Questions on the analytic and numeric equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).

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1
vote
3answers
147 views

Find all solutions which satisfy the given conditions

Let $$ m=9n^3+30n^2-9n $$ where $n \in \mathbb{Q^{+}}$ and $m \in \mathbb{Z} $ . Find all solutions which satisfy the given conditions. So I've tried to solve this manually and I was able ...
1
vote
1answer
105 views

Wrong root when using numerical values

I have the following inequality: $$ \sqrt{\frac{a}{2x}}+ \frac{b}{1-\frac{a}{a+\sqrt{a(2bx + a)}}} + \frac{a}{2x\frac{a}{a+\sqrt{a(2bx + a)}}\left(1-\frac{a}{a+\sqrt{a(2bx + a)}}\right)} < f $$ on ...
2
votes
3answers
453 views

Solving an equation involving an integral

How do I get the following into Mathematica, solving for $a$: $$ 0.7 = 1 - \frac{2}{a} \times \left[ \frac{1}{a} \int_0^a \frac{x}{\exp(x)-1}\mathrm dx + \frac{a}{6} - 1\right] $$
1
vote
1answer
73 views

Improving strategy to solve this constrained root-finding problem

I am looking for roots of the function eqs defined below. It has $2k$ unknowns and returns a vector of $2k-1$ components. The sole purpose of the following block ...
0
votes
0answers
29 views

Solve involving simple cancellation on both sides fails when there are too many constants

I've been working with a number of equations of the form x = A * B * x ^ C where I need to solve for x--basically, equations ...
0
votes
1answer
192 views

Nonrectangular tensor encountered [closed]

I am trying to solve a system of equations which characteristic matrix: ...
0
votes
0answers
40 views

Probleme with Ted Ersek's RootSearch package [duplicate]

The following question is a logical continuation of this one. The Ted Ersek's RootSearch package doesn't work with this code: ...
0
votes
3answers
131 views

Manipulation linear systems of equations

I have the following system of equations: i1 = ix - β*ib; i2 = (β + 1)*ib; i3 = ix + ib; vx = i1*Rc + i3*Rb; v1 = i2*Rϵ + i3*Rb; v1 = -ib*rπ; I tried using: <...
2
votes
0answers
99 views

Solving this system of nonlinear equations

Edit Interestingly, I realized solving my problem with $2n$ equations appeared to be more efficient than using mathematical results on the solutions to reduce the problem to $n$ equations (the $n$ ...
1
vote
1answer
95 views

Help with findroot optimization

I'm trying to solve the set of coupled equations $$\frac{-N -2( \lambda + N(\frac{\beta}{\epsilon}-\lambda))\upsilon_l + N \upsilon_l^2-2(N-1)\gamma\upsilon_l^3}{\gamma-2\lambda\upsilon_l^2+\gamma\...
3
votes
2answers
133 views

Show Factorial instead of Gamma in the result of RSolve

Now I wanted to solve for a recurring function with RSolve. Here's how I tried: ...
4
votes
0answers
149 views

Complex boundary conditions and NDEigensystem

I am having difficulties implementing a Neumann value when numerically solving the Navier equation using NDEigensystem. The Navier equation is given by $\nabla^2 \vec u + (p^2 - 1) \nabla(\nabla\...
0
votes
1answer
79 views

Invert and fit implicitly defined curve

I need to fit an implicitly defined curve. I thought I could get some data out of Solve, and then using FindFit. Therefore, I ...
-2
votes
1answer
63 views

How to solve this non-linear equation? [closed]

b=12 a=2.787 solve[b/x-((1-(a*(((b x)/(b+2 x))^(4/3))))^(-2/3))- ((1+(a*(((b x)/(b+2 x))^(4/3))))^(-2/3))==0,x] I gave the above code and the output came ...
1
vote
1answer
57 views

Mathematica cannot find intersection of two functions [closed]

Why mathematica cannot solve this extremely easy equation? [![My functions][1]][1] g[x_] := -x + 2 h[x_] := 3 x f[x_] := -x^2 + 4 http: // i.stack.imgur.com/...
2
votes
1answer
150 views

How to put the result of NDSolve in a function?

