Questions tagged [equation-solving]
Questions on the analytic and numerical equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).
4,061
questions
0
votes
0answers
10 views
NIntegrate in FindRoot: s=S is not a valid limit of integration
I get an error code saying that "s=S is not a valid limit of integration" when I use the following code:
...
0
votes
0answers
30 views
Long computation time for solving two algebraic expressions
I am having two equations algebraic equations in two variables and 12 parameters
However, the Solve command is failing to provide any result even after running it for 5 hours.
How much time should I ...
2
votes
1answer
30 views
How to find the distances between two adjacent maxima in a solution from NDSolve
I try to find a general approach to plot the time evolution of horizontal distances from maximum to maximum in a solution of PDE. The solution u[x,t] normally have ...
0
votes
0answers
41 views
Need help with ParametricNDSolveValue for ODE with two variables and Do-loop
I' m trying to solve a tricky 2-nd order ODE with
ParametricNDSolveValue for boundary conditions (BCs) Y = 0 at 1.6 and ...
0
votes
2answers
45 views
how to solve the equation
I want to sole the given equation for x. Can anyone help me please to analyse the solution. Thanks
...
2
votes
3answers
98 views
Solving 5 nonlinear equations, is there a suitable way?
I'm trying to solve a set of 5 nonlinear equations using NSolve:
...
0
votes
1answer
29 views
1
vote
1answer
46 views
Need help with ContourPlot3D
I need to print out the value of x, y, and z when h==0, g==0. Help please?
...
1
vote
1answer
85 views
Solve giving solution when there is no solution
I got a strange result from Solve.
I have the following relations:
...
0
votes
0answers
34 views
Getting an analytical form $f(x,y)$ from numerical solutions of a ContourPlot
I numerically solved a set of equations which yields a solution of the form $f(x,y)=c$.
I was hoping to obtain an analytic expression for $f(x,y)=1$ (in my case $c=1$) but all I managed to do was to ...
3
votes
1answer
104 views
Solve a one dimensional heat transfer problem with NDSolve
The following problem is a 1-D heat transfer conduction problem:
where,
I am trying to solve with NDSolve like this way:
...
0
votes
1answer
44 views
How to ask Mathematica to express variables in terms of each other in an implicit function
How to ask Mathematica to give $y$ in terms of $x$ in this function? Is there a way to obtain a closed form expression for $y$ in terms of $x$?
$x=\frac{\left(y^4-1\right) \left(\coth (2 y)-\frac{1}{...
3
votes
0answers
55 views
Why does FindInstance take so long: It is faster with more restrictions than with less?
A support case with the identification [CASE:4347836] was created.
I just noted this little puzzle on twitter by Brillant.org:
\begin{align} A B C\\+ BCA\\ = CDE \end{align}
Given that $A$ is even ...
11
votes
2answers
247 views
+100
Convert symbolic to numeric code: speed up morphing
Recently I asked a question about the morphing between two functions and got two excellent answers. The accepted answer is using the continuous optimal transport theory. This seems to be very suitable ...
0
votes
0answers
29 views
I am trying to solve a system of equations but don't know how to apply a constraint [closed]
Solve[{v == 0, u == 0}, {x, y} , x > 0] is the basis of what I want. u and v are ...
0
votes
0answers
27 views
Simulating a function with no closed form solution
So I am trying to simulate a function in 3d. Suppose our function looks like this:
f=k*r*a
I am interested in simulating the numerical values of k when r is ...
1
vote
2answers
33 views
Manipulation replacements rules from Solve [closed]
Assume the call to the routine Solve[eqn==0,{x1,x2}] returns:
{{x1->a1,x2->a2},{x1->b1,x2->b2}}
I would like to ...
0
votes
2answers
78 views
Verifying that a functions attends values below something
After plotting the graph of $$f(x)=\frac{π}{3\sqrt{2 π}} (\frac{e^{\frac{-x^2}{18}}}{3} + \frac{e^{\frac{-(x - 5)^2}{2}}}{1} +\frac{e^{\frac{-(x - 15)^2}{8}}}{2}
) (1 + x^2)$$
I would like to ...
0
votes
0answers
39 views
Solving an equation: Reduce command produces failure message
I am trying to solve the following equation for c:
All variables can only take positive values and c>s. I have tried the following code:
...
2
votes
0answers
28 views
Reduce[expr,vars] behavior when vars are not present
It is officially documented that Reduce should be used like Reduce[expr,vars]. However, I've used ...
0
votes
0answers
66 views
How do I solve a cubic equation for values of x?
I have partially differentiated an equation w.r.t. x, see picture below, and want to isolate x in the equation to solve for a local maximum.
Can I use Mathematica to get it on a cubic form? and how ...
2
votes
1answer
141 views
Why FindRoot does not give all roots? [closed]
I would like to solve complicated equation and use FindRoot to find roots numerically. I do not understand the following problem. I provide the simple example. Considert the equation:
...
1
vote
1answer
49 views
Hardy Ramanujan Question [duplicate]
I revised the code I asked about earlier, but I am still not getting an output. According to Mathematica it is (mostly) correct syntax. Here is the revised function:
...
2
votes
0answers
34 views
NMinimize with real solutions, problem in the resolution and criteria for other ways to solve equations
I have multiple parts in my question. You are welcome to answer to any of them :)
Part 1 :
I have 3 equations $p(x_1,y_1)=p(x_2,y_2),\mu_x(x_1,y_1)=\mu_x(x_2,y_2),\mu_y(x_1,y_1)=\mu_y(x_2,y_2)$. I'm ...
