Linked Questions

2
votes
2answers
773 views

How do I get all the roots within a certain range for an equation? [duplicate]

I wish to find ALL the roots of the following equation $ x \tan(ax) - c = 0$ within a range, where a and c are constants I control. I've been using ...
1
vote
0answers
52 views

How to find x for certain y from InterpolatingFunction [duplicate]

As shown in the picture, I get the data after using NDSolve. Now I want to get the x for cetain y, how can I do this? The last three lines is the way I try to ...
70
votes
5answers
22k views

How to find all the local minima/maxima in a range

I want to find : all local maxima in range all local minima in range From those points I can interpolate and combine functions upper and lower boundary. What I am really interested in, is the mean ...
25
votes
3answers
7k views

How to find numerically all roots of a function in a given range?

It is common that I search numerically for all zeros (roots) of a function in a given range. I have written two simple minded functions that perform this task, and I know of similar functions on this ...
13
votes
6answers
722 views

Solving this challenging ODE

Consider the ODE: $$w^{(4)}(x) + (L-x)w''(x) - w'(x) = 0 $$ with some of the following boundary conditions: free: $w'' = 0$, $w'''=0$, clamped: $w = 0$, $w'=0$, pivot: $w = 0$, $w''=0$. Two such ...
9
votes
5answers
397 views

NDEigenvalues vs. FindRoot for finding the eigenvalues of Airy equation?

Say I am trying to find the first 5 eigenvalues of the differential equation $f''(x)=\lambda x f(x)$, on the interval [-1,0], with boundary conditions $f(-1)=f(0)=0$. I will try to do this 3 ways, ...
9
votes
3answers
582 views

Labeling solutions of an Eigenvalue equation involving Bessel functions

I'm solving the Schrödinger equation for a particle in an annular geometry with hard wall boundary conditions and I've reduced it to the following equation: $$J_m(k\,R_1)\,Y_m(k\,R_2) - J_m(k\,R_2)\,...
5
votes
3answers
674 views

How can I solve this equation: $(47^{(u + 1)} + 3^{(u + 1)})/(u + 1) ==50^{1.5}/1.5$?

Solve[(47^(u + 1) + 3^(u + 1))/(u + 1) ==(50^1.5)/1.5,u] The code I tried is above, but it showed me a message problem "Solve was unable to solve the system ...
5
votes
3answers
790 views

Why does the following Solve take so long?

Why does the following take Mathematica so long to reply to? Solve[BetaRegularized[0.5, k, n - k - 1] == 0.035, k] where $n = 1000$ By the way, In case there is ...
5
votes
2answers
7k views

Find all roots in range

Is there any way to check for all roots in a range? Jens' findAllRoots function is pretty good, but runs at approx. 10% of roots missed when I ran a quick check on ...
6
votes
2answers
480 views

Techniques to find all local minima of black box function with n continuous derivatives?

I have a blackbox function f on [a,b] that is known to be continuous, and has n continuous derivatives. The function uses polynomial interpolations (but isn't a polynomial interpolation itself), so no ...
2
votes
2answers
2k views

Find roots of a function involving Bessel functions

I'm trying to find the roots of a function involving Bessel functions. Here is my code ...
1
vote
3answers
615 views

Find all roots of a function with parabolic cylinder functions in a range of the variable

I want to find all roots of a function involving Parabolic Cylinder Functions. In what follows, I define 2 variables $\xi1$ and $\xi2$, which in turn depend on $\omega$. My function is then defined as ...
3
votes
2answers
198 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, $$\...
1
vote
2answers
573 views

Finding roots of a function that includes Bessel functions [duplicate]

I'm fairly new to Mathematica so forgive any stupid mistakes. Here's my function: ...
2
votes
2answers
551 views

Difficulty finding roots of an interpolation function from NDSolve

I have been trying to find the point at which one of the solutions of a system of two ODEs crosses zero. I used the method suggested in this answer to a previous question, which seemed to be the most ...
3
votes
1answer
519 views

Finding all zeroes - mysterious missing roots

Finding all the roots of a function of one real variable has been discussed extensively in e.g. Find all roots of an interpolating function (solution to a differential equation) (answer no. 2 by Jens ...
1
vote
0answers
490 views

Obtaining values from interpolating functions

A similar question has been asked in the post HERE but the current question is more complicated: I have the following differential system ...
2
votes
1answer
153 views

Complex roots of the determinant of symbolic matrix

I am trying to find multiple complex and real roots of the determinant of symbolic matrix. Someone advised me to use Muller's method. I am wondering if there is a package already written to do this ...
0
votes
0answers
146 views

Probleme with Ted Ersek's RootSearch package [duplicate]

The following question is a logical continuation of this one. The Ted Ersek's RootSearch package doesn't work with this code: ...
4
votes
1answer
113 views

Creating a For Loop for a equation that has many solutions [duplicate]

I have two equations like these. I want to create a for loop that gives to me all intersection points of the two equations. How can I do that? ...
1
vote
2answers
54 views

Finding positive region of continous function

I want to find (and plot) the positive region (within a certain domain say x<3,y<3) of a function ...
0
votes
1answer
73 views

Help me solve this equation; I believe this is a transcendental equation [duplicate]

please can someone help me solve (x*L)+B*tan(x*L)=0, solve for x when B=10;L=0.1. The equation looks innocent but I need to find 1st 5 roots of equ.