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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1answer
68 views

problem in solving a non linear differential equation

I'm trying to reslove a differential equation with one of the coefficents depending on the dependent variable, it's a simple dynamic system, with one of the coefficients that can assume 2 values: The ...
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1answer
48 views

How to solve three simultaneous equations on Mathematica to get N in terms of X,Y and Z?

I am trying to solve a system with 3 equations 3 unknowns. My code is following X = A1*S + N1 Y = A2*S + N1 Z = N1^2 + A1N1S + A2N1S + 2A1A2*S^2
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1answer
99 views

How can I get intersection points of two adjustable curves dynamically?

I need to show the intersection points of any two lines and dynamically adjust the lines to get new intersection points, what is the easiest way? ...
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2answers
308 views

Behavior of Solve with $Assumptions changed in 12.2

Something changed with Solve between versions 12.1 and 12.2. 12.1: ...
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0answers
21 views

Problem with nested FindRoot definition [duplicate]

I'm using a thermistor to measure temperature, and have defined a function using datasheet function which gives temperature as a function of measured resistance. ...
0
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1answer
126 views

How to solve following equation with multiple random variables

How can I program the following problem into Mathematica? $X,Y$ are i.i.d. Exponentially distributed random variables. Such that $X\sim\exp(1), \ Y\sim\exp(1)$. All other variables are positive real-...
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1answer
42 views

Collinearity of a given points with a parametric equations

I have points moving on a circular orbit with parametric equations I want to find "t" when they lie on a single straight line (Collinearity) ...
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1answer
44 views

Why does `Solve` repeat the same solution twice?

I have the system of matrix equations {s.n == n.s, n.n == 0, s + n == f} where ...
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3answers
36 views

System of equations and distinct result sets

Question on the below system of equations: First off, in section 1 below, I had to manually play with that 4th parameter (300) so I can finally see that there are actually 96 sets of solutions. Is ...
5
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2answers
192 views

Solving trigonometric equations with two variables in fixed range?

I am trying to use 'Solve' function to solve two trigonometric equations with two variables a1 and a2 (with range ...
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3answers
67 views

How to make sure that the root of the given equation is a multiple of $\pi$?

I am using FindRoot to find the roots of this two-variable equation ...
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0answers
43 views

Input Value lies outside of the range

The following control problem is formulated using Lagrangian equation. I spent a lot of time to get rid of the "warning: input value lies outside the range..." and this is my last resort and ...
4
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3answers
187 views

Is there a way to print simple roots as Root objects?

I like the typesetting of Root objects. For example: 3-Sqrt[2]+Sqrt[3]//RootReduce But can I get the same root object with its typesetting for simple roots like ...
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0answers
42 views

Use Euler's Method to solve y' = 1+ x/Sqrt[y], y(1)= 9, h = 0.01 [duplicate]

[Laplacian]t = o .01 F[{x, y}] := {y' == 1 + x Sqrt[y], y[1] == 9}; It did not work and I do not wnow what else should I add
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1answer
57 views

Solution of a system of three equations, one equation involving the real part of an integral

Let $a,b,c$ and $t$ be complex numbers. How can one solve the following three equations for $a,b,$ and $c$ in terms of $t$: $$ a^2 + b^2 + c^2 + 2 t =0, $$ $$ a^4 + b^4 + c^4 - 2 a^2 b^2 - 2 a^2 c^2 -...
2
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1answer
109 views

PDE system. convection dominated, method AffineCovariantNewton failed, etc

I'm trying to solve numerically the following system in a rectangular region, $\begin{align} \cos\theta\frac{\partial\beta}{\partial x}+\sin\theta\frac{\partial\beta}{\partial y}&=\beta s\\-\sin\...
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0answers
57 views

Nonlinear Differential Equation with Paramaters in Sqrt Function

For a university project, I am trying to see if my system will have choked flow and also plot the resulting pressure spike. I set up the system below to try to model the transient response. I am able ...
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0answers
14 views

Extract expressions for desired variables from system

I have a large system S of polynomial equations, involving twenty variables from a set A and another seven variables from a set B. There are 146 equations. I want expressions for the variables in B, ...
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1answer
63 views

Error message when solving simultaneous differential equations

I am trying to solve the following set of differential equations to obtain $\phi[t]$, $y[t]$, and $z[t]$. The 3 differential equations are here: ...
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0answers
39 views

Speed of Nsolve

I'm trying to solve a set of equations. There is about 1000 variables and 1000 polynomials. Since this is a polynomial and the number of variables and equations are the same, it is solvable. But I'm ...
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11answers
3k views

Plotting the Star of Bethlehem

Christmas is around the corner! In preparation, consider the polynomial f[x_,y_]:= 1/10 (4 - x^2 - 2 y^2)^2 + 1/2 (x^2 + y^2) and define $r=(f_x,f_y)$ using the ...
2
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2answers
59 views

Solve for two variables but output second variable in terms of first variable

Here are some equations for illustration: Format[Solve[{4*r1^3 == r2^2*(3*h), t*r2^2*(h - d) == r2^2*(h + d)}, #] & /@ {{h, d}}, InputForm] Here is their ...
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1answer
51 views

How to find an equation of a line using Mathematica [duplicate]

(b) Find an equation of the secant line through $ (−2, f(−2)) $ and $ (−1, f(−1)) $. Define this line as $ fs1(x) $ in Mathematica.
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2answers
97 views

Solve an interpolating function [duplicate]

I have been working with interpolating functions recently and have two functions as a result of an interpolation of two co-ordinate lists. The code I used: ...
4
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0answers
67 views

How to get an asymptotic of the real-valued branch of the inverse function?

