Questions tagged [equation-solving]

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

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13 views

NDSolve::conarg: The arguments should be ordered consistently mistake

I want to solve a system of differential equations, but I get NDSolve::conarg: The arguments should be ordered consistently mistake. How can I avoid that? code: ...
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3answers
1k views

Solve Laplace equation in Cylindrical - Polar Coordinates

Hey mathematica stackexchange!! I've got a (possibly stupid) problem. I've tried many things to no avail, and I've read every post I've found on Laplace's equation. Background: I'm trying to find the ...
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1answer
39 views

Solving complex trig quations - missing solutions?

{ Sin[Pi/2 + I*Log[2 + Sqrt[3]]], Sin[Pi/2 - I*Log[2 + Sqrt[3]]], Sin[Pi/2 + I*Log[2 - Sqrt[3]]], Sin[Pi/2 - I*Log[2 - Sqrt[3]]] } // FullSimplify ...
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3answers
211 views

Defining a big matrix for iterative algorithm

I need to solve this system of equations with Seidel and Jacobi methods, so I tried to define a big matrix in Wolfram. I have read documentation, and I wrote the following command that should help me,...
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0answers
37 views

FindMinimum giving wrong answer

I have a very simple problem that Mathematica is giving a wrong answer to. I want to minimize the following function: $\frac{3+t^2+6\theta +3 \theta^2}{6 t^3}$ in $\theta$ and $t$. Now, plotting the ...
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1answer
56 views

Solution of a system of ODE with Dsolve

I am trying to solve following ODE with Dsolve. a1[t_] = 2 - 3*Exp[-2*t]; a2[t_] = 1 + Exp[-3*t]; a3[t_] = 4 + Exp[-5*t] $B=\begin{bmatrix}a1[t] & a2[t] &...
3
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1answer
68 views

Is there an alternative way to solve this equation?

Any suggestions to obtain $x$ in terms of $n$ in this equation. Again Mathematica gives: "This system cannot be solved with the methods available to Solve." $\coth (\pi x) \coth (n x)-\frac{x^4-2 x^...
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1answer
55 views

How to substitute by NDSolve solution to plot a new function

Assume I got some function by NDSolve , like y(t) ...
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1answer
68 views

Solve the vector-matrix equation. Minimize the length of the desired n-dimensional vector

There is the following vector-matrix equation. where C - nonzero constant. [x1 x2 ... xn] - vector of real numbers. M - matrix of real numbers of dimension n x n It is required to find a vector $x$...
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1answer
110 views

Finding the inverse of a function

I am to solve for $r(\rho)$ given the function, \[Rho]Asymp[r_,b_,q_] := 1/(1 - q) Gamma[1/(1 - q)]/Gamma[(q - 2)/(q - 1)] r Sqrt[1 - (b/r)^(1 - q)] This can be ...
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0answers
57 views

How to solve this equation in Mathematica?

I wonder what is the best way to solve this equation in MA? $$ y= \frac{\partial}{\partial x} ~ \frac{\partial}{\partial x^*} f $$ where y and ...
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2answers
51 views

Trying to to replace Root expressions from the output of Eigenvalues by the explicit forms

When I calculate the eigenvalues of the following matrix (H) by using Eigenvalues, I get complex expressions with ...
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0answers
31 views

Solving equations with two parameters

There are two equations: Integrate[1/Square(2*Cosh[y] - 2*Cosh[u]) , {y, z, u}] == 0.013 2*Cosh[z] - 2*Cosh[u] == 0.41 How can I obtain z and u?
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1answer
41 views

Numerically solve system of equations with nested variables

I'm trying to solve the following system of equations. The first two equations depend on the variable TeV ...
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0answers
27 views

FindRoot with constraint that the variables are not equal

I have this system of equations : ...
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3answers
102 views

Problem with NSolve with Logarithm

I have an issue with NSolve, and I think it's because of the logarithms : ...
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1answer
76 views

Solving these equations with a constraint

I have been for long time now try to solve this equation q1[t_] = D[x[t], t, t] - 2 (1/y[t]) D[y[t], t] D[x[t], t] With its complex conjugate ...
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1answer
48 views

Solving a system of linear equations with a For-loop

I need to find the value of c1, c2, c3, c4 and c5, but the output from my code is the simplified equations, not the exact value ...
3
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1answer
53 views

Can Mathematica check ansatz for solutions of differential equations?

I'm just a beginner learning Mathematica. I'd like to do something with it, but I don't know if it is possible. Suppose I want to solve a system of differential equations, maybe a nonlinear one, and ...
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2answers
28 views

NIntegrate user defined function

I have the the function f[a_] := Module[{solution, ans, x}, solution = NSolve[x + a == 4]; I want to integrate it by writing ...
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2answers
50 views

Solve system of equations does not match

I have the following system of equations: ...
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0answers
49 views

Why maple returns nothing on this diff equation? [closed]

I am very new to this software. I have a differential equation, but when I run this code, it gives me back wrong statement of {x} as a symbol variable... What should I specify more on this equation? ...
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0answers
26 views

Problem in solving a trancedental equation which is embedded in module

I have written a small program to compute the resonance frequency, for that I am solving a transcendental equation, which comes from the determinant of the matrix ...
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1answer
752 views

Restricting Solve to positive reals

I want to restrict the solutions to Solve to the positive reals. This is my code: ...
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0answers
53 views

how to solve nonlinear differential equations which calls other functions that uses states and time as input while solving NDSolve?

