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

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4
votes
0answers
77 views

Method of characteristics, recursion formulas

I'm helping a friend out with a problem. He needs to plot out the solution to a water surge in a pipeline. I have all the parameters set and I've put the equations in Mathematica, but I can't get the ...
2
votes
1answer
120 views

How to solve coupled complex-valued equations faster and get simplified solution

I have six coupled equations. How to solve these equations symbolically faster in Mathematica. In these equations, variables p,q,x,y are ...
1
vote
2answers
173 views

Trying to solve a system of equation

I am trying to solve 3 equations 3 unknown system on Mathematica in order to get numerical results for my three variables x,y,z but the software is always on the ...
1
vote
2answers
72 views

Condition on Inside of Region

How do I handle boundary conditions present in the region. Mathematica complains about the condition v [1 , t ] == u [1,t]. The condition should be given to this ...
3
votes
1answer
61 views

Reduce return a strange result for solving a equation with radical

Reduce[1/Sqrt[x] == x + 1/(Sqrt[2] + Sqrt[3]), x] the output is unreadable and include the symbol Reduce`CADAlgVar[1].
0
votes
1answer
65 views

what am i missing? [closed]

An attempt to solve ...
4
votes
0answers
71 views

Reduce doesn't solve this equations with condition

Reduce[{4==Abs[-1+2 Cos[2A]+2 Cos[2B]+2 Cos[2(A+B)]]},{A,B},Reals] worked well, but ...
1
vote
0answers
27 views

Minimizing values of expressions dependent on more variables [closed]

I need to enforce seven expressions dependent on seven variables to be zero. However, the expressions are quite complicated and generaly I get a system of transcendental equations which only sometimes ...
20
votes
3answers
1k views

How to find numerically all roots of a function in a given range?

It is common that I search numerically for all zeros (roots) of a function in a given range. I have written two simple minded functions that perform this task, and I know of similar functions on this ...
0
votes
1answer
69 views

NDSolve does not satisfy initial conditions

For the problem I'm facing, I have three coupled diff eqns that I'm trying to solve ...
0
votes
2answers
241 views

How to solve a pair of coupled 2nd order equations using shooting method

I have a pair of equations for x[t] and y[t]. Both are 2nd order and they are coupled. Now say that I know the following ...
0
votes
0answers
67 views

Equations in a quadratic field

I would like to solve a system of equations in a quadratic field, meaning that each variable $x$ of my system can be written $a + b \sqrt{d}$, where $d$ is a fixed value. Suppose for example that I ...
3
votes
1answer
128 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
votes
1answer
137 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
208 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 ...
4
votes
4answers
197 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
vote
0answers
83 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
84 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: ...
6
votes
1answer
155 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
69 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 ...
0
votes
0answers
59 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] ...
2
votes
1answer
211 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 ...
2
votes
2answers
194 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 ...
0
votes
0answers
62 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 ...
4
votes
1answer
126 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: ...
0
votes
0answers
71 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
109 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: ...
0
votes
2answers
109 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
1answer
199 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 ...
2
votes
0answers
45 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
71 views

Matrix issue with NDSolve

I am solving a differential matrix equation with NDSolve. ...
2
votes
1answer
120 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 ...
0
votes
0answers
23 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 ...
4
votes
1answer
84 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 ...
7
votes
0answers
81 views

Choosing appropriate WorkingPrecision when solving numerical system of equations [closed]

Consider a linear system of equations, which is conveniently written as A.x=y. The matrix A has dimensions ...
5
votes
2answers
118 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
1answer
94 views
3
votes
0answers
121 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 ...
0
votes
1answer
135 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
62 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 ...
0
votes
0answers
56 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 ...
28
votes
1answer
323 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 ...
4
votes
2answers
60 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 ...
0
votes
0answers
34 views

How to use function, NIntegrate, FindRoot together? [duplicate]

Using a function in NIntegrate works fine... ...
2
votes
1answer
306 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
1answer
79 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. ...
2
votes
1answer
122 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
70 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: ...
5
votes
2answers
596 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 ...