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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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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)...
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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
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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
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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
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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
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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 ...
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0answers
44 views

Nominal problem with Solve, Reduce, FindRoot out

I try to solve the following system but I had the error message. ...
1
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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
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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
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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
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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
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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 ...
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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
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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
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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
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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
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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
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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
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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
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1answer
48 views
1
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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
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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
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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
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0answers
68 views

An optimization problem

I have the following two quantities denoted by $LHS$ and $RHS$: ...
2
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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
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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
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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 ...
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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
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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 ...
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2answers
100 views
1
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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 ...