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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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104 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
68 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?
1
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1answer
54 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
32 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
78 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 ...
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1answer
102 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
82 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
61 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
328 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 ...
2
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1answer
190 views

Solving a system of PDEs on a piecewise polynomial domain

I wish to solve following system of equations with Dirchlet and Neumann boundary conditions on an piecewise polynomial (cubic spline) shaped domain as showed here. ...
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0answers
44 views

Higher order radicals (nested roots) [duplicate]

I have the following functions ...
0
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1answer
59 views

How to find all numerical roots in exponential equation? [closed]

I have this function: d = 7.61; beta = 0.0193; lnot = 74.1; morse[x_] := d*(1 - Exp[-beta*(x - lnot)])^2; and I can see there are 2 roots because when I do <...
2
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1answer
66 views

Label curves with corresponding parameter

How can Plotlegend label each curve with the corresponding value of parameter param in the code below? ...
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0answers
95 views

Simplify the equation in terms of function and coefficients?

I have two fourth order differential equations and eight boundary conditions. I want to get my result in terms of function (Y) and coefficients (let say P1, P2 and so on). I used Dsolve to get the ...
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0answers
42 views

How to convert {x -> 4} to simply 4? [duplicate]

I am using the Solve function to obtain two solutions for a quadratic, then I want to use those two solutions as input for something else but I can't because they are in the form of (x->number} ...
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1answer
42 views

Discrepancy in the solution provided by NSolve

I have a code which goes like this: First one ...
0
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2answers
64 views

Problem with FindRoot [closed]

I am very beginner to Mathematica and also a new user on Stack Exchange. I just need to find solution to the equations. I found an example similar to my problem on the internet. When I put following ...
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2answers
291 views

Solving a system of equations with constraints in specific order

This code gives about 1000 solutions for the variables a,b,c,d,e,f,g,h: ...
2
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3answers
229 views

Find the 3D region containing the origin bounded by given planes

I'm writing a code to generate the Wigner-Seitz cell of the reciprocal lattice for a given set of lattice translation vectors. For example, consider the Body Centered Cubic (BCC) lattice whose basis ...
0
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1answer
46 views

Non-decimal representation of solutions of cubic equation [closed]

I am trying to solve a cubic equation as follows Solve[2 (Sqrt[x])^3 - 1.5*x^0.5*vd == 2 (Sqrt[\[Eta]0])^3, {x}] I want to get the solution of $x$ in terms of $\...
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2answers
44 views

Cannot solve for an unknown in an equation with exponents

I have an equation I need to solve for t. I have tried the code below: ...
5
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2answers
154 views

Can ThermodynamicData be used with NSolve?

Let's say I define a function giving the enthalpy of water: ...
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2answers
47 views

Solve linear system where unknowns are functions

I have the following linear system ...
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0answers
49 views

Solve doesn't find solution after harmless modification

I have a system with 5 equations and several parameters and Mma 11.3 finds a solution after a few minutes. But if I make a harmless modification, by inserting (kfus*wtss/kfis+1) in front of the two ...
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0answers
35 views

FindRoot for a transcendental function (PolyLog)

I am trying to solve an equation involving polylog using FindRoot, I am not sure how to give the initial guess as I want to solve the equation for a variety of parameters. Here is my code: ...
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0answers
32 views

Error message in NSolve

Can anyone help me to understand what I should add here to make sure no error message is shown? the code is: ...
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2answers
60 views

Precision, accuracy and very large/small exponents with Reduce

Numerical precision/accuracy question here. I am currently working on solving nonlinear equations with Reduce. Oftentimes, ...
3
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0answers
57 views

Different output to Solve command in Mathematica changing a variable for a subscripted variable

I have a system of equations that is solved with the Solve command in Mathematica 10.2, when one of the variables is changed for a subscripted variable the answer is not the same, the difference is ...
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0answers
51 views

Solve multivariable inequlity and read the output correctly

Hi I need to solve an inequality for multiple variables, and I do not understand in a good manner the results. The inequality that I tray to obtain is $$ a+b+(2*c)+\sqrt{(-2\,c-b-a)^2-4\,(2\,c\,b+b\,...
0
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1answer
62 views

Plotting a transcendental equation [duplicate]

I would like to get this graphic: from this article. Here $\kappa$ and $\varepsilon_{dd}$ are related by: ...
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0answers
63 views

find gravity acceleration (g) using FindFit

I need some help again, with this simple exercise: Use the data to determine g, but this time use the functional form T = 2 pi Sqrt[L/g] for the period T of a ...
2
votes
2answers
75 views

