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

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58 views

Solve equation of motion with Dirac-fermions?

I want solve a System with n equation of Motion in first order. In this equation of motion are creation and annihilation operators of Dirac-fermions. I cannot figure out how to describe the creation ...
1
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0answers
51 views

Analytical solve for biharmonic equation

I want to analytical Solve or numerical solve by Mathematica a biharmonic equation with homogeneous boundary conditions homogeneous? I considered its solution using Fourier analysis, which is not ...
6
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1answer
111 views

FindInstance fails to find integer solutions to glaringly obvious problems

This is a continuation question to Sums as rational vector dot products with a basis constants vector. Consider the following FindInstance query. Looks easy, doesn'...
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0answers
47 views

How does Mathematica solve a system of degree two polynomial equations? [on hold]

How does Mathematica solve a system of degree two polynomial equations? I am running code that yields {} (no solutions), but I would like to replicate the manipulations by-hand. Another concern: my ...
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0answers
48 views

Iterating over pairs in a list

Take a look at this code: ...
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2answers
50 views

Plotting many solutions of FindRoot

To an earlier problem, @Rhermans provided the following solution: ...
4
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0answers
38 views

A simple expression on which `Reduce` fails

The conditions in x ∉ Integers && y ∈ Integers && y == -(1/2) + x/2 are inconsistent but Reduce does not solve ...
4
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2answers
54 views

Combinations of variables that satisfy my inequality

This question is a continuation to one answered by kglr here. In the following situation, I find that given my assumptions, it is indeed possible for $g$ to be negative. ...
4
votes
3answers
137 views

Using Assuming with Reduce

I have the following code that includes Assuming to cut through irrelevant detail, or so I had hoped. ...
4
votes
1answer
47 views

Solve/Reduce not working on a function with a condition/domain restriction?

I'm working with a trigonometric function, so I thought it would be convenient to set a condition to restrict the domain so I wouldn't have to specify it in the solve function each time. Here is a ...
3
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1answer
83 views

Mathematica has trouble solving this coupled differential equation

I'm trying to solve the coupled differential equations: ...
1
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0answers
94 views

Solve differential equation

I want to solve the next differential equation, fun = t^2*x''[t] + 4/3*t*x'[t] - 2/3*(1 - (L^2)/(6*t^(2/3))) x[t] - (2*L^2)/(45*t^(2/3)) == 0 DSolve[fun, x, t] ...
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0answers
73 views

using power series to numerically solve NS equations of a compressible viscous flow in cylindrical form [on hold]

Following this and this questions, I am trying to solve Navier–Stokes continuum equations in cylindrical form for a axisymmetric, compressible and vicious flow using power series. Consider the ...
1
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2answers
76 views

Problem with Solve (Lagrange multiplier)

I'm trying to solve a simple maximization problem, which I can easily solve by hand using the Lagrangian method. I want to maximize UH subject to ...
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0answers
35 views

How to solve the following nonlinear differential equation? Numerical [closed]

where f(vt)=sin(v t); T_{1} (0)=1;T_{2}(0)=0;\Phi(m,k)=constant
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1answer
33 views

Trying to obtain the 2D version of a graph 3D graph

I'm trying to plot this function: f[x_, c_] := 527.5658823401758`*(1 - Erf[(2 x - 1)/(2^1.5)]) + 400.6284776272996`*(Erf[(2 (-c) + 1)/(2^1.5)] + 1) I ...
0
votes
1answer
32 views

Problems with symbolic expression from Solve[]

I have an equation which is solved by Solve[]. When I define the variables with real numbers, I get an exact solution. However, when I'm trying to use the symbolic expression for the solution, I ...
0
votes
1answer
31 views

Use Solve for two Functions to find 1 common Variable

I have 2 functions that look like this: F[t_,d_]:= 10+t+2d G[t_,d_]:= 5+t+d I'd like to solve this in such a way to know for which t both Function have the Same value. I assume that this won't be ...
-1
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2answers
129 views

Why the NullSpace can not find solution when the Det[t]==0

This question contained the problem of NullSpace, but previous ones not. This is a problem seems like my previous one, but there is some details different. I find that perhaps one method can not ...
2
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1answer
67 views

Convert trigonometric expression into other forms using just a specific set of identities

I am trying to convert a trigonometric expression like sinθ/(1 - cosθ) into cosecθ + cotθ or ...
4
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1answer
117 views

Equalities using FullSimplify?

How can I know if $(-2 + a (1 + i))/(a - 1), a=(-2 i (z - 1))/((z - i) (1 + i))$ is equal to $(1+i)(1-z)$? I tried FullSimplify$[(-2 + a (1 + i))/(a - 1)]$ and I got $-(2 (1 + i) (i (-2 + z) + z))/(i ...
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0answers
41 views

There is no non-trival solution when Det[t]==0 (t is a complex matrix) [duplicate]

This is a different question with pevious one although they seems like the same. In that question m=1, the matrix t is not a complex matrix, when I change Kh as Kh=Rationalize[0.211,0], the problem is ...
1
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0answers
76 views

“Simplify” or “Evaluate” an expression until it is expreseed in terms of some other variables

Let's say we have the following relation between different variables: ...
-3
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0answers
79 views

There is no non-trival solution when Det[t]==0

The previous question is irrelevant to the solution of tx==0, and thus is obviously different with the present one. t is a generated matrix with a parameter kz. Through solving Det[t]==0, the ...
1
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2answers
143 views

