Questions tagged [equation-solving]
Questions on the analytic and numerical equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).
1
vote
0answers
23 views
Normal form for Hopf bifurcation
I'm trying to obtain the normal form for the Hopf bifurcation using mathematica. I was looking at the following article:
downloads.hindawi.com/journals/sv/1995/581272.pdf
and I´ve tried to solve (25)...
0
votes
0answers
67 views
DSolve for ODEs with terms like $ y^2(t) $
Mathematica does not give me any solution for the ODEs as follows:
...
1
vote
0answers
56 views
Finding root of symbolic function
I'm trying to find a root of the following equation
$$\theta^\frac{t}{s}-\theta-\sqrt{1-p},$$
where $0<t\leq1\leq s$ and $0<p<1$.
I've tried FindRoot and Reduce, but somehow they don't ...
9
votes
3answers
1k views
Can this be solved even faster?
So I would like to solve the following set of equation for $m_i$ given a set of ${M_m,N_m}$.
$$
m_1 +m_2 +m_3 +m_4 =M_m \\
|m_1| +|m_2| +|m_3| +|m_4| =N_m
$$
All variables are integers.
Also $N_m \...
2
votes
1answer
87 views
Finding all roots to equation [duplicate]
I'm currently doing some Mathematica exercises, and I'm stuck on this one task where you're supposed to plot the functions h(t)= |3-t^2|+|t-1|-t^2 , g(t)=3sin(t)
in the same grap, and then find all ...
4
votes
2answers
76 views
Why Can't Mathematica Resolve this Simple Quantified Expression?
I've been using Mathematica as a hobbyist, off and on, for some time. So while I'm by no means an expert I've used it long enough to know that what might seem obvious to me is not necessarily obvious ...
0
votes
0answers
44 views
Nominal problem with Solve, Reduce, FindRoot out
I try to solve the following system but I had the error message.
...
1
vote
4answers
127 views
How to generate repetitive graphs?
I need to create several graph for different values of a parameter $h$.
The code is the following
...
1
vote
1answer
99 views
Solving the eigenvalue problem for a double well potential using a 1D particle in a box as a basis set
My first question is how would I go about getting the 1D particle in a box eigenfunctions using matrix techniques and how would I use the particle in a box eigenfunctions as a basis set for the ...
0
votes
1answer
46 views
Trying to obtain a numeric solution to an inequality. Code might be not working as intended
I need to check whether an inequality can have solutions in the real numbers, given some extra constraints on the variables. I suspect that no solutions exist but I would like some verification of ...
0
votes
0answers
38 views
I need FindRoot with pure numerical Secant method [on hold]
When I use FindRoot "Secant" method like this:
FindRoot[
{MyComplexFunctionCallingPartOfAnArray[a] == 0, a > 0},
{a, 1, 20},
Method -> "Secant"
]
I got ...
-2
votes
2answers
57 views
Non Linear Equation Solve [on hold]
a = 1/Pi ((t/2 - 1)*ArcCos[1 - 2/t] + (-1 + 4/(3 t) - 4/(3 t^2)) Sqrt[t - 1]);
Solve[-0.5 - a == 0, t]
There is a way to solve this non linear equation??
Thanx
0
votes
1answer
49 views
How to introduce a NSolve into a ContourPlot?
I have an equation that I want to solve, and I'm using DensityPlot, as I was told here NSolve two unknowns $ r, x $ in order to have a curve $ r(x) $ .
Meaning I have a relation $f(r,x)=0$, and with ...
0
votes
0answers
27 views
Problems with NDSolve, have a problem of reducing Numerical errors
I am trying solve differential equation subject to boundary condition. Here is my code:
...
0
votes
3answers
44 views
NSolve two unknowns $ r, x $ in order to have a curve $ r(x) $
I'm trying to solve :
NSolve[3 r Sqrt[x/(1 - x)] + 1/2 r^3 (x/(1 - x))^(3/2) - (
3 r x Csch[r Sqrt[x/(1 - x)]])/(1 - x) == 0, {x, 0.5, 1}, {r, 0,
5}]
My goal ...
