Questions on the analytic and numeric equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).
2
votes
1answer
36 views
Finding the root of a nested function with small values
I have reduced an error in my program to this line of code:
FindRoot[Nest[# (1 - #) k &, 1/2, 2^4] - 1/2, {k, 3.5}]
It works for $2^1, 2^2, 2^3, 2^4,$ but ...
-3
votes
0answers
53 views
Symbolic Simulations
I have nonlinear equations and I solved it for given p1 and p2 on Mathematica 7;
...
3
votes
0answers
83 views
FindRoot gives a wrong solution which obviously should not be there
I got stuck on FindRoot and I didn't see any similar problem posted, so let me explain what I am trying to do and what problem I meet here.
I try to find roots of a particular function, which in the ...
0
votes
0answers
50 views
Exposing a variable [closed]
This is the basic equation
\[Sigma][T]=E^((-20.7302 + 0.0147986 T) x) (625.646 - 3.50008 T) x^(
1.03651 - 0.000739932 T)
Then there are commands:
...
2
votes
0answers
102 views
Nest for large value of n
I am working on a problem to find the Feigenbaum constant. In this problem I have to get $f^{2^n}(1/2)$ with $f(x) = kx(1-x)$. I use Nest to get $f^{2^n}(1/2)$ but ...
2
votes
1answer
76 views
Solving a system of equations
Mathematica doesn't want to solve my exact system with 3 equations and 3 variables.
...
7
votes
0answers
129 views
Creating and using an explicit piecewise function in a convenient way
I have a set of data points that define a function in the form
curvePts = {data1,data2,...}
where
...
-4
votes
1answer
103 views
2
votes
1answer
79 views
A basic problem with Solve
I have this equation:
4b*Cos[2t]-4a*Sin[2t]==4Cos[2t]+8Sin[2t]
Which I would like to solve. Without using mathematica, you can pretty easily see that a = -2 and ...
3
votes
2answers
194 views
Mathematica does not understand (R^3)^(1/3) is the same as R [closed]
In the output from a calculation in mathematica stands a/((R^3*c)^(1/3)), with c and a ...
1
vote
0answers
65 views
Conditional statements in intial conditions?
This is potentially a daft question, but I thought I'd ask it; I have some material free to diffuse in a boundary between rn and ro; I've been able to get it working nicely for neumann type boundary ...
0
votes
0answers
61 views
Simultaneous Equation Solving Under Nonnegative and Bounding Conditions
I have nonlinear equations to solve parametrically;
...
0
votes
1answer
108 views
solution of differential equation
I have the following code that gives you a phase portrait of a 2d system and I can't understand what means the 3rd and 4th line (sol1 and sol2).
...
0
votes
1answer
46 views
Define variable relationships and dynamically update variables
I would like to define a relationship between 3 variables first and then later when I have filled two of the variables with a number, I would like to extract the value of the last value.
For example:
...
0
votes
1answer
36 views
How to delete duplicate solutions of this system of equations?
I want to find vertices (has integer coordinates) of the triangle $ABC$ with the centorid is $G(1,1)$ and orthocenter is $H(3,3)$. I tried
...
1
vote
0answers
28 views
Plot of kummer function, Hypergeometric1F1 [duplicate]
I am trying to plot the kummer function.
Where: For each a-value, there exists $\beta_1$ (the first root of the kummer function), $\beta_2$ (the second root),... of roots of the kummer function. I am ...
1
vote
1answer
101 views
Solving Intervals
In a recent question I posed, it was noted that by design, Sqrt[ blah] only returns the positive branch, even though we might want to obtain all possible symbolic solutions. So, taking care to avoid ...
4
votes
1answer
82 views
Why is FindInstance failing when I relax a set of constraints?
I'm attempting to use FindInstance to generate coordinate sets for plausible triangles with edge length distance constraints. E.g.:
...
2
votes
1answer
133 views
How to solve this equation with integers as a solution?
I want to solve the equation $$x^y + y = y^x + x$$
with $x$, $y$ are integer numbers. I tried
Solve[x^y + y == y^x + x, {x, y}, Integers]
How to solve the ...
0
votes
0answers
40 views
DSolve::overdet for system of linear PDEs
I would like to resolve symbolically the following equation:
...
4
votes
2answers
119 views
Using RSolve correctly
I am having problems persuading Mathematica to solve even the simplest recurrence relations. As an example, how would you do the following?
...
0
votes
0answers
62 views
Defining and Solving Systems of Equations Using Matrix Tables
I've defined a system of equations, but I been unable to get Mathematica to solve for the individual variables created by matrix tables.
...
1
vote
2answers
85 views
Using FindRoot with an interpolating function
This question bears resemblance to a few other questions on mathematica.SE about finding points of intersection of crossing curves. I know that the guidebook of numerics has an entry about the whole ...
5
votes
3answers
183 views
Solving a system of equations with conditions related to the number of solutions
The equation below describes a conic with oblique axis:
$$9 + 22 x + 9 x^2 + 46 y + 24 x y + 16 y^2=0$$
It is a parabola, as the coefficients in $x^2$, $y^2$, $xy$ form a perfect square. To find the ...
3
votes
1answer
70 views
Find point at which equation stops having roots (if it exists)
I am interested in the roots of this function:
f[M_, b_] := 1 - (2 M Gamma[2, 0, (1/M + b M)/Sqrt[b]])/(1/M + b M)
for fixed values of b. In particular I want ...
