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

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1
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1answer
191 views

Solving systems of equations

So I have a set of equations like 12 of them but 13 variables. However I would like to find the numerical value of the roots for the maximum value of a particular variable. I don't know how to do that ...
3
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4answers
412 views

Solving puzzles with Mathematica

I would like to be able to solve logic puzzles such as the one described here using Mathematica. I have copied & pasted the listed example below to save on jumping about with hyperlinks: The ...
0
votes
1answer
134 views

Manipulate Solve for initial condition

I have a series of $n$ coefficients with parameters $r$ and $b$ that sum up to one. But there i also the initial condition value $c1$ that i required to obtain this normalization. I want to find this ...
0
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0answers
42 views

Closed solutions for `FindRoot`, no solutions for `Reduce` or `Solve` [duplicate]

Reduce, Solve and FindRoot all appear to struggle with this: ...
1
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0answers
119 views

Using NMinimize to solve the Multi Commodity Flow problem

I have the following optimization problem and I was hoping to solve it with NMinimize. Unfortunately, I don't get the desired result. I would like to get an optimal vector for $d_{e}$. This is how ...
4
votes
2answers
190 views

how to find numerical zeros of $f(z)$ in a compact complex domain

I encountered a function $f(z)$ with several zeros in a region $1<\Re(z)<2, 3<\Im(z)<4$. These zeros are visible in a three dimensional plot like ...
1
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1answer
54 views

How do I solve a profile interval (statistics)

I want to calculate a 95% profile interval for f0. Do worry too much if you do not understand what it is. I will illustrate with a simple example. ...
0
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2answers
82 views

Plot function the uses Solve

Can someone tell me why I get an error (and how I get around it) from Solve while I try to Plot a function like: ...
7
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3answers
204 views

Ovals of plane curves (and esoteric surfaces in space)

Consider the curve $y^2 - x^3 + x=0$ with $x, y$ real. This curve has two connected components (one bounded, one not), and the question is: how do you get Mathematica to tell you that (if you do: ...
2
votes
2answers
205 views

Solving Differential Algebraic Equations as BVP

I am trying to solve a set of DAEs. \begin{equation} -4 \nu (\lambda(s))^{(-1 - 4 \nu)} \theta'(s) \lambda'(s) + (\lambda(s))^{(-4 \nu)} \theta''(s) = -\alpha_y \cos\theta(s) + \alpha_x ...
1
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0answers
95 views

Solving an equation for rational modulus 1

I want to solve an system of equations of the form $$\prod_{i=1}^n x_i^{M_{i,k}}=1 \qquad k=1,\ldots,n$$ with complex $x_i$ with constraint $|x_i|=1$ and $M_{i,k}$ integers. This is basically a ...
0
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1answer
236 views

How to find all roots of a complex number [duplicate]

Finding all roots, and I know there are four f them, of this (1 - i)^(1/4) Not only real, but imaginary as well
2
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3answers
139 views

`Solve` with variables as single vector

Say I have a set of equations where the unknown variables are the elements of a vector $c=(c_1,c_2,\ldots)$ and want to solve it for $c$. Is there a way to do this with ...
5
votes
2answers
1k views

Find all roots in range

Is there any way to check for all roots in a range? Jens' findAllRoots function is pretty good, but runs at approx. 10% of roots missed when I ran a quick check on ...
2
votes
2answers
200 views

Solving 4 variable system of equations

Trying to solve a systems of equations. Here's the code: ...
1
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1answer
127 views

How to calculate minimum positive solution of a equation?

Equations with triangular function usually have multiple solutions, like Solve[Sin[x] == 1/10, x] returns a solution like ...
1
vote
1answer
291 views

How can I stop the integration of NDSolve with a condition?

I try to solve a partial differential equation by NDSolve. At some point, I want to stop the integrating by a condition that compares the min value of the function ...
5
votes
0answers
278 views

What is the algorithm behind Mathematicas Reduce in this equation?