0
votes
1answer
32 views
NSolve cannot work with MinValue?
I am trying to solve the following problem: find the smallest value of $b$ such that the inverse of the solution u[p] given by ...
2
votes
2answers
180 views
Help for Solving Two Equations For Two Unknows (from a Paper)
I am trying to reproduce numerically the results found in this paper: https://ieeexplore.ieee.org/document/1707778
You don't necessarily need to read it. Basically I boils down to solving a two ...
1
vote
2answers
37 views
Storing values of NDSolve or NIntegrate
I am looking in plotting some solutions of NDSolve or NIntegrate but they take too much time to run, thus it is not handy if I ...
0
votes
0answers
18 views
Find value of expression based on variable equality instead of assignment
I have certain relations or equalities which determine how different variables are related to each other. These relations are meant to be used to further calculate the value of some other expression.
...
2
votes
2answers
63 views
Plotting solution to Differential Equation with separable variables
Got this differential equation $$y'=\frac{-x^2(y+1)}{y^2(x-1)}$$
If I try directly to DSolve it
...
5
votes
2answers
105 views
Symbolic solution for the energy of potential flow
I have a question to a physical task in Mathematica.
We have this equation of motion:
$$m\cdot\ddot{x} = -m(\omega_0^2\cdot x+(\epsilon x^3))=-\frac{d}{dx}V(x)$$
For energy of masspoint there is ...
0
votes
2answers
59 views
Question about imaginary number in solution of equation
I want to solve the below eqution:
Solve[2*t^3 + t^2 - \[Theta]*t - 2*\[Theta] == 0, t]
I get three roots of this eqution and I guess that two are imaginary and ...
0
votes
2answers
70 views
I want to erase the error
Error message does not disappear.
I can not solve the same number of solve expression and variable.
Please tell me some advice.
...
0
votes
1answer
33 views
Plot[] fails to show all results of Solve[]
I'm interested in the intersection points of two functions: $y=r+x$, where $r$ is the constant, and $y=ln(1+x)$. The following code plots the two intersection points for different (negative values) of ...
2
votes
1answer
74 views
Solve returns solution that isn't (always) one
I was asking Mathematica to find the roots of $f(x) = a+\sqrt{x^2-b}$ and it returns $x = \pm \sqrt{a^2+b}$. These are however solutions only if $a\leq 0$ (there are no roots if a is positive since ...
0
votes
3answers
80 views
Question about equation solving [on hold]
I want to solve the equation and use the code below.
Solve[2*t^3 + t^2 - θ*t - 2*θ == 0, t]
Then, I get three roots of it. Here, I guess two roots are imaginary ...
0
votes
1answer
48 views
1
vote
2answers
38 views
FullSimplify applied to equations: not simplifying though apparently it should
I tried to Fullsimplify
$$ e^x(1-x)=0$$
to the equation
$$1-x=0$$
However the command
FullSimplify[E^x (1 - x) == 0]
just ...
1
vote
3answers
82 views
ndsolve with multiple initial conditions
I am trying to solve a PDE using the NDsolve with initial and boundary conditions,
...
0
votes
4answers
106 views
How to solve equation in integer numbers
I would like to solve an equation like this $\frac{\log(2)}{\log(3)}=\frac{n-0.5}{k-0.5}$ where $n$, $k$ are positive integers and $\log$ is natural logarithm. Of course, I can do only numerical ...
0
votes
0answers
31 views
Find a matrix that are unitarily equal to the given matrix
I have four $5\times 5$ matrices, $P_i, Q_i$ ($i=1, 2$) as follows:
$P_1=\begin{pmatrix}
1 & 0 & 0 & 0 & 0 \\
0 & 1 & 0 & 0 & 0 \\
0 & 0 & 0 & 0 & -...
1
vote
1answer
79 views
ODE which can be solved without parametrisation
I want to solve the following differential equation, which can be solved without parametrisation
$\qquad y^2y'^2-2xyy'=x^2-2y^2$
I need the solution for my student research project.
