# 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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### Poincare section keeps running without giving results

I am trying to find the Poincare section as given in Figure 7 of this paper. This is the code that I am using for it: ...
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### Integer points on a line segment

I have two rational points. They are denoted below in black and they define a line segment. Find integer points on this segment. ...
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### I have a error on my code but I can't find it!

I have a problem by my code I can't find it yet!! ...
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### How to check equivalence when variables in equations are replaced by their negatives?

In a previous post about checking whether two systems of equations are equivalent, the suggestion was to use the Reduced Row Echelon Form, which was great. However, I now want to consider an ...
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### Simplifying an ODE in Bessel notation

I have the following Mathematica code: eq[r_] = 3 (1 + 2 a) g1 r y[r] - 2 (2 y'[r] + r y''[r]); DSolveValue[eq[r] == 0, y[r], r] This gives me the ...
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### Plotting a set of equations [closed]

I have two following eqs: $S = a M^2 + \beta + \alpha Log[a M^2]$ $t =\lambda^5 M^5 (3 + \lambda^2 M^2)/ 3\delta (1+\lambda^2 M^2)^2$ where a, $\alpha$, $\beta$, $\delta$ and are constant parameters. ...
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### FullSimplify returns complex number even though assumptions make it real

EDIT: Maybe the scope of my question is really how to solve in closed-form for the real roots of the cubic, conditional on being in the parameter space where the discriminant is positive. So I'm ...
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### How to check if two homogeneous systems of linear equations are equivalent?

How can I check if two homogeneous systems of linear equations are equivalent in Mathematica? Given two systems of equations: System 1: \begin{cases} 2x - 3y + 4z = 0 \\ -5x + 6y - 7z = 0 \end{cases} ...
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### Equation solving and variable manipulating issue

Another difficulty I am facing in Mathematica. I have an equation with r and P as variable. when I put value of P and then solve for r, I am getting a solution. but if I try to solve for r first and ...
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### Plot an expression in which a variable satisfies an equation

My question is very simple. I have a function $f(r)$ with some other parameters and I want to plot ${f'(r)}/{4\pi}$ vs P where r is satisfying the equation $f(r)=0$. I don't know where am I doing ...
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### Estimation of particle displacement in meters from consecutive images

I have two images (img1,img2) in which the particles have moved. I obtained their displacements from the ImageDisplacements command, but I don't know how to ...
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### FindRoot[NDSolve...] [duplicate]

I have a function OdvodNaPolu: $\mathbb{R}\to\mathbb{R}$, and I want to find its zero. The function contains NDSolve and based ...
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### Reliability of DSolve to ensure existence of analytic solutions

So I've been wondering about this for a long time. Of course, Mathematica DSolve can be a monster slayer sometimes but as Mathematica as it can get, the output results usually tend to be not ...
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### "SixJsymbol" function unable to be simplified with long run times due to not real components despite including the assumptions

I'm trying to perform some quantum mechanical calculations using Wigner-Eckhart theorem by running them through Mathematica. However, despite including the assumptions the calculation is unable to be ...
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### How to collect the terms with $m_1$ in common, $m_2$ in common and $m_3$ in common in a large expression?

How do I separate the terms in the following expression having $m_1$, $m_2$ and $m_3$? Please help me out. I shall be really grateful. ...
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### Assign condition to variable

I would like to integrate the output of a Solve. But Solve gives me an expression with some conditions. I would like to assign this condition to variables. For example: ...
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### How to solve the partial differential equations?

equation is and the symbol solution is $u[x,y]=e^x \sin(\pi y)$ mathematica code ...
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1 vote
The question is: If the tangent line to the curve $y=e^x+x$ at point $(0,1)$ is also a tangent line to the curve $y=\ln(x+1)+a$, then $a=$ _______ My method is like this, very cumbersome! ...