I have nonlinear differential equations which require output from other functions and those functions require time and some states as input. I'm writing the Mathematica code bellow the equation. $p=...
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2answers
79 views

Why is FindRoot so slow for this problem Det[M[x]]==0

I'm trying to use Mathematica to find the numerical solution to an equation Det[M[x]] == 0, where M[x] is a matrix function of <...
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0answers
174 views

Spurious DSolve Solution

Bug introduced in 8.0.4 or earlier, persisting through 12.0. DSolve quickly returns solutions to the following PDE (which is the homogeneous portion of the PDE in ...
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1answer
88 views

Symbolic matrix equation with summation

Considering a set of points: Let Matrix A be: And B: Where $\bar{x}$ is given by: And the same goes for $\bar{y}$ and $\bar{z}$. I want to solve this equation: But without specifying any values. ...
4
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3answers
107 views

Solve works with symbols, not with numbers

I don't understand why, in the code below, Solve works with symbols, but substituting numerical values (rational) for the symbolic parameters makes it unsolvable: ...
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0answers
41 views

What is the algorithm used by SolveAlways function?

The syntax of SolveAlways function is SolveAlways[eqns, vars] For example, SolveAlways[ax + b == 1, {x}] Mathematica ...
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2answers
197 views

Approximating the density of $S\cap[a,b]$ using a Folner Sequence of $A$, where $S \subseteq A$?

Edit: I redid my code but it's still not working. How do we use Mathematica to approximate $$D(S\cap[a,b])=\lim_{n\to\infty}\frac{\left|S\cap{F_n\cap[a,b]}\right|}{\left|F_n\cap[a,b]\right|}$$ ...
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2answers
93 views

Why am I unable to solve this system of equations?

I don't know why I can't solve this system of equations in Mathematica. I just want to find $p_{i,j}$ terms that satisfy $\pi_0 * P^3 = \pi_1$, as seen here. But I'm getting an error that this isn't a ...
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1answer
23 views

Reduce and Expand solutions after Solve

I solve a system of 4 equations with 4 variables z_i (see below). I would like to change the way results are written as such for each i: y_i = AX + sum[By_(-i)] + Cz_i + u_i where the sum comes from ...
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3answers
57 views

Solve for coefficients to express polynomial in terms of another polynomial

If I have a polynomial, say $p(x) = 6x^3 - x^2 + x$, and I want to express that in terms of a sum of other polynomials how may I do that in Mathematica? Specifically I would like to say that $$p(x) = \...
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1answer
35 views

How to check if 0 polynomial lies in span of some polynomials?

I have lot of polynomials like this ...
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1answer
39 views

How to create a correct density plot from “NDSolve” solution?

I would like to create the projection of a solution in plane from the differential equation set solution. However, the way I did it is not as I would like it, it does not have a smoothness. Here's ...
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1answer
40 views

How to generate a list (or even a sequence or a string) containing {x[1]==0&&x[2]==0&&…&&x[10]==0?

I need to solve a bunch of systems of n equations in n unknowns where n varies. I can do ...
4
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1answer
54 views

How to nest multiple functions with multiple variables

I'm trying to solve coupled equations by using iteration. There are two functions $G$ and $H$ that I need to find. In the code, G and H are actually lists of numbers. I start by using a simpler ...
0
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1answer
41 views

Reversing the flow of the equation sign. Compacting an equation. Choosing which variables to show

Here's a simple example of what I'm trying to get at with that mysterious title. I start off with a Hermitian matrix that I derived analytically ...
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0answers
70 views

Solving system of equations with Summation

I have these three equations (eq1, eq2, eq3): ...
1
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1answer
48 views

How to solve this ODE by DSolve or NDSolve?

I try to solve this second order ODE to get k: $ \frac { \partial }{\partial z} ~ \frac{ \partial } {\partial \bar{z}}~ k[z, \bar{z}] = 5 $ Where z is complex coordinates, so to take the ...
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0answers
48 views

Second order differential equation not getting solved using DSolve

I am trying to solve this second order differential equation $-\frac{k T}{q n(x)} \frac{d^2n(x)}{dx^2} + \frac{k T}{q (n(x))^2} (\frac{d n(x)}{dx})^2 = \frac{q}{\epsilon} (N_D(x) - n(x))$. So I want ...
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0answers
26 views

Solving numerically a dissipative non-linear system of coupled ODEs [duplicate]

My problem is to integrate a set of couple non-linear and first order ODEs. They are Eqs. (45) -- (50) in the paper https://arxiv.org/pdf/1901.03380.pdf. This is the set of differential equations I ...
3
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4answers
135 views

The difference of Prime in Solve doesn't work

Can someone explain why Solve does not work with Prime difference? This cond does not work: Solve[Prime[n] - Prime[m] == 8, {n, m}, Integers] But you can find ...
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2answers
48 views

Can't solve for y in a fairly simple work done by magnetic field equation

The equations below are essentially calculations for a railgun-type mechanism (here is a good image description). I also drew an image using my own variables as definitions: I assumed that ...
1
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1answer
50 views

Hybrid ODE simulation with very small parameters

I am trying to solve a Hybrid dynamical system using NDSolve and WhenEvent. I am able to simulate when the parameters are close ...
4
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3answers
211 views

Writing a program that will filter the integer solutions

I've the following equation: b==(-12 + Sqrt[3] Sqrt[ 3 (-4 + r)^2 + 12 a^2 (-2 + r) - 4 a (-5 + r) (-2 + r) + 4 a^3 (-2 + r)^2] + 3 r)/(6 (-2 + r)) ...