10
votes
1answer
270 views
Numerically solving a system of many coupled non-linear ODEs efficiently?
I'm studying a fairly typical problem: a chain of $n$ coupled, non-linear oscillators. Since I want to look at open boundary conditions, the equations of motion for the position of the first and the ...
3
votes
3answers
38 views
Using Element on list of numbers when defining equations
If been looking on how to construct equations with region or domains for some variables.
Suppose I have x and that x can only be the number 1,2,4 or 7
The equation 2 x < 10 will then results in x ...
0
votes
1answer
49 views
NDSolve for Complex Algebraic-Differential Equation
Let consider the following complex equations:
$$
\frac{i x(s)}{2\pi} - \frac{\log(1+ e^{-y(s)}) - \log(1 + e^{y(s)})}{\dot x(s)}
$$
which I will cal eq1 and
$$
\...
0
votes
1answer
70 views
How this equation is solved in reals
I have tried to solve this equation $2^{-2 ^{2^{-x}}}=2$ using
FindInstance[2^(-2^(2^(-x))) == 2, x, Reals]
The result is
...
2
votes
1answer
81 views
Efficient way to list zeroes of an oscillating function
From "The First 50 Million
Prime Numbers" by Don Zagier: primes are integral roots of$$
1-\frac{\sin(\frac{\pi\Gamma(s)}s)}{\sin(\frac\pi s)}.
$$
The graph of this function looks like
I would like to ...
0
votes
0answers
44 views
Roots of complex numbers
My exercise is to find $n$ roots of a rank $n$ of a complex number. Here is my code:
...
1
vote
1answer
54 views
Is priority important in `Series` expansion?
I have a strange case here! The story begins with this equation
...
3
votes
2answers
167 views
0
votes
2answers
70 views
How I can obtain u and z?
Integrate[1/Sqrt(2*Cosh[y] - 2*Cosh[u]) , {y, z, u}] == 0.013
2*Cosh[z] - 2*Cosh[u] == 0.41
Can I obtain the parameters of u and z using above equations?
3
votes
1answer
173 views
4
votes
1answer
67 views
“Arnoldi” method for Eigenvalues inside FindRoot
I'm trying to implement a function which, given a matrix with one free parameter, would return the value of the parameter at which the lowest eigenvalue of the matrix is equal to a certain number.
...
0
votes
0answers
21 views
Problem in implementing periodic boundary condition to solve a system of PDEs with period 2 Pi/constant
I wish to solve the following system of PDEs for h1, h2 using periodic boundary conditions and specified initial conditions. When I execute Mathematica complains that the boundary conditions are not ...
0
votes
0answers
31 views
System of delay differential equations: using first interpolation as second initial condition
I am trying to solve numerically the following system of two coupled delay differential equations:
$$\dot x(t)=-\gamma x(t)-\frac{\gamma}{4}e^{i\omega_0\tau_1}y(t-\tau_1)\theta(t-\tau_1)+\frac{\...
2
votes
0answers
61 views
0
votes
0answers
45 views
Define a function including two solve solutions
I'm trying to combine the solutions coming from two NSolves and define a new function that I've to integrate.
Basically I've defined two ...
0
votes
1answer
109 views
How to solve the problem
I want to solve these equations for "r" and \theta. But, mathematica is unable to produce output. Can anyone help me please to find the values for "r" and \theta? Here, "k" can be fixed by 0.75.
<...
0
votes
0answers
29 views
14
votes
4answers
380 views
Where is the numerical solving breaking down?
I am working with a set of three coupled reaction-diffusion PDEs, and for some parameter values I am getting some not so great solutions. I have been searching documentation and tutorials, and I have ...
1
vote
0answers
49 views
NDSolveValue::fembdcc: Cross-coupling of dependent variables is not supported in this version
It seems that Mathematica can't solve differential equation when one of the arguments requires that the value of one variable is equal to the value of the other variable, when I try this I get this ...
2
votes
1answer
83 views
A question regarding 3D plot
Updated
I have an equation:
$x (z \ln z) = y$.
For different values of $x$ and $y$ we can solve this equation for z, for example, for $x = 3$ and $y =1$, we have:
...
1
vote
1answer
53 views
2
votes
1answer
42 views
Solving complex trig quations - missing solutions?
{
Sin[Pi/2 + I*Log[2 + Sqrt[3]]],
Sin[Pi/2 - I*Log[2 + Sqrt[3]]],
Sin[Pi/2 + I*Log[2 - Sqrt[3]]],
Sin[Pi/2 - I*Log[2 - Sqrt[3]]]
} // FullSimplify
...
0
votes
1answer
65 views
FindMinimum giving wrong answer [closed]
I have a very simple problem that Mathematica is giving a wrong answer to. I want to minimize the following function:
$\frac{3+t^2+6\theta +3 \theta^2}{6 t^3}$ in $\theta$ and $t$.
Now, plotting the ...
5
votes
3answers
258 views
Defining a big matrix for iterative algorithm
I need to solve this system of equations with Seidel and Jacobi methods, so I tried to define a big matrix in Wolfram.
I have read documentation, and I wrote the following command that should help me,...
1
vote
1answer
60 views
Solution of a system of ODE with Dsolve
I am trying to solve following ODE with Dsolve.
a1[t_] = 2 - 3*Exp[-2*t];
a2[t_] = 1 + Exp[-3*t];
a3[t_] = 4 + Exp[-5*t]
$B=\begin{bmatrix}a1[t] & a2[t] &...
0
votes
1answer
61 views
How to substitute by NDSolve solution to plot a new function
Assume I got some function by NDSolve , like y(t)
...