Consider function $f:\mathbb R^+\to\mathbb R^+$, defined as $f(x) = x + x^2\left(1 + \log x\right)$. I need to find an asymptotic approximation of its inverse function $f^{\small(-1)}\!:\mathbb R^+\to\...
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0answers
30 views

Importing equations generated in subpackage to be solved in another subpackage

I have a package which contains two subpackages: one ("`MOTSimulator`MOTGenerator") which generates a systems of differential equations of the form ...
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1answer
56 views

FindRoot[] with dependent interval [closed]

I would like to use FindRoot for a problem of this type: {f[x, y] == 0, g[x, y] == 0, 0 < y < x < 10} My problem is ...
1
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1answer
94 views

Solving a system of PDE-ODE with Dirichlet condition

I'm trying to solve a system of one PDE and one ODE that are dependent on time and distance (H[x,t] and P[x,t]) with the distance varying between x = 0 and x = xmax. The value for function P is 0 at x ...
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0answers
46 views

Unexpected behaviour of SolveAlways

My problem is quite simple and I cannot spot if this is my mistake or some malfunction of mathematica. I am using ...
1
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1answer
57 views

How to obtain algebraic solution of a logarithmic equation. (mathematica)

How to obtain algebraic solution of the logarithmic equation expression=-b n + Exp[t] lambda n Solve[ expression == 0, t] The output should be $$t=Ln \left(\frac{b}...
2
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2answers
69 views

Reduce inequality does not finish

I am trying to show general cases of symmetry of regions. However, for the following, Reduce does not finish: ...
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0answers
47 views

How to solve complex transcendental equation?

a = 22.86/1000; b = 10.16/1000; f = 10 10^9; c = 3 10^8; λ = c/f; d1 = 5 10^-3; d2 = 6 10^-3; λc = 2 a; ...
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1answer
82 views

Help in solve the matrix

I have written the following code. I have two main problems. The first is how to solve the matrix for different Omega, and the second is that if I put letters instead of numbers for k or m, the values ...
3
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2answers
267 views

How to solve a linear system like that

I'm trying to reproduce the following result: with ...
1
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1answer
63 views

How to know when FindRoot[] fails to find a solution

My problem is very simple. Assume you have this piece of code : FindRoot[{x^2 + 1 == 0}, {x, -1, 1}] Now, this code returns ...
0
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1answer
112 views

NDSolve problem with maxit, ndsz, and impsagpg

I'm trying to solve a system of 24 non-linear differential equations using Implicit RK method. My code works perfectly for simple case, i.e., BB=0, but for non-zero BB, Mathematica gives errors: ...
1
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1answer
82 views

Optimizing my code for Broyden's method

The following code is my attempt of employing Broyden's method for root finding on the function $f(x,y)=(e^{xy}-y^2-2,\cos(x+y)+\frac{1}{2})$. Where the first matrix is the Jacobian, then it gets ...
0
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1answer
59 views

FindMinimum for a large range

I have a function functionSL[0.01,zl,zh] where I want to find at which zl its minimum value occurs for each different ...
0
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2answers
36 views

Isolate variable in inequality

I'm having the most stupid of problems. Suppose I have a simple inequality like $$ |2-x|>2.$$ The solution to this is $$ x<0 , \,x>4.$$ This is pretty obvious, though Mathematica insists on ...
0
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0answers
33 views

concept of tangent and residual in AceFem and automation

here trying to solve the pde: ut + ux = 0 in acefem. I have two questions regarding tangent and residual. Tangent shows the s$$ and residual shows ...
7
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1answer
146 views

Solve`DirInf[] — Meaningful value or just a bug?

Bug introduced in 4.1 or earlier and persisting through 12.2.0. or later To the problem below, I get four independent, incomplete solutions, three in terms of ...
3
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1answer
81 views

RootApproximant for a function

DSolve yield this rather lengthy solution ...
17
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4answers
900 views

Find the equidistance curve between two curves

I have three function $f(x)=x^x$, $g(x)=\ln(x)^{\ln(x)}$, $h(x)=\ln(x)^2$ and I want to find (numerically) $C$ the center of the circle tangent to the three curves. I think that one way is to find ...
1
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1answer
85 views

Problem in solving Matrix equation [closed]

can someone help me to find out what is my code problem, I cannot solve the matrix equation ...
0
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1answer
74 views

Numerically solving a system of two equation, one containing a log function

I am trying to solve those equations: ...
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0answers
34 views

Evaluating functions at particular points

I'm a beginner with Mathematica, and I'm running into an issue that I don't quite understand. I define the quantities denom1 = (Sqrt[k^2 + m^2] - p)^2 - k^2 - m^2 ...
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2answers
56 views

Solving equation for unknown and replacing it in second equation

I am new to Mathematica and struggling with its syntax. I have a set of equations, which I would like to solve for my unknowns. I would like to solve the first equation for the first unknown and ...
0
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2answers
65 views

How to create an infinite Table of numbers

I wish to create to generate the set $\{\pm \, 5^n : n\in \mathbb{N}\cup \{0\} \}$ and solve the equation $a+b =c+d$ for all elements quadruplets $a,b,c,d$ in the set which satisfy it. How would I go ...
4
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2answers
225 views

1D mesh generation for PDE solution

I'm trying to solve a system of two PDE that are dependent on time and distance (H[x,t] and P[x,t]). I'm solving the problem using the method of lines but I want to generate myself the mesh and ...
0
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0answers
25 views

Solving quadratic eigenvalue problem [duplicate]

I am trying to solve a quadratic eigenvalue problem using Mathematica similar to Matlab command "polyeig" https://www.mathworks.com/help/matlab/ref/polyeig.html How to do it using ...

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