Questions tagged [equation-solving]
Questions on the analytic and numerical equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).
1
vote
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 ...
1
vote
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 ...
0
votes
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
vote
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
votes
1answer
91 views
How to solve this 2nd-order ODE with quadratic coefficients?
Consider an ODE eigensystem
$$
\begin{bmatrix}
0 & d_1-\mathrm id_2 \\
d_1+\mathrm id_2 & 0
\end{bmatrix}
\begin{bmatrix} a(y) \\ b(y) \end{bmatrix} = \lambda \begin{bmatrix} a(y) \\ b(...
0
votes
0answers
71 views
Solving a differo-integral equation [duplicate]
I've the following equation for x(t):
$$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{...
0
votes
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
vote
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 ...
0
votes
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 ...
3
votes
2answers
141 views
0
votes
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 ...
0
votes
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? ...
1
vote
2answers
103 views
Multivariate Newton-Raphson method and FindRoot module [on hold]
Let's suppose that we have the following equation
...
1
vote
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
votes
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
votes
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, $$\...
0
votes
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'
...
0
votes
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
votes
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 ...
1
vote
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
votes
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
votes
1answer
136 views
why this PDE causes internal 1/0 division?
Assigned WRI Case number 4210941
Using 11.3 on widnows 10, this input
...
0
votes
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
votes
1answer
136 views
Mathematica and IBVP mixing temporal and spatial derivatives
The following PDE's-system-solving code
...
1
vote
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
votes
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
votes
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
votes
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
votes
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
votes
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
votes
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.
...
0
votes
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
votes
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
votes
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$.
...
0
votes
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
votes
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
vote
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]$$
without success, I tried to get a specific numeric solution
...
1
vote
0answers
44 views
How to preserve braces in result
I have a result from equation, for example
p={{0<=x<=1/5||x==9/10},{0<=x<=1/5||x==9/10}}
and using
Cases[p, z_?NumericQ -> z, Infinity]
I get
{0,1/5,9/10,0,1/5,9/10}
But I ...
1
vote
2answers
109 views
5
votes
3answers
113 views
Duplicate solutions in NSolve
In v11.3 NSolve returns a bunch of redundant solutions for the following set of six equations:
...
0
votes
2answers
38 views
Get the set of points from constant function
I have a function f defined by points:
finput = {{0, 1/5}, {1/5, 1/5}, {1/2, 1}, {1, 0}};
ListLinePlot[finput, PlotRange -> {{0, 1}, {0, 1}}]
Then I create a ...
5
votes
3answers
409 views
Find position without iterating
The code below solves for the four value of $m_i$ for a given pair of $(N_m,M_m)$.
where
$$
m_1+m_2+m_3+m_4 = M_m\\
|m_1|+|m_2|+|m_3|+|m_4| = N_m
$$
Edit 2
New Sorting
I have now realised that the ...
0
votes
1answer
56 views
Solving systems (?) of equations [closed]
I've been working on my school project. I'm new to Mathematica. This is a part of my Physics demonstration, I want my program to do something until tmax. Where tmax is the positive and real solution ...
2
votes
2answers
75 views
How to get solve to produce an answer if there are irrelevant equations?
Suppose I have a set of relations which I'd like to store as one variable.
setOfRelations = {x - y == 0, z - w == 0}
If I wish to obtain ...
1
vote
2answers
158 views
A numerical boundary conditions paradox
For $(t,z)\in[0,1]\times[-1,0]$
zmin = -1; tmax = 1;
and some fields $w(t,z)$ and $y(t,z)$
...
0
votes
1answer
27 views
Solving an equation involving a determinant (including spherical recursive functions)does not compute
I'm trying to solve this matrix to get a resulting function that depends on the variable Q (or if impossible, H3).
When I try to to that I get two results: if I try to solve for Q, it doesn't show ...
1
vote
1answer
33 views
Find Transformation Matrix for Vectors of Functions, and Restrict Results of Solve Function
I have two vectors v,w which have a rather simple linear transformation A.v=w. My goal is to obtain ...
0
votes
1answer
70 views
Solve integer linear system [closed]
I want to find a solution of the system
$$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
votes
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 ...
0
votes
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. ...
