# Tagged Questions

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

126 views

### Numerical solution of two equations in two functions

I would like to obtain a solution to the following two equations, where g0[y] and g1[y] are the unknown functions: ...
28 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 ...
71 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 ...
261 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 ...
68 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 ...
390 views

### A problem with polynomial root finding

I use the expression ...
131 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, ...
133 views

### Many NSolves to interpolating function

I have an expression of the form: expr = TerribleNumericalFunction[U[p]] == SimpleFunction[p] The Simple function is a ...
198 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.
164 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[()), \ (2)])-25(1-!(*FractionBox[...
379 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: ...
85 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: <...
88 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: ...
283 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 ...
202 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 ...
165 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: ...
71 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 [...
139 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 ...
256 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 ...
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] ...
270 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 ...
202 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 http://math.stackexchange.com/questions/1385633/solving-sde-fracdytdt-c-sigma-wwtyt-...
78 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 ...
123 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: ...
326 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 ...
112 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 11....
47 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 ...
73 views

### Matrix issue with NDSolve

I am solving a differential matrix equation with NDSolve. ...
123 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 ...
608 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 ...
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 ...
93 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 ...
82 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 ...
125 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 ...
254 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 ...
119 views