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

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0
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1answer
65 views

Dsolve is not solving equation ( 3 system with 2.order diferantial equations) [closed]

I added an image of my equations at the bottom. I dont understand why it is not solving. This is 3 systems with 2.order diferantial equations. I also put my initial conditions. But it is not solving. ...
1
vote
1answer
314 views

Why my differential equations become True? [duplicate]

I've been trying to solve a system of nonlinear differential equation, but the conditions are a bit weird. Two of the differentials equate to the same equation, but have different boundary ...
1
vote
1answer
259 views

Get Cos[2 x] in “Solve”

My goal is to get an analytical solution of x ( $\lambda$ in the problem), when $\epsilon$ (f[x] in the problem) is maximum (use inverse form). I found that if I can use trigonometric identity ...
0
votes
1answer
103 views

Equation in implicit form

This is simple example: v = {1.48622576, 1.53444276, 1.42299438} v/(v + 1) Out[1]:= {0.597784, 0.605436, 0.587288} In the above case expression v/(v + 1) is ...
0
votes
1answer
252 views

Solving a system of equations where two variables can only be one of several discrete values

I want to solve a three-equation system, but I need to constrain two of the variables so that they can only take one of several discrete values that I would specify (this is a circuit design problem ...
3
votes
0answers
113 views

Solving huge equations

I have this expression: $d=-\frac{\sqrt{\frac{780 (f+130) \left(5 d^2 (13 c+f+130)-5 d (c (f+1300)-325 (f+160))+125 \left(2 (2 c+725) f+5 f^2+104000\right)+13 d^3\right) \left(5 d^2 (52 c+17 ...
0
votes
0answers
78 views

Solving an exponential inequality with parameters

Can I use Mathematica for solving the inequality given below? b^(x/2 - 3/2) - b^(ax) - 2c > 0 where b, a, c are the parameters. I want to find out for what ...
-1
votes
1answer
139 views

Mathematica Compute Time Is Extremely Long (Integrate simple function with parameter scan)

I was wondering if you can help. I have a set of equations I need to solve for a list of parameters; entering each parameter value and solving anew each time is simply not economical. I found a way ...
1
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0answers
38 views

How can I select two lists from a list of lists so that I receive the system of equations has only rational solutions?

I want to make a sytem of equations has the form $$\begin{cases} a_1x^2+b_1y^2 + c_1xy+d_1x + e_1y+3=0,\\ a_2x^2+b_2y^2 + c_2xy+d_2x + e_2y+3=0. \end{cases}$$ so that the given system of equations has ...
1
vote
1answer
70 views

Solve never terminates with simultaneous equation set

I have the following set of simultaneous equations that I want to solve symbolically. The two unknowns are $a$ and $d$. $a=\frac{c*(d/10)}{1 + (f/130) + (d/50)} - \frac{a}{1 + (a/100) + (d/100) + ...
0
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0answers
81 views

Solving a single equation with multiple parameters

If I wanted to solve equations like Cos[x]^2 = A Cos[Bx + C] + D what function should I use? The Solve function seems to only solve for as many variables as there are equations. Please note that my ...
0
votes
1answer
216 views

marking the points of x-intercept on a plot

OK, I have a nice plot of some oscillating motion. I can read some stuff off the graph, but I thought it would be cool to show a dot where the curve hits the x-axis and a little label showing the ...
1
vote
1answer
99 views

How do assign an interval of values to a variable in order to use them in a function?

From my code (below) I have K1 and K2 set to zero in order to test this numerical method. However, K1 is on an interval from 0 to 32, and K2 is on an interval from 0 to 8. I would like to know if ...
1
vote
1answer
110 views

A simple expression which Mathematica will not simplify

Sorry for the vague title, but I wasn't sure how to phrase this. I was using Mathematica to solve a fairly simple algebraic equation, but when I tried to substitute the solution into the original ...
4
votes
1answer
253 views

Solving a nonlinear, second order d.e. in Mathematica

I am trying to solve the following differential equation $$ s''(x) = \frac{8}{9}s(x) -2s^2(x) + s^3(x), $$ with boundary conditions $s(-30) = 4/3 $ and $s(30)=0$, in Mathematica by using the following ...
0
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3answers
376 views

How to solve correctly inside a DO loop and then plot

Here is the corresponding code First the equations setup ...
1
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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 ...
0
votes
1answer
159 views

Why mathematica have difficulty solving nonlinear equations? [closed]

I tried to solve this equation via Mathematica: ...
8
votes
3answers
486 views

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

I have a simple lattice / line manipulation: ...
0
votes
1answer
151 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
169 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
281 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
94 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 ...
1
vote
1answer
382 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
578 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
206 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
328 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
38 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
79 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
222 views

How to solve this numerically?

May I ask what is the best way to evaluate ...
0
votes
2answers
103 views

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

Consider the formula for the area of a rectangle. I can write the formula as area[length_, width_] := length*width and plug in numbers for the dimensions and get ...
0
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0answers
50 views
0
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1answer
236 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 ...
0
votes
2answers
119 views

Solving a system of 4 logarithmic equations? [closed]

I would like to solve this system of 4 logarithmic equations in Mathematica. a*log(b+d)=20 a*log(b*30^c+d)=125 a*log(b*180^c+d)=710 a*log(b*360^c+d)=1350 I am looking for the values of a, b, c, ...
2
votes
1answer
74 views

Equation involving hypergeometric functions

I want to solve this equation but nor NSolve nor Solve are able to do this. ...
0
votes
0answers
46 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 ...
2
votes
1answer
1k views

Solving Heat equation [closed]

I want to compute the exact solution of the heat equation but I got an error. u(x,t) (equation of transmition of heat) is the solution of this differential equation: $$du/dt - \alpha d^2u/dx^2 = 0$$ ...
1
vote
2answers
212 views

Mathematica can't minimize a function

Mathematica seems not to be able to minimize this univariate function over integer arguments, $r>2, r \in \mathbb{Z}$. ...
0
votes
1answer
89 views

A question about using Reduce [closed]

Can someone help decipher what is the meaning of this computation that Mathematica has done? ...
4
votes
2answers
430 views

Intersection of Osculating Circle with a Parametric Curve

I have the following Parametric plot Generated from the following: ...
0
votes
1answer
230 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
363 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: http://arxiv.org/abs/hep-ph/9907218v2. Ideally I'd be able to find the smallest value of $x_{n\nu}$ ...
4
votes
1answer
152 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
331 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
523 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
102 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
212 views

Taking the time derivative of a function with more than one variable depending on t? [closed]

Yeah, I was wondering if it was possible ? I have a function which have different variables depending on time, like: $$\frac{d}{dt}mr^{2}\dot{\phi}$$ In this case both $r$, being a length, depends ...
0
votes
1answer
67 views

inverting this equation [closed]

I'm trying to inverse this equation Z = X + X^2 / 2 but couldn't wrap up my head around it. If anyone can provide a step by step solution to this it will be ...
1
vote
1answer
295 views

Solving a System of four equations (with logs) [closed]

I am trying to solve a system of four equations in four variables. I have read a number of threads on similar issues and tried to follow the suggestions. But I think it is a bit messy because of the ...
0
votes
1answer
813 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 ...