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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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: ...
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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 ...
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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 ...
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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 ...
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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 ...
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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: ...
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1answer
29 views

FindRoot: equation with integral on parametric domain

Writing: ...
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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? ...
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1answer
85 views

Solve giving solution when there is no solution

I got a strange result from Solve. I have the following relations: ...
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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
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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: ...
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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}{...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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: ...
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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 ...
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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
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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: ...
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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
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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
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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
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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 ...
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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 $$ \...
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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
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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 ...
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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: ...
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1answer
54 views

Is priority important in `Series` expansion?

I have a strange case here! The story begins with this equation ...
3
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2answers
167 views

Strange NSolve failure [duplicate]

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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
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1answer
173 views

Solving PDE and avoiding singularity

I have the following question about solving a PDE: ...
4
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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. ...
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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 ...
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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
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0answers
61 views

Finding solutions of a complicated equation

Consider the following setup ...
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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 ...
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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. <...
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0answers
29 views

How to fully simplify the reduce

Consider the following Reduce statement ...
14
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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
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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
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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: ...
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1answer
53 views

Bug in FindRoot?

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2
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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
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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
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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
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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] &...
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1answer
61 views

How to substitute by NDSolve solution to plot a new function

Assume I got some function by NDSolve , like y(t) ...