# 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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### DEigensystem gives x-dependent eigenvalues

Bug introduced in Version 11 or earlier and persisting through 12.1. Reported to Wolfram Technical Support as CASE:4532301. I am considering the eigenvalue problem associated with the double-well ...
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### What is LyapunovSolve::meig message about?

According to Wikipedia, a Sylvester equation $AX+XB=C$ has a unique solution for $X$ exactly when there are no common eigenvalues of $A$ and $-B$. But the following code gives me a message I don't ...
44 views

### Equating both sides of the equation [closed]

I want to verify that two equations are equal. I have comparing the left and right hand side, which should print 1 or 0, but it doesn't work, it just re-prints the equations.
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### Grid for NDSolve

i want to get the output of NDsolve in the form of a tbale/grid that can be exported to .xls/.csv. NDSolve[x'[t]==Exp[t], y'[t]==cos[t], x=0, y=1,{x[t],y[t]},{t,0,10}] I am expecting an output ...
140 views

### Partial differential equation - DSolve gives no output, but solution exists

I have trouble obtaining solution for equation using DSolve: My mathematica code is given by: ...
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### Find unknown parameters from NonLinear fitted data

I obtained the fitted model from the image using the following code: ...
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### Lyapunov exponent of Delay Differential Equation

I have a Delay Differential Equation as given below ...
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### How to solve trisecting a pentagon

I thought maybe I could learn Mathematica to help me trisect a pentagon. I can't figure out how to write a Solve to get d0 on <...
36 views

### Is there a simple way to move all terms with $x$ or $y$ in the LHS and all others in the RHS of an equation?

I did the following: In the last equations, is there a simple way to move all terms with $x$ or $y$ in the LHS and all others in the RHS?
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### Looking for (possibly) two roots with FindRoot

I am looking for intersections of the a family of functions $F_n(k)$ defined over $[0,1)$ $$\frac{2K(k)n}{\frac{1+k}{\sqrt{1+k^2}}}$$ where $K$ is the complete elliptic integral of the first kind, ...
18 views

### Problem replacing an ansatz in a field equation with spin-isospin matrices

I've been lately trying to replicate a calculation but it is not working. The main problem is simple. I just have to replace an ansatz in a equation, that is (sorry for putting an image of that ) ...
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### How can I get better results using DSolve?

I am solving my fourth-order differential equation by using DSolve. When I solved it gives me an error related to precision. How can I improve my results and get better output? Any help will be ...
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### Solving trigonometric equations

I need to solve these three trigonometric equations, and figure out the a, b and c. But, this takes too long time, and I am not sure the answer is right. Thus, How can I progress my code to speed it ...
I have the following formula: $$t(a) = \frac{1}{H_0}\int_0^a \frac{da'}{\sqrt{\Omega_{r,0}a^{-2} + \Omega_{m,0}a^{-1}+\Omega_{\Lambda,0}a^2 + (1-\Omega_0)}}$$ I want to go in the opposite direction. ...