0
votes
0answers
49 views
Finding all roots of the system of two complex equations
I need to find all roots for the system of two complex equations. Obviously I can rewrite them as 4 real however problem remains. I have looked through routines connected with using ContourPlot ...
0
votes
1answer
56 views
Plotting query - same values on Y-axis / viewing data
I'm new to Mathematica, and have numerically solved two similar functions with the following code;
...
0
votes
1answer
81 views
Solving a system of equations using subscripted variables
I want to solve this equation:
X(i, j) + C*Y(i, j) = Z(i, j)
Where
...
0
votes
1answer
88 views
Upper bound for x
I want to ask a question about Reduce. I have a function, say f[x]. When I use the command ...
3
votes
1answer
167 views
Create Euler equation
I've tried to make some research, but without any luck.
How do I setup the Euler equation for this in Mathematica?:
$ \text{Min} \int_0^1\left(2x^2+ \left(4t-5 e^{r \, t} \right) x \, \dot{x} + ...
0
votes
1answer
57 views
0
votes
1answer
73 views
How to guess initial complex value for FindRoot
I have to solve a transcendental equation for a parameter, say $\beta$. Now, the $\beta$ has a range from $ik$ to $k$ where $i$ is the usual imaginary root $\sqrt{-1}$ and $k$ is a real number. ...
1
vote
0answers
38 views
Finding Maximum Root [duplicate]
How can I find the greatest root for a polynomial if the polynomial degree is very large.
One way is using NSolve. This command can find all roots in numeric. Then, ...
5
votes
1answer
84 views
Find the domain in which a sequence converges
I seem to have a lot of problems in the format of:
Given the sequence $a_n=\frac{n^\alpha+1}{2n^8+5}$, for $\alpha > 0$, find the values of $\alpha$ such that the sequence converges.
However, ...
0
votes
0answers
105 views
How to find the couple $a$ and $b$ of the equation? [closed]
I want to find the integers numbers $a$, $b$, $k$ of the equation
Sqrt[2 x + a] + Sqrt[b - 2 x] == k
so that the given equation has two reals solution.
I ...
0
votes
2answers
64 views
Reduce on equations involving integrals
Here's part of problem from a college physics text:
A time-dependent force F = (8.00 i - 4.00 t j) N (where t is in
seconds) is applied to a 2.00-kg object initially at rest. (a) At what
time ...
0
votes
0answers
8 views
How can I solve this system? [migrated]
Having this system:
$$\begin{cases}
2 x(x^2 + y - 11) + x + y^2 - 7 = 0,\\
x^2 + y - 11 + 2 y (x + y^2 - 7) = 0 .
\end{cases}$$
How can I solve it without using a computer?.
Thank you!
0
votes
3answers
70 views
Help solving a system [closed]
I am trying to solve this system for r and c but I get an error "Solve::ivar: r is not a valid variable.".
What is wrong here?
...
2
votes
0answers
72 views
differential equations with implicit functions
I have an ordinary differential equation that contains coefficient functions that depend implicitly on the independent variable via an algebraic equation. I am trying to go ahead and use NSolve to ...
1
vote
3answers
179 views
2
votes
1answer
72 views
InterpolatingFunction with growing Domain
I want to find roots of a function that is very slow to calculate (the function itself involves a bunch of FindMaxima) so I interpolate the function in a region where I think it likely the the root ...
2
votes
1answer
94 views
Computing the sign of the real part of eigenvalues in a 3D linearized system with 3 parameters
So I have this dynamical system given by:
$$
\left\{\begin{aligned}
x' &= a(y-\phi(x))\\
y' &= x-y+z\\
z' &= -by
\end{aligned}\right.
$$
where $\phi(x) = \mu x^3 - \nu x$ and $a,b,\mu,\nu$ ...
3
votes
2answers
131 views
2
votes
2answers
56 views
How do I generate a set of n-tuples containing integral solutions to a linear equation provided certain constraints?
Let $m,k,p$ be fixed positive integers. I want to create a table of k-tuples $(x_1,x_2,\ldots,x_k)$ comprised of solutions in positive integers to the equation below:
...
2
votes
1answer
52 views
Differentiating with respect to vectors of unspecified length
Given a function defined by
f[x_,y_] := Sum[ x[[i]] (g[y[[i]]] - g[Total[y]] - Log[x[[i]]]), {i, 1, Length[x]}]
I can easily calculate the derivative for a fixed ...
1
vote
2answers
69 views
Rearranging an equation with the sine function in it [closed]
When I evaluate Solve[a==Sin[b*c], b] to rearrange the following for $ b $:
$$ a = \sin(bc) $$
I get the following result from Mathematica:
$$\begin{align*} ...
2
votes
2answers
104 views
A While Loop with two different steps/iteration
I'd like to know if there is a possibility to solve an equation in a while loop with 2 different steps. I want the step to be small at the beginning and bigger after a certain value of sigma (sigma is ...
3
votes
2answers
76 views
Extracting Reduce results
I'm solving a Diophantine equation inside of a function using Reduce but I'm having trouble extracting the necessary parts of the answer.
For example, if my input ...
0
votes
1answer
168 views
Solving derivative of cumulative normal distribution log likelihood
I am a newbie and I'm trying to use Mathematica to obtain the symbolic Maximum Likelihood Estimation for a cumulative normal distribution. So far I have reached the step where I have the derivative of ...
2
votes
1answer
162 views
NDSolve two PDE plus one ODE, together
I have a couple of PDE (time and space/length) that are correctly managed by NDSolve, but to which I’m adding an ODE on which the acc “accumulates”, through time, a ...
