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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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1answer
9 views

What is wrong with my syntax when trying to solve the following system?

Why doesn't Mathematica return $k=1$ for the following system of equations? Solve[{x + (k + 1) y - 3 + k == 0, x + 2y - 2 == 0}, k] But, instead, it gives an ...
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1answer
26 views

Solving for the roots of a huge polynomial with NSolve

I am new to Mathematica. I thought it was going to be the solution to all my problems. I very naively tried feeding a huge complex polynomial with exponential parts to ...
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1answer
73 views

How to resolve the fail when applying a user-defined solver?

The user-defined function pdetoode and pdetoae, developed by @xzczd, is very useful to deal with a PDE system when there is ...
1
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1answer
91 views

Interpreting Mathematica code on black holes

I am trying to understand the code written down on page 7 of this document (code is in Mathematica) I understand pretty much all of the code on the previous page needed to setup the page 7 code (...
2
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1answer
91 views

How to solve this 2nd-order ODE with quadratic coefficients?

Consider an ODE eigensystem $$ \begin{bmatrix} 0 & d_1-\mathrm id_2 \\ d_1+\mathrm id_2 & 0 \end{bmatrix} \begin{bmatrix} a(y) \\ b(y) \end{bmatrix} = \lambda \begin{bmatrix} a(y) \\ b(...
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0answers
71 views

Solving a differo-integral equation [duplicate]

I've the following equation for x(t): $$x'(t)\cdot\text{a}+\text{b}\cdot\frac{x'(t)}{x(t)+\text{c}}+\frac{\partial}{\partial t}\left\{\int_0^tx(\tau)\cdot\mathcal{...
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2answers
66 views

When computation takes a long time, how to find out if this is normal or if my script contains an error?

I study mechanical engineering and I' working on my first bigger project on Mathematica right now. It's a multibody problem that leads to a system of 4 large equations I'm supposed to solve ...
1
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1answer
52 views

Singularities forming on boundary while solving system of pde's

This is a follow up of a previous question I asked regarding solving a system of coupled, non-linear partial differential equations, 2D spatially + time. The equations (shown below) model a magnetic ...
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3answers
44 views

How to get the Roots of nonlinear equations

How to get the Roots of nonlinear equations. nu=326.531 Plot[(I*m1)*Tanh[I*m1] - nu, {m1, -1, 30}] How to get the first ten positive roots and i have tried ...
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2answers
141 views

Solution or artifact?

I am trying to increase the precision of the code ...
0
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2answers
66 views

Correct interpretation of an ODE solution

I am not very good with Mathematica but I am trying to solve the following initial value problem $y''(t)=\lambda_1 y'(t)e^{y(t)}+ \lambda_2 y'(t)e^{-y(t)},$ $ y(0)=0$ I have tried first the ...
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1answer
54 views

Problem with Resolve

The question is: for which values of the parameter $a$ the equations $$4^{x+1}-3\ 2^{x+3}=2^{x+4}-64 $$ and $$(a+30) \left(-9^x\right)+3^{x+4}+27^x=a \left(81-10\ 3^{x+1}\right) $$ are equivalent? ...
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2answers
103 views

Multivariate Newton-Raphson method and FindRoot module [on hold]

Let's suppose that we have the following equation ...
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0answers
48 views

Why the solution is having a negative value, it should be positive as it is a physical quantity

I want to solve 5 non-linear equations simultaneously, so I am using Solve[] function. Here is my code: ...
0
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1answer
46 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 ...
3
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2answers
157 views

Eigen values of a third order linear homogenous ODE

From a system of PDEs where i used the following ansatz: $$\theta_w(x,y) = e^{-\beta_h x} f(x) e^{-\beta_c y} g(y)$$. $F(x) := \int f(x) \, \mathrm{d}x$ and $G(y) := \int g(y) \, \mathrm{d}y$ So, $$\...
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1answer
68 views

What is going wrong when I try to solve a simple linear equation? [closed]

I'm trying to understand how does the LinearSolve function works. I'm trying it out like this: A' ...
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0answers
39 views

How to solve a system of two equations and two variables in function of others terms

I want to Find C1 and C2 in terms of a and e from the following system of equations: ...
4
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1answer
52 views

Computing the seven roots of a polynomial

This question was originally asked by @fsrong70 six months ago. The OP deleted it shortly after posting and has not returned to this site since. I had just figured it out when it was deleted. I ...
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2answers
47 views

Finding a solution to an equation and plotting it

I have this equation that I want solve explicitly so that $\omega$ is dependent of $k$ like this $\omega (k)$ and then plot it on a plane for k, but I have no idea which function to use. This is the ...
0
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2answers
33 views

How to use reduce to solve this equation?

I have this simple equation to solve (1 == 62.5*E^(-30*10^6/x), {x}), and Mathematica is able to give a correct answer. However, there is this warning message () I don't understand, can anyone ...
4
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1answer
136 views

why this PDE causes internal 1/0 division?

Assigned WRI Case number 4210941 Using 11.3 on widnows 10, this input ...
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1answer
39 views

Why doesn't Solve work unless I request a solution for both unknowns?