The solutions of Det[t]==0 do not satisfy the equation

t is a generated matrix with a parameter kz. Through solving Det[t]==0, the solutions, i.e. kz, are obtained. When I substitute any one solution in Det[t], the result is a large number, why? How to ...
0
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1answer
15 views

Evaluate an expression in terms other variables when lots of equations are involved

Unless I misunderstood something, this is different from a similarly worded question because I am not asking for the relationship between different variables here. I want to convert an expression ...
0
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2answers
53 views

Express variable in terms other variables when lots of equations are involved

Consider the following equations: W*BP == X*PC Y*AQ == Z*BQ AC^2 == AB^2 + BC^2 PQ^2 == BP^2 + BQ^2 AP^2 == AB^2 + BP^2 BC == BP + PC AB == AQ + BQ Let's say, I ...
3
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1answer
77 views

Guess Diophantine equation from its solutions

Take for example the equation $$ n^2=x^2+y^2+1 $$ where $x,y$ are integers. This equation admits solutions only for some values of $n$, to wit, $$ n=1,3,9,17,19,33,35,51,73,81,99,\dots $$ Can we ...
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0answers
106 views

The Euler-Lagrange first integral [migrated]

How to calculate $\frac{d\phi}{dz}$ from following equation: $$A\frac{d^2\phi}{dz^2}+\cos(\phi)\sin(\phi)=0,$$ where $A$ is a constant?
4
votes
2answers
183 views

LinearSolve on a singular matrix

I have some singular transition rate matrices $m$ (columns add to zero). They have exactly one zero eigenvalue that I want to find the corresponding eigenvector of (the rest of the eigenvalues are ...
4
votes
3answers
146 views

How to make vector field plot from NDSolveValue Solution?

I am solving Laplace equation on circular domain from which i get solution for potential. The code I used: ...
1
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2answers
64 views
1
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1answer
47 views

Increasing accuracy of solving overdetermined linear system

I am given $48 \times 48$ matrix $A$ and a vector $b$ and I would like to solve system $Ax = b$. I know that $A$ is underdetermined, i.e. there exist many solutions for $x$. Due to some considerations,...
1
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0answers
47 views

Solve polynomial system

I am trying to solve ...
3
votes
2answers
206 views

Solve system of equations

I wrote the following code: Solve[{x == VIN/VOUT, VOUT == 5 VIN}, {x}] Mathematica does not solve it. How can I get the result x=1/5? Thank you so much for your ...
0
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1answer
33 views

Minimax Optimization Over and Interesting Function

n=2; (i_1,i_2)= i mod 2 for example (0,1)=1 mod 2 or (1,1)=3 mod 2 $$f_i(s_0,s_1)={s_0}^{i_1}{s_1}^{i_2}{(1-s_0)}^{1-i_1}{(1-s_1)}^{1-i_2}$$ $$r(s_0,s_1,x_1,k_1)=...
2
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0answers
83 views

How to Solve this Fokker-Planck Equation?

I need to solve this Fokker-Planck equation in Mathematica and my attempt to perform this integration is above: My first attempt is above: ...
1
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1answer
52 views

How can I solve this inequality?

How can I find the answer to this inequality for Lambda? ...
0
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0answers
101 views

Approximate the relationship between 6 nonlinear functions involving elliptic integrals

I am trying to solve a physics-related problem, which results in approximating a relationship between 6 symbolic functions $F_1(\alpha,\beta ,x_0,y_0),F_2(\alpha,\beta ,x_0,y_0),...,F_6(\alpha,\beta ,...
2
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3answers
236 views

How can I remove the FindRoot error from my calculations?

If you run my calculations given below ...
0
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1answer
80 views

Get Polynominal Coefficient of non linear equation [closed]

I have a non linear equation and want to create a polynomial of that. For this I have to calculate the coefficients. The problem is that the equation is a little bit long. So I wanted to do it with ...
3
votes
3answers
157 views

InverseFunction fails to invert $e^{-x/2}-e^{x/2}$

I need to invert a function. I want to isolate the x basically. By the looks of the graphic I plotted, the function seems to be invertible, however when I call <...
0
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0answers
35 views

PolynomialGCD::lrgexp: Exponent is out of bounds for function PolynomialGCD.Error

Not exactly sure whats wrong with my code but it keeps giving me a PolynomialGCD: Exponent is out of bounds for function PolynomialGCD error. The equation that I do NSolve for is very big and it takes ...
1
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2answers
95 views

Solving Complicated Equation Using Mathematica

I have to solve the following equation using Mathematica. $\frac{8 \pi \sqrt{a^2+b^2}\ e^{-a \pi^2}}{b}(b\ \cos b\ \pi^2+a\ \sin b \ \pi^2)\int\limits_0^1 e^{-a\ \pi^2 u^2}\cos b\ \pi^2 u^2 ~du=1$. ...
4
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2answers
54 views

Finding inflection points of 2D BSplineFunction

This code creates a jagged line in two dimensions and fits a BSpline function to it. ...
0
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2answers
43 views

Using Assuming for conditional expression in Solve

When I solve the following equation I obtain a solution with a conditional expression Solve[{0 == k Sin[x - y] - Sin[x], 0 == k Sin[y - x] - Sin[y]}, {x,y}] How ...
0
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1answer
26 views

How can I use NSolve on my equation for an interval?

I have two equations given by ...
0
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0answers
64 views

How to involve more cpu cores?

I'm working on Mathematica 11 (Lenovo Laptop, Core i7 cpu, 16GB Ram, SSD storage, windows 10 pro), part of my work is definite double integral, the evaluation time of this integral takes between 50 to ...