Tagged Questions

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

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0
votes
0answers
55 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 ...
1
vote
3answers
45 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 ...
2
votes
2answers
126 views

Solving 4 variable system of equations

Trying to solve a systems of equations. Here's the code: ...
1
vote
1answer
57 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 ...
0
votes
1answer
64 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 ...
4
votes
0answers
202 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
184 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
vote
1answer
77 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
192 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
117 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 $w$ = ...
0
votes
0answers
62 views

Undocumented options for NSolve

There are many undocumented options in Mathematica's official documentation. Is there a tutorial, or a reference somewhere, that explains in detail the undocumented uses of ...
1
vote
0answers
65 views

Numerical solution to two non-linear coupled differential equations [closed]

I am trying to solve two differential equations representing the position of an object in space. I have specified arbitrary initial conditions. ...
1
vote
0answers
42 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
vote
1answer
91 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
134 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 ...
0
votes
0answers
45 views

Faster way to use Solve in a multiple parameters function

I have a complicated function, G, of several arguments: $G[{\lambda1,\lambda2,a,b,c,d,\sigma u,\sigma v,\rho,q}]$. First, I want to fix a=0.5,b=0.7,c=0.4,d=0.35, q=1. Then, I need to find the values ...
1
vote
1answer
52 views

How do I find the expression for where the first derivative equals 0? [closed]

I have a simple function of time. If I take the first derivative and set it equal to 0.0 I get the extrema of that function. I'm not interested in a numerical result, I want an expresion involving ...
1
vote
1answer
51 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: ...
1
vote
1answer
57 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 ...
2
votes
2answers
61 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 ...
1
vote
1answer
32 views

Error following a variable in an ODE [closed]

I am trying to solve a 4th order differential equation and this is my code thus far ...
0
votes
0answers
33 views

Boundary condition is not specified on a single edge of the boundary of the computational domain

When I want to solve this PDE I get this error "NDSolve::bcedge: "Boundary condition u[0,0.05]==0 is not specified on a single edge of the boundary of the computational domain"" ...
3
votes
1answer
96 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
118 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
vote
1answer
53 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 ...
1
vote
2answers
183 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) ...
-2
votes
1answer
68 views

Solve a system of two equations only in Mathematica [closed]

x + Sinh[x] == Sin[y] + y z + Exp[z] == x + Log[1 + x] + 1 M={0,0,0} x-? y-? z-? Solve[] doesn't solve this system.
0
votes
1answer
93 views

Attempt to solve for Differential Equation - Acc, Vel, Pos in (x,y,z) [closed]

In the problem I'm working on, there is a tennis ball that is subjected to a headwind, tailwind, and crosswind. I am trying to use NDSolve in order solve for the position functions and to eventually ...
0
votes
1answer
69 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
127 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
102 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
61 views

Display solution of Solve without the arrow [closed]

Is there a way to format Solve or something that I get the result of a calculation without the arrow, so if my result is like ...
0
votes
1answer
61 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
270 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
61 views

No solution with DSOLVE

I have been trying to solve the following system of ODEs: \begin{eqnarray} ...
2
votes
3answers
112 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
148 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
vote
2answers
77 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
votes
0answers
53 views

solving nonlinear equation

I typed this below code in mathematica 9.0 but wasn't solved: ...
1
vote
1answer
87 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: ...
0
votes
1answer
113 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
187 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}} ...
2
votes
2answers
257 views

How can I get this sum? [closed]

I want to sum the following numbers. At present I am calculating my sum as follows. a = 10^20 + 10^30 + 10^40; In the above case, if I want to add 100 or more ...
1
vote
1answer
88 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 ...
1
vote
2answers
98 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 ...
1
vote
0answers
77 views

Comparing two ways of fitting systems of ODEs to data

I'd like to ask you if you see any difference between the two following ways of estimating parameters. Given my system of ordinary differential equations that I want to use to find the values of all ...
1
vote
0answers
68 views

Stability region of midpoint method using Solve and RegionPlot

I've been trying to obtain the stability region in the $(\lambda_R, i\lambda_I)$ plane of the midpoint rule $$y_{n+1}= y_{n-1}+2h\dot{y}_n,$$ for the model problem $\dot{y}=\lambda y$. The roots for ...
0
votes
0answers
78 views

Rearranging 5 equations

I am trying to rearrange 5 equations in terms of 5 variables. I have the equations for y1, y2, ...
1
vote
1answer
67 views

How to solve this equation?

Mathematica does not give me the correct solution (-1) for this equation: Solve[9^(x + 4) == 27^(1 - x), x] Do I miss something or is Solve the wrong approach ...
1
vote
1answer
81 views

NSolve for complicated equation involving double cross product

I have the following issue. I am trying to solve a 3-vector equation for the vector slx, sly, and ...