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

learn more… | top users | synonyms (4)

15
votes
2answers
3k views

How do I work with Root objects?

I want to solve the trigonometric equation : $$(3-\cos 4x )\cdot (\sin x - \cos x ) = 2.$$ I tried Solve[(3 - Cos[4*x])*(Sin[x] - Cos[x]) == 2, x] It returns the ...
2
votes
4answers
115 views

Using ArcLength in Mathematica 10 using absolute values

With Mathematica 10, I can nicely plot: y = x^2 - 4 Abs[x] - x But I have not been able to use ArcLength to get the length of ...
1
vote
1answer
53 views

Plotting solutions of systems in complex plane

I'm interested in plotting solutions of systems of polynomials in the complex plane, in the following way. Let $f_1,\ldots f_s$ be complex polynomials in variables $x_1,\ldots x_n$. I know how to ...
1
vote
1answer
86 views

Solving ODES in order to find unknown constants

I am trying to solve a set of ODES which represent a second order consecutive chemical reaction. ...
0
votes
0answers
33 views

How to sweep a parameter in an ODEs system using ParametricNDSolveValue?

I want to analyze how my ODEs system behaves when I change only one parameter (in this case d). ...
2
votes
2answers
172 views

Solve ODE in State-space form

Is it possible to solve an ODE in state-space form in mathematica? Such as x'[t]=A.x[t] I attempted ...
-2
votes
1answer
43 views

Using functions inside Solve [closed]

I'm trying to solve a system with the function: Solve. But I am not able to use functions within the Solve, for example the ABS ...
1
vote
1answer
194 views

Defining a curved region for NDSolve

I have an equation to solve using NDSolve which involves two parameters: $en$ and $k$. The equation produces a set of curves when $en$ is plotted against $k$. In ...
1
vote
1answer
335 views

Finding solutions of polynomials system

Let $f_1,...,f_n$ be a set of polynomials in $x_1,...,x_n$ with rational coefficients. I need to check whether a system $$f_1=a_1,...,f_n=a_n$$ has a real solution for large enough count of points. ...
0
votes
0answers
49 views

Reduce does not work

(i*((1 - ((1 + j)^-n))/j)) - (i*t*((1 - ((1 + j)^-n))/j))*(1/((1 + j)^k)) + (1*(1/((1 + j)^n))) == 1 I want to use reduce for ...
1
vote
3answers
94 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
47 views

Integrate equation. Variable in terms of another

This might have an easy solution but I am new in Mathematica. I have an equation for which I want to find the solution. My equation goes like: $$\frac{dr}{dx} = ...
0
votes
2answers
101 views

How to find critical points of trig function over an interval?

I need to find the critical points (maxima, minima and points of inflection) of the function $f(x)= \sin(x)+\ln(\frac{1}{4}x^2-\frac{1}{4}x+\frac{3}{2})$ over the interval $-3\leq x\leq5$. To do this ...
2
votes
1answer
79 views

How to solve for the closed form of this recurrence?

For integers $L,k \geq 0$: $$T(L,k) = \begin{cases} 0 & \text{if }k \geq d, \text{ever}\\ -a_{k} & \text{if }L=0 \text{ and } k<d\\ a_dT(L-1,k+1) - a_{k}T(L-1,0)& \text{if } L>0 ...
8
votes
0answers
159 views

FindRoot kills kernel

Bug introduced in 7.0.1 or earlier and persists through 10.0.2. Fixed in 10.1.0. I'm having problems with FindRoot killing the kernel. In my real application, I want to FindRoot on a black-box ...
1
vote
2answers
109 views

Problems finding intersection points between line and generic function

I'm trying to find Intersection points between a line, which is given by 2 points, and a generic function (I want it to be able to handle polynomial functions, circles/ovals, lines and all ...
0
votes
1answer
49 views

Elements inside arrays seem to be strings rather than signed numbers

When I have code like b = Array[Subscript[be, #] &, {3, 1}] b = b /. {Subscript[be, k_] :> Subscript[-be, k] /; k > 1} I am noticing that Mathematica ...
3
votes
1answer
92 views

How can I solve my easy system of equations?

I am new to Mathematica and am afraid this is a silly question. I have this very easy substitution, it has three equations on three unknowns {w1, l1, t1}. I want to ...
2
votes
2answers
221 views

How to solve this numerically?

May I ask what is the best way to evaluate ...
0
votes
1answer
83 views

In which condition releated to thee coefficients some equation has a solution

Please excuse me if the question seems to commonplace. Can Mathematica give a response to this question: In which condition related to the coefficients $c>0, \, n\geq 2, 0<p<1,\, a>c$ ...
1
vote
4answers
139 views

Solve reports it can't handle my equation

I am trying to solve the following equation Solve[x ϵ + (-ϵ) x^-ϵ - c (-ϵ) x^(-ϵ - 1) == 0, x] Yields Solve::nsmet: This system cannot be solved with the ...
2
votes
0answers
35 views

How to handle solution returned by ParametricNDSolveValue in FindRoot

i was trying to solve a problem relative to root finding in a system of differential equations; here's a simpler case. With two distinct set of parametric differential equations, i'm able to find the ...
1
vote
1answer
63 views

Optimizing matrix inequalities over trace

I need to solve the following problem. Given $n \times n$ Hermitian matrices $A\geq 0$ and $B_1, ~ B_2$ (need not be positive semidefinite), with $Tr(AB_1)<0~,Tr(AB_2)<0$ construct a ...
1
vote
1answer
130 views

4th-order Runge-Kutta method to solve a system of coupled ODEs [duplicate]

I am a beginner at Mathematica programming and with the Runge-Kutta method as well. I'm trying to solve a system of coupled ODEs using a 4th-order Runge-Kutta method for my project work. I have ...
0
votes
2answers
61 views

Defining the domain of positive real numbers

I am trying to solve an equation by assuming that all the variables are real and strictly positive. I can use the keyword Reals for the argument ...
0
votes
1answer
50 views

FindRoot, Loops and multivariate nonlinear system

I posted a question yesterday asking how I could get all the solutions to my system of 4 nonlinear equations with 4 unknowns. I gave up on this since it seems ...
0
votes
0answers
44 views

Any way of solving this system of nonlinear equations with non integer powers?