I have solved an ODE with NDSolve, and put the result in S: S = NDSolve[{y'[x]==(y[x]^4+y[x]+1)^(1/2),y[0]==0}, y, {x, 0, 100}] But i don't want to plot y[x] ...
4
votes
1answer
117 views

How do I solve a system of equations for only one variable quickly?

I have four order-2 polynomial equations in four unknowns. Call the unknowns x1,x2,x3,...
0
votes
3answers
107 views

Solving cubic equation with unknown coefficients

I am trying to solve a cubic equation with unknown coefficients (p and t), here is the code: ...
1
vote
2answers
88 views

Solving an equation of one parameter over a range of values of that parameter [closed]

How can I use NSolve the following situation (to rectify a cycloid arc mapping with hashes etc.)? For a specific value on the right-hand side, I use ...
1
vote
4answers
161 views

Find zeros of a transcendental function

Mathematica 10 can not give me solution of this equation ...
0
votes
1answer
76 views

How to solve a linear system inside Manipulate and use the result for Plot?

I typed a code for showing a plane and a line, and solve a system, but I can´t show the intersection, because I don´t know. Here is a minimal working example for understanding my problem ( the real ...
0
votes
1answer
75 views

Implementing AiryAiPrimeZero function

There are some functions implemented in the Wolfram Language related to Airy functions. For example, AiryAi, AiryAiZero or ...
1
vote
3answers
168 views

Find zeros of function in 2 variables

I have two functions $f(r,\phi)$, and $g(r,\phi)$. What is the best way to find the curve in the plane $(x,y)$ or $(r,\phi)$, over which $f(r,\phi)=g(r,\phi)$? I know how to plot it, using ...
4
votes
3answers
99 views

How can I stop Solve returning the value of a root encapsulated in a list?

I have a Solve similar to the following: ...
2
votes
0answers
50 views

Why doesn't RSolve work here? [closed]

RSolve[ {θ[n + 1] == θ[n] + 0.25*ϕ[n], ϕ[n + 1] == ϕ[n] - 2.5*Sin[θ[n]], θ[0] == π/2, ϕ[0] == 0}, {θ[n], ϕ[n]}, n] What's wrong with my code? I know ...
1
vote
1answer
73 views

FindRoot::Istol error

I recently tried to find a root with FindRoot in Mathematica. I know that the problem has a solution, but when using FindRoot, this error appears : FindRoot::...
1
vote
0answers
67 views

Why FindRoot fail in this case?

I'm trying to solve a set of equations: $$\frac{\epsilon+(k(1-N)+2\beta)\upsilon_l-\epsilon \upsilon_l^2-2\Omega(1-N)\upsilon_l^3}{-\Omega\upsilon_l^4+k\upsilon_l^2-\Omega}=\sum_{j\neq l}^N\frac{2}{\...
1
vote
1answer
59 views

Assigning solutions to a variable [duplicate]

If I do Solve[x+1==0, x] then I get {{x -> -1}} But I want to assign the solution -1 directly before seeing the result, ...
0
votes
0answers
59 views

FindRoot for vectors

My problem is the following: quad = 26; R is a quad x 3 matrix, lpand ...
0
votes
1answer
126 views

Conditions for real roots of a cubic polynomial with complicated, yet constant, parameter values

Can anyone find conditions on the following parameters $\sigma_{\ell}$, $\mu_{\ell}$, $d_{\ell}$ and $\sigma_M$ such that the cubic: $$ (d_{\ell}-d_{\ell}\sigma_M)\ell^3 + (2d_{\ell}+\mu_{\ell}-\...
1
vote
0answers
85 views

Solve works with numbers, but not with free variables [closed]

The following code prints the correct solution for variable a (2.23). But if I comment out the five assignments given at the top, the code fails. When I remove ...
1
vote
1answer
71 views

Solving a differential equation with a specified “input vector”

I have the following differential equation: ...
1
vote
0answers
80 views

Solving a tensor equation in xTensor [closed]

I want to solve the following equation $\frac{1}{4} R_{ab} g_{cd} - \frac{1}{2} g_{ab} R_{cd} + 4 R_{ab} g^{ef} \nabla_e \nabla_f R_{cd} + 2 g_{ab} R_{cd} g^{ih} g^{ef} \nabla_e \nabla_f R_{ih} = g^...
5
votes
5answers
170 views

