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

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1
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1answer
241 views

NSolve fails to solve a nonlinear equation

Mathematica can not solve this: g = 9.82; ω = 0.5; h = 5; y0 = 1; v = 0; τ = 0; NSolve[h + v t - (g t^2)/2 == y0 Sin[ω t], t]; The error code is: ...
1
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1answer
203 views

NSolve on bounded domain

I don't expect NSolve[] to be able to obtain all solutions in generalfor example. In principle there should be an algorithm that finds all solution to $f(x)=0$ for ...
0
votes
1answer
91 views

How to solve this equation? or get the numbers of solutions of the function?

I have a function like this.. $$ f[k]=\int_0^\infty Exp[-ax]x(Cos[bx])^{2}BesslJ[0,kx]dx $$ I want to know how many local maximuns this function has.. So I try to get the derivative of f[k] $$ ...
0
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1answer
159 views

Plotting an extremly large output

I'm trying to plot the solutions of this determinant: ...
3
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4answers
232 views

How to merge permutations obtained from Solve on multiple variables?

When I compute the following expression to find integer solutions of the equation (x^2 + y^2 + z^2 == 14^2) ...
1
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1answer
81 views

How to solve these equations by Mathematica?

l tried it with Solve,DSolve and NDSolve functions,but all failed.Should l simplify the equations in the papers or use other mathematica functions.Thanks~
2
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3answers
214 views

NSolve & PrecisionGoal

I am using NSolve to find numerical solutions of a particular equation. I do not need the solutions to as high of a precision as the other numbers in my notebook. To improve run time (I am iterating ...
0
votes
1answer
227 views

NDSolve with initial condition: initial conditions did not evaluate to an array of numbers of depth 1(for 1D) or 2 (for 2D) on spatial grid

I have the following naive code to solve a PDE in two spatial dimensions (x,y) with periodic boundary conditions: ...
1
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2answers
82 views

Solutions to multivariate equation

Is there any way to get Mathematica to give a set of solutions (pairs of x and y that are integers) to an equation with multiple variables? Something like: ...
2
votes
1answer
153 views

Computing Poincaré symbolic solution for an arbitrary integer order polynomial

In the 1880s, Poincaré created functions which give the solution to the nth order polynomial equation in finite form. These functions turned out to be "natural" generalizations of the elliptic ...
1
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0answers
104 views

Equation solving: Solve returns a periodic solution

I have a very simple trigonometric equation, that I've been trying to solve for a variable for a few hours now: (I couldn't find how to correctly format this) ...
0
votes
0answers
221 views

Solving a system of equations involving partial derivatives for a wave

Before saying anything about the problem, I have checked "How to solve a system of partial differential equations?" yet it does not actually answers my question, as I have a 10x10 matrix to work on. ...
0
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1answer
206 views
0
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1answer
121 views

Why does this work with Wolfram|Alpha but not Mathematica? [closed]

I ran into this while doing some work today: It's the exact same syntax - and I expected that Mathematica would be more likely to be able to solve it, since oftentimes Wolfram|Alpha doesn't have ...
0
votes
0answers
45 views

Initial values/parameters in equation system of dimension 32

This is a system of equations of dimension 32, that describes an economic system. I want to find a set of parameters and initial values in which the system can be solved, and solve the system of ...
1
vote
1answer
62 views

Characterising the set of parameters that satisfy a system of non-linear equations

I am looking for a solution to the following problem and could not find an answer so far. I have a quintic equation, $f(x;a,b,c,\cdots)-x=0$, where $x$ is the variable with respect to which I need the ...
1
vote
1answer
211 views

solve recursion equation with condition

How can I find $f(x)$ in terms of $x$ in the following equation? $ -k\, x \,f(x) + k \, (x + 1)\, f(x + 1) - r \, f(x) + r\, f(x - 1) =0$ $r$ and $k$ are constants and $f(x)$ should satisfy: ...
0
votes
2answers
101 views

Very slow solve and problem when solving in a nested for loop

I am using a nested for loop to solve a system of equation for {a, ga} for 2 varying parameters: here it's rm and sig. ...
5
votes
2answers
841 views
0
votes
1answer
507 views

Problem with FindRoot applied to functions

I am having difficulty with the error "is not a list of numbers with dimensions..." when using FindRoot (and other numerical routines in Mathematica) to solve equations numerically when the argument ...
0
votes
0answers
58 views

Enormous and unclear output when using Solve

After running for about 30 minutes the program yields the below-given unclear output (of course I didn't copy the whole output, only a small part of it). So it explicitely gives 3 possible solutions ...
0
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0answers
97 views

Selecting values over lists for discrete inputs in NDSolve [duplicate]

I'm currently trying to simulate a step response in a simple tank system with NDSolve. I would like it to start at say time 2 (the precise time is not important). ...
0
votes
1answer
84 views

Solving a complicated system

Could anybody please make a suggestion how can I implement this program which attempts to solve $2$ dimensional complex system of equations? My computer is not able to solve... After 3 hours the ...
2
votes
1answer
93 views

How to obtain numerical answer for equation containing integration

Could some one tell me how to obtain numerical value of $a$ and $b$ from equations below: $$\frac{1+exp(b)}{1+exp(0.9a+b)}=0.95$$ $$\int_{0}^{\infty} \frac{1+exp(b)}{1+exp(a x+b)}=1$$
2
votes
0answers
200 views

NDSolve is running an extremely long time: how can I save the existing data?