When I try to ...
1
vote
1answer
60 views
Find (guess) an integral curver
I consider the following system
$$
\begin{cases}
x'=-x^2 + 3 x - 2 x y=:f(x,y)\\
y'=y^2 - 2 y + x y:=g(x,y)
\end{cases}
$$
It has a fixed point at $(1,1)$ and the linearization there has a centre,...
4
votes
2answers
74 views
RSolve not reducing for a certain recurrence relation
I'm trying to use RSolve as follows to solve a recurrence relation:
...
0
votes
1answer
31 views
Vectorise NSolve
I am very new to Mathematica.
What I am trying to do is the following.
I have a two-dimensional surface which depends on an additional parameter.
I would like to plot the locus of the saddle points, ...
0
votes
1answer
64 views
Finding the root of a Transcendental equation [closed]
I'm trying to find R in the transcendental equation.
$R + u_r\,t=(\frac{a_1\,B}{\nu}\, \gamma_0^2)^{\frac{3}{4}} \sigma R \,e^{\frac{3 \sigma}{v_{sh}\,t_{acc}}(R-R^*)}$
Everything except R is a ...
0
votes
0answers
68 views
2
votes
2answers
141 views
Large overdetermined system of quadratic equations
Could anyone help to solve the system of 81 quadratic equations with 27 variables? The system has solutions. Constraint:
$\sum_{i=0}^{26} x^2_i=1$
$-x_1 x_3-x_2 x_6+x_1 x_9+x_2 x_{18}=0$
$-x_1 x_4-...
0
votes
1answer
27 views
Solve and a system of equations with a parameter
I've been struggling with this a bit. I've been googling in search for an answer but failed to do so.
I want to solve this system of equations with a parameter
...
0
votes
1answer
35 views
Plotting a=f(b) and b=g(a) on the (a,b) plane when neither has a closed solution
I've searched for a solution but haven't found one yet, but this is possibly an easy fix - I'm new to Mathematica.
I have two functions, each with $(a,b)$ as arguments and both with no closed form ...
1
vote
1answer
41 views
Performing a FindRoot from Numerical integration
I am trying to evaluate:
FindRoot[Xfnew[γ, w, Hi, mx]*92*10^23*γ^(4/(1 + w)) == 1198/10000, {Hi, hs},
MaxIterations -> 10000]
for some starting value hs,...
2
votes
1answer
58 views
Why is Reduce in Mathematica giving solution in other symbols that don't exist in original equation [closed]
Here is an example:
Reduce[P/Q < (P - X)/(Q - X) && X > 0 && P > 0 && Q > 0 && P > Q, {X}, Integers]
The solution ...
0
votes
0answers
41 views
DSolve inverse function
I trying to solve a differential equation
DSolve[{D[r[a], a] == 3 r[a]/a (w - (g *(1 + w)*(1 + r[a]))/(1 + g*r[a])),r[1] == r0}, r, a]
But the solution is a ...
0
votes
0answers
47 views
problem to solve a non linear equation
variable[[i]]-(1/Pi)((t/2 - 1)*(Pi-2Sqrt[t-1]+2/3(t-1)^(3/2))+(-1+4/(3t)+4/(3t^2))Sqrt[(t-1)])==0
This is the equation but the problem is that the solution is ...
1
vote
3answers
76 views
0
votes
0answers
29 views
Manipulating Equations: Substracting two equations
I was wondering why I fail to substract two equations using thread, while it works properly, as described here for additions.
Example: Let a system of equations be given:
...
1
vote
1answer
68 views
How to transform a FindRoot in a NDSolve?
some days ago I did a question about a problem with a findroot.
The solution was to convert the FindRoot in a "fake" NDSolve.
How can I do the same if the FindRoot has more equation ?
I make here an ...
1
vote
2answers
100 views
1
vote
1answer
37 views
Reducing system of 10 inequalities
I have the following system of inequalities of real variables
...
2
votes
1answer
73 views
How to automate this solution?
The Mathematica solver is strong. Of course, there is a room to improve it. Here is an example. The command
...