Non-algebraic equation in the set of complex numbers

The following equation in $\mathbb{C}$: $4z^2+8|z|^2-3=0$ is not algebraic and has 4 solutions : $\pm\frac{1}{2}$ and $\pm i\frac{\sqrt{3}}{2}$. The Solve function in Mathematica only returns the 2 ...
2
votes
0answers
99 views

Solving a non-linear equation in Mathematica with many variables

I have a beautiful equation, where I am trying to compute for R2. I am using Mathematica. So far every single time that I have tried to use Solve[] or Reduce [] the computation takes forever. I hope ...
2
votes
1answer
36 views

Specifiying values in a system of equations

Suppose I have system of equations, for example Clear[a, b, c] Reduce[{RCI7[{a, b, c}] > 0, RCI7[{b, c, a}] > 0, RCI7[{c, a, b}] > 0}, {a, b, c}] // N ...
0
votes
2answers
55 views

Please, can someone solve this equation [closed]

Solve the equation: e^(at)+e^(a(t-T)) = 2. Please can someone help me to solve this equation. I need a in terms of t, T.
0
votes
1answer
72 views

a question about Nminimize [closed]

I have 10 equations and 10 unknown parameters such as alpha1,alpha2,a1,a3,... which I want to find them by minimizing ...
5
votes
0answers
97 views

Find regions in which the roots of a third degree polynomial are real

I have to find the roots of a third degree polynomial in $\phi$ that depends from 3 parameters, namely $t,s,w\in \mathbb R$. In order to do that I've used the command ...
4
votes
2answers
127 views

Torus-geometry algebraic equations using Nsolve and Reduce

Somehow a set of naive-looking equations cannot be solved by using NSolve. Mathematica returns a message like this: ...
-1
votes
1answer
40 views

Finding the set of solutions of an equation [closed]

I have a very simple problem. I have an equation f[x] == 0, where f[x_] := x^2-4. In output, I want to get the set of ...
1
vote
1answer
41 views

defining output Solve

I'm just starting with Mathematica and I was having a small question: How can you "define" the outcome of a "Solve" in Mathematica? Here is an example from mathematica: ...
5
votes
0answers
115 views

How to find an algebraic representation

I want to find matrix representation of some algebra (Clifford algebra Cl(3,1) in this case). Here is an example, which I would like to get and then extend to higher dimensional matrices. Suppose we ...
7
votes
2answers
338 views

How can I find solutions for this equation?

I have a function cxyz[s1, e1, s2, e2], and I want to find at least one set of {s1, e1, s2, e2} for which the function's output ...
1
vote
1answer
58 views

Problems with solutions obtained from Reduce

I am solving a problem using Reduce, and having a difficulty with understanding the answers I obtained. I was solving ...
1
vote
0answers
64 views

Getting Solve::nsmet error message

I have the following equation: Profit[Fc_] = p (T - Fs - Fc)^(rho*phi) * Fc^phi * Mc^psi - w*Fc and I tried ...
2
votes
1answer
103 views

Reduce not solving linear equation

I have a long equation in 7 variables but the equation is linear (affine) in x. But when I try to solve with Reduce, it keeps running forever. With Solve, I am able to get an answer. Usually I have ...
0
votes
0answers
20 views

Numerical resolution of equation with trigonometric expressions [duplicate]

I have difficulties to solve this equation : NSolve[(x^3 + Sin[x]*Cos[x]) == 0, x] I receive the following error message : This system cannot be solved with ...
5
votes
2answers
201 views

Series solution of the Lane-Emden equation

I have the following problem: I'd like to show how the Lane-Emden equation would look like if someone would solve it as a series. Here's the code: ...
0
votes
1answer
303 views

How could I solve this Reaction-Diffusion PDE using mathematica?

I'm modeling a problem with PDEs, So I gotta solve numerically this Reaction-Diffusion Partial Differential Equation $$ \frac{\partial u(t,x,y)}{\partial t}=D\Big( \frac{\partial^{2}u(t,x,y) }{\...