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

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0
votes
3answers
422 views

How to solve correctly inside a DO loop and then plot

Here is the corresponding code First the equations setup ...
1
vote
0answers
23 views

Solving a pair of recurrence relations [duplicate]

Why does this RSolve[{y[t] == a*y[t - 1]}, {y[t]}, t] work, while this ...
10
votes
3answers
524 views

1D quasicrystal: points on a line nearest to points on a lattice

I have a simple lattice / line manipulation: ...
0
votes
1answer
171 views

Solving a system of two equations of third degree

I am trying to solve the following system of two equations for x and y. The solutions for x and y have to be positive and the parameters s and c are positive (to have a coherent interpretation of my ...
1
vote
1answer
192 views

Solution of Coupled Second Order ODEs with Boundary Conditions

D[Tu1[x], {x, 2}] qu - Tu1[x] (fu0 + I w p) == Tou[x] f1 D[T1[x], {x, 2}] q - T1[x] (f0 - b g0 + I w p)== To[x] (f1 - b g1) - g1 For T1 , ...
0
votes
0answers
294 views

Problem with Plot and ParametricNDSolve

This is my first question on this site, I hope it is written in an understandable way. Let's start. My aim is to plot a certain parametric region, with $x$ and $y$ coordinates given by the following ...
0
votes
1answer
95 views

Coefficient of function different than polynomial

My question arise from the problem that Mathematica can't solve the equation $$ \text{Solve}\left[e^{a-x} (0.0299584 a+0.1 b-0.0299584 x-0.152913)-0.9 a+0.9 b+0.9 x+0.18=0.0498614 e^{-x} \left(e^a ...
2
votes
1answer
430 views

How do I get all possible solutions in an underdetermined system? [duplicate]

I have two problems which I'd like to solve with Mathematica. If I have a system of two equations with three unknowns, how can I get to list all possible solutions for the unknowns? Here is what I ...
3
votes
1answer
636 views

Solving a differential equation with initial conditions

I want to get a solution to an ordinary differential equation with imposed initial conditions. I'm confused about why my following code doesn't work: ...
1
vote
1answer
219 views

Solution of an ODE in implicit form

For some non-linear ODEs there is only implicit form of solution using DSolve. For example DSolve[(y[x] + x - 1)*y'[x] - y[x] + 2 x + 3 == 0, y[x], x] gives ...
1
vote
2answers
367 views

Given an equation with one parameter, how do I use NSolve to solve it for many values of the parameter?

I was wondering if there was a way to use the Mathematica NSolve command to solve an equation that has a parameter with various values. An example of which is: ...
0
votes
1answer
40 views

Storing solution to x and y [duplicate]

If I do sol=Solve[{2x+2==y,3x+9==y},{x,y}] then Mathematica will tell me {{x -> -7, y -> -12}} But I would like to ...
1
vote
0answers
85 views

Finding undetermined coefficients with boundary conditions

I have 2 equations which are; To[x_] := c1 E^(-a1 x)/2 + c2 E^(a1 x)/2 + a2 Tu[x_] := c3 E^(-a3 x)/2 + c4 E^(a3 x)/2 Tu equals almost zero ...
2
votes
1answer
224 views

How to solve this numerically?

May I ask what is the best way to evaluate ...
2
votes
2answers
142 views

Solving for any one variable in a formula given values for all the others

Suppose I have an equation relating a number of variables and I know the values of all but one of them. Using the equation and known values as input, is there a simple command (built-in or otherwise) ...
0
votes
0answers
50 views
0
votes
1answer
242 views

Minimize: How to work with specific numeric types

This is a question about the use of symbols in Minimize and how to persuade Mathematica to treat them in a specific way (as integers or rationals) that I have not ...
2
votes
1answer
124 views

Equation involving hypergeometric functions

I want to solve this equation but nor NSolve nor Solve are able to do this. ...
0
votes
0answers
47 views

How to obtain all minima? [duplicate]

If you Solve an equation, you obtain all solutions. But If you NMinimize a function, you only get one minimum. The question ...
1
vote
2answers
237 views

Mathematica can't minimize a function

Mathematica seems not to be able to minimize this univariate function over integer arguments, $r>2, r \in \mathbb{Z}$. ...
5
votes
2answers
476 views

Finding Points of Tangency of a Circle and a Parametric Curve

I have the following Parametric plot Generated from the following: ...
0
votes
1answer
245 views

Numerical Methods - minimum of a function

Problem: The length of the longest ladder that can negotiate the corner depicted in Figure 2 can be determined by computing the value of theta that minimizes the following function: ...
0
votes
1answer
431 views

Trying to solve a transcendental equation involving Bessel functions

I've never used Mathematica before and am trying to numerically solve equation (12) from this paper. Ideally I'd be able to find the smallest value of $x_{n\nu}$ for $\exp(-kr\pi)$ close to 1, and ...
8
votes
1answer
183 views

What are the hidden specifications for FindRoot

The Help page of FindRoot says: "by default, FindRoot uses Newton's method (Newton-Raphson) to solve a nonlinear system" (or a nonlinear equation I ...
1
vote
1answer
380 views

Why does Mathematice dislike my boundary condition in NDSolve?

im trying to solve a PDE-System, with the "periodic boundary condition" c[t,0]==4*c[t,2pi] But mathenmatica says: NDSolve::bcedge: "Boundary condition ...
2
votes
2answers
601 views

Solving simultaneous exponential equations

In[1]: Solve[{(1 + k)^n == 0.6, (1 + k)^(n + 1) == 0.3}, {n, k}] Solve::ifun: Inverse functions are being used by Solve, so some solutions may not be found; ...
3
votes
0answers
109 views

Deciding whether a semi-algebraic set is empty. Which command is best?

