution to an underdetermined system of equations?

I have certain systems of equations for which I need ANY solution if one exists. Can I get MMa to just do that? This doesn't work: ...
25
votes
1answer
285 views

Solve slower in versions 9 and 10

With some systems of equations, Solve is much slower in versions 9 and 10 than in earlier versions, apparently because it is doing more simplification of the ...
0
votes
2answers
91 views

Find *all* numerical solutions to cosine based equality

To help with http://astronomy.stackexchange.com/questions/11456/ I'm trying to find all numerical solutions to: 5.20427*Sin[0.529699*t] == Sin[2*Pi*t] Since the period of the first function is ...
2
votes
0answers
40 views

NDSolve with NIntegrate [duplicate]

I'm new to Mathematica and I'm trying to use it to solve some equation like: NDSolve[x'[t]+NIntegrate[x[tau],{tau,0,t}]==20,x,{t,0,10}] But it keeps giving me ...
1
vote
1answer
47 views

Matrix issue with NDSolve

I am solving a differential matrix equation with NDSolve. ...
2
votes
1answer
90 views

Problem in understanding PDE solution

I solved the PDE shown below and I got the solution. I am new to this tool. In the solution, I have a constant multiplied by a vector like function (please refer second term of the solution). What ...
4
votes
2answers
528 views

Order of a pole

Is there a simple way to determine the order of the poles of a rational function? I have a difficult function where I need Mathematica to find the poles. It would be interesting to also know what the ...
0
votes
0answers
21 views

Plotting a dispersion curve with complex wavevectors [duplicate]

I want to reproduce a dispersion curve from P. Zou's thesis found here: http://www.ipd.anl.gov/anlpubs/2001/06/39620.pdf on Pg. 31, Eq. 2.13. The problem is, the code below only gives values for the ...
3
votes
1answer
71 views

Easy way to solve a matrix equation for a matrix?

I have two sets of $10\times 10$ matrices $M1,M2,M3,M4,M5$ and $N1,N2,N3,N4,N5$ and I want to solve a set of equations for these matrices ...
6
votes
0answers
64 views

Choosing appropriate WorkingPrecision when solving numerical system of equations

Consider a linear system of equations, which is conveniently written as A.x=y. The matrix A has dimensions ...
2
votes
0answers
74 views

Suggestions for solving a large linear system

I have a system of $\approx 200,000$ linear equations in $\approx 40,000$ variables (with rational coefficients) and I would like to determine the dimension of the solution space, which I know to be ...
8
votes
1answer
233 views

FindRoot kills kernel

Bug introduced in 7.0 or earlier and fixed in 10.1.0. I'm having problems with FindRoot killing the kernel. In my real application, I want to ...
5
votes
2answers
109 views

How to use ForAll to prove things about functions?

Suppose I first declare: $Assumptions = ForAll[{a,b}, b > a, f[b] > f[a]] I (wrongly, as it turns out) assume that that this would cause ...
0
votes
0answers
42 views

Trying to find parameters for a system of inequalities

So I have a system of 4-dimensional system of ODEs and I'm trying to find any values of parameters that satisfy properties I need. In this picture, I want two basins of attraction, one of which the ...
0
votes
1answer
56 views

More issues Integrate, NIntegrate, FindRoot

I'm trying to solve a system of 3 non-linear equations using FindRoot and Integrate. If I start FindRoot[] close to the right answer, it works well but returns a bunch of error messages first. ...
0
votes
1answer
52 views

Problem with solving coupled differential equations

The following code seem to produce an output that appears to be independent of the parameter "fg". It is possible that the way the code is written might be causing it, but how can one fix this ...
6
votes
1answer
353 views

How to get vertices of a polytope given by equalities and inequalities?

I have a polytope given by some equalities and inequalities, how can I get all the vertices of the polytope? If there's a way to deal with the one given by inequalities only, how can I reduce the ...
2
votes
1answer
99 views

Solve an inequality involving a sum with a parameter

Good day. I am new to Mathematica and I am looking for advice. Is it possible to solve $$\sum_{k=0}^{n} \frac{p^k}{k!}>0$$ for $n$ where $p$ is a parameter? When I do ...
1
vote
0answers
128 views

Numerical solution to integral equation

I have an integral equation where one factor $f(t)$ in the integrand is defined in terms of an integral equation where it is again a factor. $\quad \quad y[t]=\int _0^tf[\tau ]g[t-\tau ]d\tau + ...
9
votes
3answers
402 views

Trouble getting FindInstance to return multiple results for certain constraints

I'm having a hard time getting FindInstance to return multiple results. Consider this simple example: ...
1
vote
2answers
236 views

Problems finding intersection points between line and generic function

I'm trying to find Intersection points between a line, which is given by 2 points, and a generic function (I want it to be able to handle polynomial functions, circles/ovals, lines and all ...
4
votes
2answers
50 views

Inputting values into the variables without having to input the matrix all over again

I'm practicing using LU decomposition on Mathematica. I am able to find the L & U matrices, specifically the variables. However, i find it tedious having to input the newly found values and form ...
2
votes
1answer
125 views

Equation involving hypergeometric functions

I want to solve this equation but nor NSolve nor Solve are able to do this. ...
14
votes
1answer
271 views

What Method options does FindInstance accept?

While answering Trouble getting FindInstance to return multiple results for certain constraints it became clear that for this problem FindInstance would be better ...
11
votes
1answer
172 views

Using Simplify on a consistent system returns False

Bug introduced in 8.0 and persisting through 10.2 or later It's late, but am I missing something here? Why should two independent equations, which together are consistent, ...
2
votes
1answer
88 views

Potential flow over cylinder with FEM: Pressure field is flipped

Much in the fashion of a few problems already answered on Mathematica.SE (1, 2), I am trying to solve the Laplace equation in velocity potential $\phi$ to simulate irrotational, inviscid flow over a ...
0
votes
0answers
26 views
0
votes
1answer
64 views

Multivariate Equation solving [closed]

I have the following equation: r^(1 + Rho) - r^Rho (-1 + Mu) - z Rho == 0 I searched the list but I couldn't come up with a solution. Any help is appreciated. ...
1
vote
0answers
53 views

Use Solve[] with Bessel, gamma, and hypergeometric functions?

I need to find values of {a,b,c} such that the 0th, 2nd, and 4th order moments of f[x]=Exp[-ax^4 - bx^2 - c] will equal respectively {1,2,10}. I didn't really expect this to work, and it didn't: ...