I am trying to solve a PDE by the following code. It takes 1 hour or so to reach t=25.72 but about 20 hours to reach t=25.72404031638060174049337306126853310997. Actually, the time step is extremely ...
2
votes
0answers
139 views

Proving large inequality in 6 variables

I have arrived at a very large inequality in 6 variables that I would like to prove is true. The command I have tried is the following: ...
4
votes
2answers
169 views

How can I get all solutions of a system of equations with Reduce?

The post What is the difference between Reduce and Solve? discusses the difference between Reduce and Solve. Now, with the ...
3
votes
1answer
280 views

Fick's Law over Implicit Regions

I'm trying to solve 2D Fick's law of diffusion from the boundaries of a triangle (future shapes will include more complex implicit regions). I'm able to model diffusion without time in complex ...
1
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1answer
141 views

Defining Solutions to FindRoot a functions of parameters-Part II

Here's a similar question as the the preceding question with the same title, but this time with vectors, which I need to use. I followed the suggestion in the answer the the previous question, but it ...
0
votes
1answer
80 views

Weird behavior when solving a simple physics problem

I have the following code in Mathematica that represents two balls being thrown, one with a velocity v10 (6 in this case) and another ball thrown with a velocity v20 (its just dropped) one second ...
1
vote
1answer
311 views

Defining solutions to FindRoot as a function of parameters in Mathematica

This works: f[a_] := x /. FindRoot[x^2 - a == 0, {x, 1}] f[3] (* 1.73205 *) I need this to work, but it doesn't: ...
0
votes
2answers
102 views

How to exract the roots from “Roots”? [duplicate]

Given how the output looks like, as in a set of "==" assignments, is it possible to extract specific roots from the output of, http://reference.wolfram.com/language/ref/Roots.html ? And then do a ...
0
votes
1answer
1k views

How do I write nested for-loops?

Looking through the reference.wolfram, I couldn't see an example of how to write a multiple line "for" loop in Mathematica. I need to nest many for-loops in such a way I can do many things in the ...
1
vote
0answers
76 views

Why do I get this error (solving a system of equations)? [closed]

I use the following code ...
0
votes
2answers
177 views

How to contourplot a function defined via findroot? [duplicate]

when I use contourplot, the system will simplify the expression first with its parameters holded. However some expressions can not be simplified first without inputting parameters, for example, ...
3
votes
1answer
194 views

Solving Non-linear System of Equations

I need to get a symbolic solution to a system of non-linear equations (equation 8 is non-linear), but Mathematica is running for ever and gives no answer. Is there another way to get the solution? My ...
4
votes
1answer
153 views

How to reduce a quartic form to a quadratic form with equal roots

Preface: To clear the theoretical background this question is cross-posted on math.stackexchange here. I have a polynomial in $n$ variables of the form ...
5
votes
1answer
185 views

Solving 2-D Mechanical Systems

I'm trying to use Mathematica to solve a particular 2-d mechanical system. The system comes from "DESIGN AND OPTIMIZATION OF AN EIGHT-BAR LEGGED WALKING MECHANISM IMITATING A KINETIC SCULPTURE, “WIND ...
0
votes
2answers
102 views

Solving a system of two equations

I have a system of two equations with the variables T and X that I tried to solve: ...
1
vote
1answer
132 views

Fitting with roots of transcendental equation

I'm new to this community and my first question probably reflect my lack of confidence with Mathematica. My problem is the following: I find the roots of a transcendental equation dependent on a ...
-3
votes
1answer
126 views

How to make X and Y = Z? [closed]

Hello I have a big question, maybe it's extremely easy but for now I'm unable to make it work. I'm a programmer and what I need to do is for example: if X = 2 and Y = 1 then Z = 1 if X = 3 and Y = 1 ...
0
votes
0answers
75 views

Computation doesn't Finish

I'm trying to solve some problem by the following code: ...
-1
votes
1answer
112 views

Find $r$,in terms of variables $U$ and $V$

I want to solve this equation, for $r$: ...
0
votes
1answer
365 views

How to solve Mod equation with mathematica [closed]

i'm pretty noob with mathematica but i need to solve an equation: $$c\equiv m^2\pmod n$$ I tried something like ...
1
vote
0answers
58 views

Input `Reduce[Mod[a + x, l] == 0, x]' and output `x == -a + kl`?

Reduce[a + x == k l && k > 0, x] (* k > 0 && x == -a + k l *) I think a + x == k l and ...
0
votes
1answer
59 views

How can I solve a difference-differential equation with new variable? [closed]

I want to ask how we can solve this equation: $$ xyy' = x^2+2y^2 $$ I tried with new variable $$u=y/x$$
0
votes
1answer
246 views

solve equations with high degree

this is my code,i want to solve this equations.can anyone give me some help about this,wheather mathematica can solve this.thanks a lot ...
0
votes
1answer
97 views

If domain Reals specified all constants should be real? Problem with Solve

I've got a problem solving an equation. I want to solve: Solve[Arg[h]==0, r0, Reals] with h being some imaginary number ...