Mathematica can use Reduce to arrive at an answer in this equation ...
2
votes
2answers
244 views

Solving a system of nonlinear equations 2

Regarding this question: Solving a system of nonlinear equations When I try to solve the same system (with the code proposed in Daniel Lichtblau's answer) with different Right Hand Side values, ...
1
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1answer
101 views

Matrix elements scope definition

Alright, I'm very new to Mathematica and I have yet to learn a lot so please bear with me (sorry if this is a duplicate!): I want to create an $n\times n$ matrix $C$ with elements $c_{i,j}$ with $i,j ...
5
votes
3answers
390 views

Not able to get a solution to a Lagrange Multiplier Equation

I assigned several constrained optimization problems to my calc IV students to solve with Mathematica, but this one is being stubborn. The function to optimize is: f(x,y,z) = y Exp[x-z] with the ...
2
votes
1answer
256 views

Problems with NDSolve and partial differential equations of several variables

Suppose we have the following partial differential equation: $$ 0 = \frac{ \partial w }{ \partial \tau } + \left( w + \sqrt{ h + \beta } \right) \frac{ \partial h }{ \partial \chi } $$ where $w$ = ...
1
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0answers
72 views

Creating a matrix from a list of simultaneous equations

I have a list of n simultaneous equations of the form, w A[n] = (K[n,n+1]+K[n-1,n])A[n] - K[n,n+1]A[n+1] - K[n-1,n]A[n-1] ...
1
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1answer
307 views

Find extreme values in a polynomial expression

I have been hunting down and could not find an answer to my question. As I've now been struggling for quite a while and believe it is a simple trick that's preventing me from getting over this ...
3
votes
2answers
209 views

Solve and Reduce with Log finding unexpected root

We give equations like $\ln(1-x)-\ln(x-2)=0$ to our calculus students. This equation clearly has no solution, since $\ln(1-x)$ is only defined if $x<1$ and $\ln(x-2)$ only if $x>2$. Still, the ...
11
votes
3answers
838 views

How can we plot the complex roots of an equation?

If we'd like to display the $n$ roots of a polynomial on the complex plane as points, how can we do this? For example, if we have the equation $x^3 + x^2 + x + 1$, how can we plot the 3 roots as ...
1
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1answer
72 views

Export data from NDSolve when they meet a certain condition

I need to export to a txt file the data from the following system of equations: ...
4
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1answer
472 views

3D Plot of The Riemann Zeta Function

I am a new user and i would appreciate your help to visualize the 3D of the following function. Edit I tried this ...
1
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1answer
83 views

Getting unwanted solution from Solve

I am solving the simultaneously equations $\quad \quad x_7=0$ and $\quad \quad 6x_4x_5+6x_3x_5x_6+zx_4x_7^2+zx_5x_7^2=0$ with Solve. Here, $z$ is an unknown ...
3
votes
2answers
500 views

what to do when NSolve does not solve

f = 696.1125540355472 + 3.9668099604385043 x + LogGamma[1 + x] - LogGamma[169 + x] Plot[f, {x, 0, 10}] Solve[f == 0, x, Reals] NSolve[f == 0, x] I know that the ...
3
votes
1answer
185 views

Importing data from Matlab, using data in “NSolve” and send the results back to Matlab

I have generated an image processing code in Matlab. It has several subroutines and in one of them, I should solve a system of 7 nonlinear equations. I use "fsolve" in Matlab to solve this system, ...
0
votes
0answers
463 views

Poincare Section of an Hamiltonian

I'm in desire to plot the Poincare Section of a differential equation defined by a hamiltonian system. The hamiltonian is as follow: ...
1
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1answer
91 views

Strange functioning of RegionPlot with Reduce's output

I have defined this two quantities: f = (-b + Sqrt[b^2 + 4 a])/(2 a) g = (-b - Sqrt[b^2 + 4 a])/(2 a) and I want to solve this system in function of $a$, for ...
2
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2answers
2k views

Eliminating the Parameter: Transform parametric equation to Cartesian equation and draw arrows along parametric growth

Hey guys I really could use some help on this calc 3 problem. I'm stuck on how to write the code for this problem: a) Eliminate the parameter to find a Cartesian equation for a parametric curve. b) ...
0
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1answer
200 views

NSolve super slow for a parameter scan

I am using NSolve to solve two equations for two variables while scanning through several values of angles. The strange thing is that when I manual enter a value for the angle and Nsolve the answer is ...
2
votes
2answers
285 views

How can I get Solve to combine Sin/Cos into Tan?