Help explain failure of Solve method to solve economic equation

Below is an economic equation consisting of Y, Ki, Alpha, G, Ki, K, and two parameters Epsilon and Eta. Mathematica's Solve method computes G, in terms of the other variables, but fails to solve for ...
1
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2answers
88 views

Sum not recognized as a linear operator by Solve

When I try to solve an equation with a constant under the summation sign, Mathematica does not factor the constant out of the summation and fails to solve a simple equation. How do I make ...
1
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2answers
41 views

Why Solve works but FindRoot needs precision. How to fix?

So how do I change the machine precision so that FindRoot works? I am unsure what to put into the program to fix. I tried setting the precision and that did not seem to work for me. ...
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0answers
49 views

How to Solve a Differential Equation System Depending on Variable Solved in an Implicit Function?

I have an ordinary differential equation system need to be solved by using Mathematica. $\frac{dk(t)}{dt}=((1-\kappa(t))k(t))^{\alpha}(1-\frac{\kappa(t)}{\kappa(t)+\frac{1-\alpha}{\alpha}\frac{\eta}{\...
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0answers
98 views

Kuhn-Tucker Conditions Take Forever

I am trying to solve a Kuhn-Tucker constrained maximization problem. The variables of interest are d1,d2,dr and i. The other symbols are parameters which I have several restrictions for. It's an ...
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0answers
87 views

Trying to solve a system of equation with a subscripted variable with Reduce

When I run Reduce[expr, vars] in which one of the variables has a subscript, Mathematica gives me an output after some minutes (the system has 10 equations), but if ...
-1
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1answer
48 views

Quadratic equation with integral coefficients [closed]

Let $a,b,c $ be Natural Numbers, such that roots of the equation $ax^2+bx+c=0$ are distinct and both lie in the interval (0,1) (1,2) (2,3) (Brackets signify open interval, roots are $IN BETWEEN $ ...
2
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3answers
82 views

Checking if two expressions are related

Is it possible in mathematica to check if two expressions may be able to be written in terms of the other? The expressions I had in mind were of the form $$\alpha = \frac{1-x}{1-y}\,\,\,\,,\,\,\ \beta ...
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0answers
41 views

Why do I get a blank graph when using Manipulate with NDSolve?

I'm trying to model an SIR model using the Manipulate function so that I can change the parameters. Although, when I enter in the following code: ...
2
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1answer
45 views

Find x at a given t and f(x,t) == constant from a system of coupled PDE

Is it possible to find the speed of a moving front (produced by the below code) in which modulating beta changes the speed of the front? Basically, I am trying to map the x-values of f(x,t)=0.5 ...
0
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1answer
53 views

Implicit piece-wise function in derivative for differential equation solver

I want to set up a model/simulation that involves numerically solving a set of coupled differential equations, but at some point in time I want some of the variables to quickly jump to a constant ...
1
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0answers
80 views

Why doesn't Mathematica find solution for differential equation when Wolfram Alpha does?

I need to solve differential equation: dy/dx=tan(1/2*(Pi/2+arctan((|3tan(35*Pi/180)-x|)/(y+3)))), y(0)=0 Wolfram Alpha gives me the output in shape of plot and I need to get the formula used by ...
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0answers
39 views

Solve is taking days

...
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1answer
86 views

Why is NDSolve not working for the given system?

I'm trying to find the solution curves for a system of differential equations. In order to try to complete this task, I've attempted to use NDSolve, but I get an error that says that there are fewer ...
3
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1answer
126 views

Finding the maximum real part of roots

Suppose that I have this problem ...
1
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1answer
41 views

Missing solutions of a matrix congruence

There are some indications that the following matrix congruence might have a one-dimensional family of solutions. Also this discussion is relevant ...
3
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1answer
83 views

FindInstance and cosine system of equations

I'm intrigued by Mathematica indisposition to find an example of the following system of equations $$ \cos(x) + \cos(y) + \cos(z) = \lambda_1, $$ $$ \cos(x+u) + \...
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2answers
55 views

How to solve for variable inside of Re[ ] function?

I am trying to solve for x in the following equation NSolve[ c == Re[ Sqrt[ (((a - b I) x^2) / ((a - b I) - x^2)) ] ] , x ] It seems to be too much for NSolve.