I have two circuit equations power == voltage*current voltage == resistance*current You can plug the second equation into the first and get ...
3
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1answer
136 views
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2answers
38 views

How to reduce the residue in NSolve for a system of 3 non-linear equations

I have written the following snippet in Mathematica to solve a system of 3 non-linear equations? ...
0
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1answer
43 views

FindRoot and symbolic evaluation

Following the Symbolic evaluation documentation, I am trying to solve the equation: $y'(x) = a*y(x), \quad y(0)=1$ where I later fix a via FindRoot, requiring that $y(2) = 2$: ...
6
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1answer
110 views

Solving a system of coupled non-linear partial differential equations

I am trying to solve a system of coupled non-linear partial differential equations, 2D spatially + time. The equations are: where c, d, and p are constants. I am solving for the functions Az and Bz ...
3
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1answer
98 views

Solving for Euler Angles

I would like to determine Euler angles according to the following example. My example: I have the three vectors in an original set of axes: ...
15
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2answers
462 views

Possible bug in Solve function?

Bug introduced in 10.0 and persisting through 11.3 or later In 11.3.0 for Microsoft Windows (64-bit) (March 7, 2018) writing: ...
0
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1answer
31 views

Solving an equation

I need to solve the following equation (expr = 0) for "A", but looks like Solve and Reduce struggle. All parameters are positive, and "expr" is given below. (I suspect the issue might be due to powers ...
0
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1answer
66 views

Simplify DSolve solution with products of square roots

The following code solves a simple 2nd-order linear differential equation with all real parameters. ...
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0answers
37 views

Solving Equation from 3rd degree with unknown coefficients

I Try to get the simplest real root for the following equation but I failed ...
0
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1answer
50 views

Solve a system by Cramer's rule using loop

Consider the linear system AX=B,where A={{3, 0, 2}, {-3, 2, 2}, {2, -3, 3}},B={{3}, {-1}, {4}} and x=...
3
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3answers
86 views

DSolve returns incorrect solution by automatically assuming positive parameters?

The following code solves a simple 2nd-order linear ODE with real parameters $a,b$. ...
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1answer
78 views

Why can't solve this equation, why there is no answer [closed]

Why can't solve this equation, why there is no answer. Please give me advice if you can understand, ...
0
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1answer
48 views

Solving system of equations for coordinates

This is my first time here, so let me know if there's something I need to add to the post etc. Anyway, I need some help with Mathematica and linear algebra, and I got some tips that this would be the ...
1
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2answers
67 views

NSolve does not work

I want to solve this eq' $$((1 - t) r)/(1 - x) = \log[\exp[(r t )/x] + 1 - \exp[r]$$ without success, I tried to get a specific numeric solution ...
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0answers
44 views

How to preserve braces in result

I have a result from equation, for example p={{0<=x<=1/5||x==9/10},{0<=x<=1/5||x==9/10}} and using Cases[p, z_?NumericQ -> z, Infinity] I get {0,1/5,9/10,0,1/5,9/10} But I ...
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2answers
109 views

A problem with FindRoot

I have the following ...
5
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3answers
113 views

Duplicate solutions in NSolve

In v11.3 NSolve returns a bunch of redundant solutions for the following set of six equations: ...
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2answers
38 views

Get the set of points from constant function

I have a function f defined by points: finput = {{0, 1/5}, {1/5, 1/5}, {1/2, 1}, {1, 0}}; ListLinePlot[finput, PlotRange -> {{0, 1}, {0, 1}}] Then I create a ...
5
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3answers
409 views

Find position without iterating

The code below solves for the four value of $m_i$ for a given pair of $(N_m,M_m)$. where $$ m_1+m_2+m_3+m_4 = M_m\\ |m_1|+|m_2|+|m_3|+|m_4| = N_m $$ Edit 2 New Sorting I have now realised that the ...
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1answer
56 views

Solving systems (?) of equations [closed]

I've been working on my school project. I'm new to Mathematica. This is a part of my Physics demonstration, I want my program to do something until tmax. Where tmax is the positive and real solution ...
2
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2answers
75 views

How to get solve to produce an answer if there are irrelevant equations?

Suppose I have a set of relations which I'd like to store as one variable. setOfRelations = {x - y == 0, z - w == 0} If I wish to obtain ...
1
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2answers
158 views

A numerical boundary conditions paradox

For $(t,z)\in[0,1]\times[-1,0]$ zmin = -1; tmax = 1; and some fields $w(t,z)$ and $y(t,z)$ ...
0
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1answer
27 views

Solving an equation involving a determinant (including spherical recursive functions)does not compute

I'm trying to solve this matrix to get a resulting function that depends on the variable Q (or if impossible, H3). When I try to to that I get two results: if I try to solve for Q, it doesn't show ...
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1answer
33 views

Find Transformation Matrix for Vectors of Functions, and Restrict Results of Solve Function

I have two vectors v,w which have a rather simple linear transformation A.v=w. My goal is to obtain ...
0
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1answer
70 views

Solve integer linear system [closed]

I want to find a solution of the system $$A x = 0,\quad x>0,\ x\in\mathbb{Z}^d$$ where the matrix $A$ has integer entries. With a single solution I am happy. There is a way to do this? If not, can ...
0
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3answers
89 views

How to solve this hyperbolic trig equation iteratively?

i need the "a" value from this solver and it isnt working. i know a should be between 0 and 5, most likely around 1. The other values im not as sure of but y20 and y10 should be negative numbers ...
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0answers
18 views

Cant get my solve function to run [duplicate]

Solve function on mathematica not working. I'm doing a large solve function with several hyperbolic trig functions inside, and it just runs forever. Ive let it sit for a day and it still didnt run. ...