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

learn more… | top users | synonyms (4)

2
votes
2answers
394 views

Count and plot the number of solutions in an interval

I have equations depending on one or more parameters and I want to find and plot regions in the parameter space in which there is a specific number of solutions. For definiteness let's consider a ...
0
votes
0answers
243 views

Defining extra boundary conditions for NDSolve?

I have a second order reaction / diffusion type ODE of the form $\frac{D_{o}}{r^2} \frac{d}{dr}\left(r^2 \frac{dC}{dr} \right) - \frac{aC}{C+k} = 0$ where $a, k$ and $D_{o}$ are constants and $C$ is ...
2
votes
2answers
639 views

Quadratic programming problem

I am trying to solve a (Sequence) Quadratic Programming (SQP) problem in Mathematica. Here’s the problem setup: ...
1
vote
2answers
306 views

How to pick a solution from a list of solutions using a test?

I have a list of solutions that depends on a parameter b3 and I'd like to get the solution for which the x value is minimal when ...
0
votes
0answers
180 views

symbolic solution for a system of nonlinear equations in mathematica

Would appreciate any help on the following in mathematica I cant figure it out. I have a system of equations that I am trying to solve symbolically. I have 9 equations and 8 unknowns (I have also ...
0
votes
1answer
126 views

InputField equations and Solve

I'm trying to get this piece of code to work: ...
0
votes
1answer
553 views

How to find the zero of a function?

I want to find out when a function has a real root. I first made a RegionPlot3D when the function is zero. ...
7
votes
2answers
465 views

Is there any fast way to solve a quadratic matrix equation in Mathematica approximately?

Let the square nonsingular matrix $M$ is a given convergent matrix. What are the best scalar values for $\alpha$ and $\beta$ (in the real numbers domain), at which the following quadratic matrix ...
0
votes
3answers
219 views

Given a Boolean representation of a system, how can the Reliability Function be displayed as symbolic algebra?

Can Mathematica 9 convert a Boolean representation of an RBD to its symbolic algebraic form? If I have a simple series Reliability Block Diagram made up of 2 components, c1 and c2 bexpr1=And[c1,c2] ...
7
votes
2answers
715 views

Alternate parameterization of a line

There are several ways to specify a line. In Mathematica's graphics, it is done by specifying two points and then connecting the points with the Line command. But ...
0
votes
1answer
62 views

Errors in evalauting an expression

I have the following: Constants: b3b = 2; G = (1/eps^2); a1 = 3; a3 = 4; xc = 0.3; Functions: ...
0
votes
2answers
200 views

Solving Within InverseCDF

I have the following input data: Remove["Global`*"] x = 5/30 // N; y = 0.8; μ = 0.2; T = 5; ρ = 0.8; σ (*to be determined*) And this is the given equation: ...
0
votes
0answers
398 views

Using Solve Within Manipulate to Model Feedback Control System Problem

This post is extremely long and I do apologize - but please bear with me with all the explanation of the context of the question - due to how long the code is I have included a hyperlink where you can ...
3
votes
1answer
259 views

ParametricNDSolve and Constraint satisfaction problem

I am trying to find the values of two parameters that allow for a specific result of my differential equations, under different initial conditions. Given a system of equations: ...
1
vote
1answer
441 views
1
vote
2answers
300 views

Error using Solve on Matrix Multiplication

I am trying to make a function the will find that value of $x$ in the following equation: $x.a=b$ all values of $x, a, b$ are matrices. The dimensions of $x$ are unknown, but $a$ and $b$ have the ...
0
votes
0answers
64 views

Defining functions in a loop [duplicate]

I have a symbolic solution to a linear system with respect to some variables a[i,j] which depend on a parameter t. sol=Solve[...,Table[a[i,j],{i,0,n},{j,0,n}]] I ...
6
votes
2answers
492 views

Very long Refine/Solve batch run - is my code broken, or just complicated?

