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
67 views

Is it possible to use FindRoot with a function of two variables? [closed]

How can I use FindRoot with 2 variables function? Is there a different way to do that? For example ...
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1answer
36 views

Conditions to make unitary a given matrix

Suppose I have some symmetric matrix W = {{c[1, 1], c[1, 2], c[1, 3]}, {c[1, 2], c[2, 2],c[2, 3]}, {c[1, 3], c[2, 3], c[3, 3]}}; where the c's are complex and I ...
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1answer
44 views

Finding closed forms for various addition laws on elliptic curves, FullSimplify fails even with assumptions?

I would like to get Mathematica to do some tedious algebra for me, but I have been unsuccessful so far, and I don't know whether I am not using it correctly or whether it is simply not sophisticated ...
1
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1answer
172 views

How do you avoid Null in matrix? [closed]

The following matrix equation is a Lyapunov equation, $$ mA.x+ x.mA^T=-mC,$$ the matrix $mA$ is given by $$ ...
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2answers
266 views

Find multiple solutions of a nonlinear ODE

I have a nonlinear ordinary differential equation with two parameters c and R in the form of: ...
1
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1answer
57 views

Numerical solution of equation with free parameters

I have an equation which is not analytically solvable, thus I need to solve it numerically. But, this equation has some free parameters which I want to replace them with some numbers after solving the ...
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1answer
43 views

Reducing or solving a simple linear equation problem

I have the following equations ...
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0answers
51 views

The Solve command is not able to find a solution of a system

I have a system with large rational numbers ...
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1answer
42 views
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1answer
31 views

FindRoot with NIntegrate: either recursion depth exceeded or numerical integration converging too slowly

Trying to numerically solve an equation involving an integral, either the error Recursion depth exceeded appears (when ...
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1answer
33 views

How does Mathematica solve this 2D piecewise function from constraints?

I am interested in learning the technique(s) used to solve the following 2D piecewise equation for $x, y$ when given $z$, where $z = f(x, y)$. $\text{Given that $x \in \mathbb{Z}$, $y \in \mathbb{Z}$}...
4
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1answer
155 views

Solving partial differential equation involving Hilbert transform

While solving one research paper published in Physical Review Letters, I came across the following equation and I am unable to solve it. $$\frac{\partial f}{\partial t}−(\mathcal{H}(f)\left(\frac{\...
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1answer
66 views

Problems with manipulation

I am plotting geodesics on an ellipsoid. My problem is that I cannot do the manipulation, from a, b, c. From the starting point and the initial vector, the manipulation works well, but from the ...
1
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1answer
65 views

ListPlot3D of the results of FindRoot

I have a system of 2 simultaneous equations where i want to calculate the values of Tc and Tc which ranging with the values of two variables which are wfc and V. I tried to evaluate it by using ...
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0answers
67 views

Limiting solution space for symbolic algebra problems

I have a system of 12 quadratic equations with 12 variables (x11, x12, x21, x22, x23, x33, p1, p2, p3, ϕ, μ, τ) and several positive constants,w, q1, q2. ... > 0<...
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2answers
71 views

Vortex motion equation for flux-flow instability

I am solving the motion equation of an isolated vortex oscillation in a superconductor. I am assuming that the driving force is generated by an RF current oscillating at 1.3 GHz. The main point of ...
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2answers
104 views

Error messages for FindRoot and NIntegrate

I want to solve the following problem. First, the setup. A function $V(\varphi)$ defined as \begin{multline} V(\varphi)=\frac{\alpha-3}{4}e^{\sqrt{2\alpha}\varphi}+\frac{\alpha-5} {\gamma}e^{(\...
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2answers
39 views

NSolve cannot find solution to system of trig equations

I was making a program to convert a rotation matrix to a set of euler angles. I wanted to do this for any valid rotation order that the euler angles were made with, and I did not want to do it the ...
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1answer
58 views

Five equations to solve 6-variables question, is it possible?

I was given a task to find the value of variable a,b,c,d,e and f. But I'm not sure it is even possible, given that only 5 equations are available. Can anybody point out how to solve these: ...
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1answer
66 views

Still having problem with solving high polynomials with exponential equations simultaneously

I need to find the value of Ta and Tc for two simultaneous equations to get a numerical answer using NSolve. I have tried using FindMinimum and NMinimize and still could not solve the problem. Here is ...
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1answer
51 views

Why does Mathematica just return Hold of my Input? [closed]

Example: Solve[x^2 + a x + 1 == 0, x] Output: Hold[Solve[x^2 + a x + 1 == 0, x]] What is the problem? Any child can solve this in its head
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2answers
124 views

Solving BPV of second order nonlinear ODE through NDSolve

I'm trying to solve a 2nd order related ODE system in two region using Piecewise. BC: 1) y'[0]=0 and at y'[1.6]=0 while at 1 <...
13
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1answer
3k views

Has Mathematica 12 gotten worse at solving simple equations?