[Update] I was able to prove that the "larger" set $ 1\ge x \ge y,w \ge 0$ and $p(x,y,w)>0 $ is empty with another computer algebra system in my slow laptop in few minutes but in Mathematica even ...
0
votes
1answer
895 views

How to find the inverse a symbolic matrix that Mathematica thinks might be singular

I have a square matrix depending on a parameter "a". When "a" has a numeric value (eg 2.1 * 10 ^ 8) through the inverse function Inverse[] I can invert the matrix. If I write the matrix as a function ...
1
vote
2answers
244 views

Symbolic solution of irrational equation

Is there any a nice looking solution to the following equation? eq[x_] := 2 x q1 - 2 q2/x^3 - (4 x^3 q3 - 4 q5/x^5)/(4 Sqrt[x^4 q3 + q4 + q5/x^4]) Better than ...
1
vote
2answers
660 views

Why do Solve, NSolve, and FindRoot all fail on this simple, solvable actuarial equation?

If we express conditional mortality as a vector of annual probabilities of death, like so ...
1
vote
1answer
114 views

Having trouble assigning the result of a Solve to a function

Can anyone see what is wrong with my syntax? It looks like I have successfully assigned the result of Solve to a function. I want Mathematica to return me an numeric value of the function ...
1
vote
1answer
77 views

Invariant error plot for an arbitray system of ODE

i try to use InvariantErrorPlot command for a generic system of ODE but i find only example with pre-building equations from Mathematica Packages. This is one of ...
0
votes
0answers
180 views

Mapping the imaginary axis of the complex (s) plane

In this problem is very difficult to analyze the roots s. Firstly I thought that the problem is in precision, but I am not sure. The criterion which I want to obtain is that one of these roots has a ...
0
votes
1answer
467 views

NDSolve example - analytical vs numerical solution. How to specify initial conditions?

So, I have the following equation: y[t]^-3 == w^2 y[t]/t^2 + y''[t] where w^2 = (t0 k0)^2. Analytic solution is easy to ...
0
votes
1answer
659 views

Solve non linear system of equations

I am trying to solve a system of two equations with two unknowns. In these equations I have, a part from constants: Unknown nr 1, $$D_{\perp}$$ Unknown nr 2, $$\omega_C$$ Known function of r: ...
0
votes
1answer
132 views

Numerical method for solving a polynomial equation

I am looking for a numerical solution of a equation which contains, in general, one polynomial equation with unknown variable x. I have tried Reduce, ...
0
votes
2answers
123 views

How to get a number from Solve [duplicate]

It's often useful to get just one number from Solve. I use the following construction for acquiring one solution from the expression returned by ...
0
votes
1answer
119 views

How to Solve/NSolve/Reduce this rationalized equation

In this problem I don't know why the system is not solvable. I have just one unknown K0. ...
0
votes
0answers
111 views

Solving for a variable within a definite integral using FindRoot

I want to solve for P in this equation: Integrate[1/((P/(M*V)) - r*g - c*A*(V^2)*p/(2 M)), {V, 0, 26.82}] = s , where all constants are given except P. I've ...
-6
votes
1answer
189 views

Poincaré section for 3BP

I try to plot the Poincaré section for the 3BP i use the following code that works very well: ...
0
votes
0answers
76 views

How to solve an inequality

I am trying to solve the following inequality: Assuming[{R[k] >= 0, R[k + 1] = R[k] - 2^N Y, Y >= 0 && N >= 0}, Refine[Re[R[k + 1] >= 0]] I ...
1
vote
2answers
350 views

intersection between function and plane

I try to solve a ODE system of equations and i want to plot the intersection of the 3D solutions with a costant plane. To do this i use the follow code: ...
0
votes
1answer
64 views

NSolve or Reduce for obtaining the results and connecting roots

Here I have one problem how to solve numerically equation for different values of one parameter x. I used just two digits because of length, but for x=0.57 I should have one real root and for others ...
0
votes
0answers
146 views

Boundary Condition Problem with Green's Function

My temperature distribution looks like: Mean wire temperature is : To[x_] := 2 c1 Cosh[x a1] + a2 And it is continuous at two points. In positive part: ...
1
vote
1answer
941 views

Why Mathematica can't solve this? NSolve or Solve

I want solution of x and y which should be positive real numbers ...
2
votes
1answer
559 views

2d heat conduction equation: Boundary and initial conditions are inconsistent

I have the following code for a 2d heat c equation: ...
0
votes
1answer
68 views

Solve equation with two different sets of replacement rules

I want to solve eqn for c0. I want to do it with both replacement rules. I realize I could just use solve twice, once for subsCoke, and once for subsPepsi. I'm trying to do it in just one Sovle to ...
0
votes
1answer
244 views

Why can't Mathematica solve this system of equations?

I am trying to solve the following system of equations for three unknowns Theta, Nu, and K. All the other parameters are constants. The third argument in Solve, ...
3
votes
1answer
123 views

How to transform an equation so that the coefficient of a certain term becomes 1

Say I have an equation like A + 5 B + 10 C == 0 and I want to have Mathematica write this as (A/5) + B + 2 C == 0 i.e., I ...
3
votes
1answer
647 views

Why is Solve returning an empty list?

I evaluate ...