I have a system of four nonlinear equations. Some of the exponents are fractions. I was wondering if this is what is causing NSolve to run for hours without giving ...
1
vote
0answers
50 views

Why am I getting a conditional output when importing the Dirac Equation to Mathematica? [duplicate]

Just starting out with Mathematica and trying to use the Dirac Equation. I'm working with the following form of the Dirac Equation: $$ i \hbar \gamma^\mu \partial_\mu \psi - m c \psi = 0 $$ And my ...
0
votes
1answer
64 views

Solving a single-variable equation mixed with exponential and algebraic

Trying to solve for x Solve[((a - 1) (1 + d x^2))/(a (Exp[b x + c] - 1)) - e == 0, x] in terms of the constants a,b,c,d, and e. Mathematica says "This ...
14
votes
3answers
2k views

How can I implement the method of Lagrange multipliers to find constrained extrema?

I want to form the function $h=f-\lambda_{1}g_{1}-\lambda_{2}g_{2}$ where $f$ is the function to optimize subject to the constraints $g_{1}=0$ and $g_{2}=0$ so that I can solve the first partial ...
2
votes
2answers
95 views

Only one root at specific interval

I need a help to find k here: $f(x)=-k^x + x^2$ It is not too simple. I have interest to find the single value of "k" where, inside interval {x,2,3}, the function have only one value to x when f(x) ...
1
vote
2answers
114 views

Solving for the limits of an integral

I am trying to get Mathematica to solve for the symmetric limits of an integral of a Square Wave. ...
-3
votes
2answers
96 views

Solving the symbolic quadratic equation ax2 + bx + c = 0 [closed]

I need to ask Mathematica to solve the symbolic quadratic equation ax2 + bx + c = 0. Does it give you the right answer?
0
votes
2answers
45 views
2
votes
0answers
53 views

Simplify large fractions

Hi i'm quite new with Mathematica and i'm experiencing some problems with Simplify and FullSimplify. I'm dealing with a sistem ...
0
votes
1answer
45 views

NSolve taking too long to solve system of polynomial equations

I am trying to solve a system of polynomial equations (10 variables and 10 equations) using NSolve in an attempt to find all solutions. ...
0
votes
1answer
72 views

How to obtain a convergent solution iteratively for a linear system of equations

I am working on a problem that requires an iterative procedure to solve a linear system of equations, the system of equations in matrix form is: $$\underbrace{\begin{bmatrix} r_{11} & r_{12} ...
2
votes
1answer
103 views

Solving for flow speed?

I'd like to use Mathematica to verify the results of a Matlab code that iteratively solves for a flow velocity, u, given some fluid properties and a pressure drop. Ideally, I would like solve the ...
3
votes
1answer
165 views

Very slow mathematica finite differences

I have a simple code which solves an equation by an explicit method (FTCS). It takes mathematica several minutes (mathematica 10.0.2) to finish the calculation while the same code in Fortran runs less ...
3
votes
2answers
180 views

How to propel the integration of time a little bit further? Numerical solution can not evolve to the max time

I try to solve a nonlinear partial differential equation. I obtain a numerical solution which can not continue to the max time I set, I always receive message NDSolve::ndcf: Repeated convergence ...
1
vote
1answer
46 views

Error using NSolve function please help

I have tried to use nsolve to solve this transcendental equation for the bound state of a finite well.. For some reason mathematica is just returning my exact input back to me any ideas on how to ...
0
votes
1answer
90 views

How to solve a linear system of 9 equations with 9 unknowns? [closed]

This is my current code and i'm not sure why it's not working. I am new to Mathematica, though. ...
1
vote
2answers
112 views

Why does this expression take a long time to evaluate?

I was just wondering whether there's an easy to see reason for this expression to take a very long time to evaluate: ...
0
votes
1answer
50 views

NDSolve emitting dvnoarg error [closed]

I'm trying to solve this simple system of ODEs, but it gives me the error "The function v1 appears with no arguments". I've attached a screenshot of the code. I hope someone could help me, I really ...
1
vote
1answer
82 views

Iteration convergence of Newton approximations

I am trying to determine for which initial values Newton's approximation of specific functions (EX: f(x)=x^2 -1)converge and to what numbers it will converge to. *Where Newton's approximations are ...
0
votes
0answers
60 views

Solve Lagrange-multliplier with arrow-security prices with nonlinear (exp) utility function

at the moment I have successfully solved the Demand function for securities in the following model: t=0 current time, 2 uncertain states with same probability in period 2 indexed with i=1 and i=2. ...
1
vote
1answer
181 views

Why won't mathematica solve my two simultaneous equations? [closed]

I'm trying to solve for two unknowns with two equations as follows; ...
1
vote
0answers
70 views

Using Solve without introducing extra variables

First post here. I've tried searching for an answer for this for a few days now, but it seems the search terms (solve, slot, etc) are too generic to be helpful. I'm struggling with understanding how ...