Mathematica used to be easily able to solve an equation like this: Reduce[Log[Sqrt[k p]/Log[k]] == 0, p] (I can easily do it myself, at least I can find the ...
4
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1answer
93 views

Triggering WhenEvent as a result of WhenEvent

I'm attempting to solve a dead-simple differential equation with events: ...
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0answers
53 views

Discontinuity in plotting the solution of a trig function system

I have the following system ...
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0answers
34 views

Solving equations, checking linear dependency of equations

I have the following input and try to do solve the equations for in total four unknowns. When I run the input only "solutions" for two of the four unknowns are given in the output. I am not quite sure,...
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1answer
80 views

Can not solve this question [closed]

Solve[beta*x *((1 + (1 - m)*sigma*theta ((x^(-1/2) - 1)/((1 - theta)*x^(-1/2) + theta)))) - S == 0, x] Can someone please help me, I don't know why x is not ...
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1answer
35 views

How do I plot the output of Solve as a function? [closed]

I have a system of equations (13 eq) and I want to solve for S. There are four solutions in terms of k and ...
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3answers
111 views

Tangent point coordinates when the curve is a set of points

I want to find the coordinates of the tangent point between a convex curve and a line that passes from a point with known coordinates (0,b) ("efficient portfolio" ...
3
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1answer
66 views

Help with solving a PDE and plotting its solution

I have trouble with solving the PDE with periodic boundary condition, which appears to be stiff somewhere, so I tried "StiffnessSwitching". But the code still doesn'...
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1answer
31 views

Plotting roots of a non polynomial function

I'd like to plot the solutions of a function f(y)=k, when f(y) is non polynomial. This is the Mathematica script I have produced so far: ...
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1answer
58 views

Coupled PDEs: Wave and String Equations

I need to solve a system of mixed string and wave equations. Omitting some constants it looks like this: $$u_ {\text {yy}} (y, t) - u_ {\text {tt}} (y, t) = \varphi _{t}(x, y, t)$$ $$\nabla _{\{x,y\}}...
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2answers
64 views

Numerical equation solving with FindRoot and BandpassFilter

I have problems combining filtering of a data list and FindRoot. Here is an example: ...
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0answers
62 views

Solve a Differential equation analytically instead of numerically

I want to solve the differential equations (shown below in the list 'eqs') analytically instead of numerical. Using NDSolve the following code works perfectly fine but using DSolve it doensn't. I ...
4
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2answers
137 views

Approximate solutions to non polynomial equations

Let's assume the following symbolic equations $$E=\sqrt{p^2+m^2}+\frac{e d_1(p)}{r}+\frac{e^2d_2(p)}{r^2}$$ being $d_{i}$ some generic function of $p$. I would like to find solutions to this ...
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0answers
48 views

Problem with a plot

I have a function which has a dependency on x alone. I wanted to find the roots of this equation, so I tried plotting the equation, but I am getting the error "integer expected at position 2 in Surd[0....
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2answers
119 views

Mathematica unable to interpret equations in DSolve

I'm trying to solve a system of seven ODEs with seven conditions. Since the following approach using DSolve is yielding the same output as the input, Mathematica can't find a solution. ...
4
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1answer
84 views

Hat function(UnitTriangle[x]) is really applicable in Finite Element Method?

I am learning finite element method(galerkin method) for solving ode/pde. when searching this topic, I often see examples using the hat functionUnitTriangle[x] as ...
2
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1answer
83 views

Simultaneous Equations and Optimization

I have the following simultaneous equations. $W=G[V](s+80)+(1-G[V])114$ $V=(1-F[W])(90-s)$ where $F$ and $G$ are cumulative distribution functions of $x$ and $y$. The variables of $x$ and $y$ are ...
-1
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1answer
49 views

Assigning a general result from Solve to a variable [closed]

Thank you Michel, for the help. Now, I want to get the result and assign it to a variable and then make a new function. How can I do that? I was tryng this way with "First", as follow the picture, ...
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2answers
92 views

Solving equation with Curl in angular velocity

In 3 dimensions, angular velocity is given as: $$\boldsymbol{\omega} = \frac{1}{2} \nabla \times \boldsymbol{v}$$ How can I use mathematica to solve for velocity $\boldsymbol{v}$, if I give a value ...
2
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1answer
65 views

Problem with RSolve function

When I use RSolve to solve the recurrence: $S(n)=\dfrac{1}{-S(n-1)-2},S(1)=-2/3$, it gives an empty solution: however the solution should be:$S(n)=-\dfrac{n+1}{n+2}$ Did I do something wrong?
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1answer
53 views

Area of a parametric plot with interpolating functions

I am looking for the area of a parametric plot defined by two solutions (defined as: VVLt & PVLt) of Numerically solved differential equations. The problem is when i'm trying to integrate the two, ...
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0answers
31 views

Bounding Solve results to named variables

How can i bound results of my Solve function to variables properly? This metod works but causes unexpected troubles i struggle to resolve ...
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1answer
68 views

How to find the largest degree of a polynomial?

I have a huge polynomial, and I am having the following issues 1. I wanted to find the largest and smallest degree of that polynomial. 2. How to truncate the lower order terms, sometimes higher order ...
0
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1answer
101 views

Solving polynomials and exponential simultaneously

I am trying to solve two equations simultaneously in Mathematica. The LHS has a high polynomials whereas the RHS has an exponential functions. It does not have to be exact solution, tolerance is ...
2
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2answers
79 views

Solving for three parameters from a matrix equation and storing them in separate variables

Say I have a matrix $$ Z=\begin{pmatrix}-\frac{1}{\sqrt 2} & \frac{i}{\sqrt 2} \\ \frac{i}{\sqrt 2} & -\frac{1}{\sqrt 2} \end{pmatrix} $$ and another matrix $$ U(\theta, \phi, \lambda) = ...
2
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1answer
59 views

ArgMin and NArgMin gives different result

Im doing the same problem with ArgMin and NArgMin, however NArgMin messes up the order of the solution. Given function: ...
4
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2answers
321 views

Nonlinear boundary value problem of ODE involving principal value of integral

I have asked a question on a nonlinear eigenvalue problem (EVP). And I have worked on these for a week but I cannot solve it. I think I should first try to solve the related ODE boundary value problem ...