I want to solve an equation in x, containing Sin[x], Cos[x] and a positive real constant ...
1
vote
1answer
207 views

Solving a System/Matrix of Equations in Matrix Form

Ok, I am trying to solve an equation involving matrices (well, tensors actually), which is of the form: $\mathbf{e}^{T} \cdot \mathbf{M} \cdot \mathbf{e}$ = $\mathbf{N}$, where $\mathbf{e}$ is an ...
0
votes
1answer
67 views

Solving at zeroes of a matrix - code only works for simple equation

I have a matrix of zeroes (True) and non-zeroes (False). The matrix is generated from a table of values of two other variables. I'm trying to observe how the solution for p3 changes with small ...
2
votes
1answer
418 views

Solving a system of nonlinear equations

The bellow set of equations has two answer sets for (α1, α2, α3, β1, β2, β3) respectively as following: (3, 1, 3, 1, 1, 1) & (3, 0.75, 3, 0.5, -1, 0.5) ...
0
votes
0answers
140 views

No solution with DSolve

I have been trying to solve the following system of ODEs: \begin{eqnarray} ...
1
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0answers
63 views

Finding related roots to a polynomial

I posted this in math.stackexchange, but this might be a better place. Assume that $f(X,Y,Z,V,W)\in \mathbb{Z}[X,Y,Z,V,W]$ is some polynomial and assume that $f(x,y,z,v,w)=0$. I would like to know if ...
2
votes
3answers
128 views

MapAt a function at specific positions

I'm trying to solve for $p3$ in 3p3-5 = p1 + p2 at positions where p1*p2 == 0: ...
2
votes
2answers
330 views

Given a system of inequalities, how to make Solve find out that two variables should be equal?

Given two boolean variables x1 and x2 (in the sense that they are in the range [0,1]), if I try to solve the following equation system with Solve: ...
1
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2answers
92 views

Error using Nsolve with system of two equations: “Use Reduce”

Having some odd behavior with some mathematica code I am running. I am solving a simple system of two equations but mathematica gives an error and asks to use Reduce? I looked up in the manual but ...
0
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0answers
59 views

solving nonlinear equation

I typed this below code in mathematica 9.0 but wasn't solved: ...
1
vote
1answer
217 views

FindMinimum and NMinimize to solve equations

I know that I'm not a Jedi in solving Equations and minimizing functions; but now I've this problem, and the solution is far to me. I want to solve this equation: ...
1
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1answer
157 views

How smart is Solve? Figuring out what tricks I should try

I'm trying to solve a large system (~10000) of linear equations using Solve, but the process keeps failing. As-is, I don't know whether it's failing because it's using too much memory or too much time ...
8
votes
4answers
230 views

Combining solutions while solving

Here is a simple representation of my problem. I want to solve Solve[(w^2*c^2 /. #) - 1 == 0, w]& /@ {{c -> 1}, {c -> 2}} ...
1
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1answer
110 views

Applying N to the roots found by Solve gives complex numbers when the roots are real [closed]

I have a function which is f(x) = x^3 - 5 x^2 - x + 1. When I solve for x to find the zeros ...
2
votes
2answers
295 views

How to explain NDSolve that functions must be positive only?

I have a simple system of differential equations to solve but both functions should be positive: x[t] > 0 and y[t] > 0 for all t. I was not able to explain NDSolve this fact so it goes x[t] < 0 ...