So I'm trying to run some Mathematica code in batch mode from my university cluster. Specifically, I'm trying to find the equilibria of a system of ordinary differential equations. Inspired by the ...
2
votes
0answers
485 views

I can't solve this set of equations

I am having trouble solving a set of equations in mathematica. I do not get any errors, but i don't get any answers as well. I have some restrictions on my parameters and variables in the equations ...
-2
votes
1answer
1k views

Why can't Mathematica solve these non-linear equations? [closed]

$l_{2}$ and $\theta$ are the variables. All other parameters are constants. I need to find $l_{2}$ and $\theta$ in terms of these constants. $\frac{\mu_{0}\sin(\theta-\theta_{0})}{\sqrt{l_{2}^2 ...
7
votes
0answers
464 views

Creating and using an explicit piecewise function in a convenient way

I have a set of data points that define a function in the form curvePts = {data1,data2,...} where ...
1
vote
0answers
181 views

Having Mathematica solve or help solve a set of 8 equations

There is a set of DDE's that arise in leukemia dynamics and I'd like to find the equilibrium points of the system by setting all of the derivatives equal to zero. The system can be described in ...
4
votes
1answer
197 views

Asking Mathematica to produce a function of some variables

Given $$l_0=\sqrt{\frac{\lambda_1(\lambda_0+\mu_0)}{\lambda_0(\lambda_1+\mu_1-1)}}$$ and $$l_1=\sqrt{\frac{\lambda_0(\lambda_1+\mu_1)}{\lambda_1(\lambda_0+\mu_0-1)}}$$ ...
11
votes
4answers
557 views

How can I find all values of $m$ such that my cubic equation has three different positive solutions?

I want to find all the values of $m$ such that the equation $$-m^3 + 2 m^2 x + (-2 m - 1) x^2 + m + x^3=0$$ has three different positive solutions. I tried ...
4
votes
1answer
204 views

How to demonstrate lack of stability with advection equation

I am trying to that using a coarse grid with an explicit method for, say, the advection equation leads to an unstable solution. The trouble is Mathematica avoids unstable solutions with good ...
2
votes
1answer
127 views

Compact form for domain ranges of many variables

When one sets up an equation to solve one often needs to specify conditions on the variables such as { x>0 && y>0 && z>0 } This is not ...
3
votes
1answer
458 views

Tips for efficiently solving large system coupled (nonlinear) ODEs

I'm trying to solve a system of nonlinear, coupled ODEs, where the governing equation for the $n-th$ ODE is of the form: $\sum_k^M Q_{nk} \ddot{a}_k -\sum_{\ell}^M\sum_k^M S_n(\ell,k) \dot{a}_{\ell} ...
3
votes
1answer
2k views

Finding intersection of two graphs

Here is a toy problem: I have a (directional) line that starts from {2,0} and goes through {1.8, 0.01}. Also I have a ...
-2
votes
1answer
477 views

Interpolating Function inside of NDSolve

I have a problem and it seems to be connected to an Interpolating function inside of an NDSolve command. The resistivity[x] ...
4
votes
1answer
1k views

Use of $Assumptions [duplicate]

I don't really understand the behaviour and the usage of $Assumption. For instance, when I set $Assumptions = λ > 0, I expect ...
0
votes
1answer
42 views

Evaluate a list of Expressions from file

I have a list of expressions in a text file. I would like mathematica to evaluate and export the results at the end of the same file or in a new file. The expressions are in seperate lines in the text ...
1
vote
2answers
517 views

How to make a Dynamic Calculator to solve a quadratic equation?

Taking my first steps in the world of Mathematica Programming. The aim of my program was to modify Wolfram's dynamic calculator (which performs an addition subtraction and a product - in response ...
7
votes
1answer
145 views

Recurrences of lists

Assume we have a multi-dimensional recurrence, e.g. $\qquad\begin{align*} a_1 &= (1,2) \\ a_n &= (1,2) + a_{n-1} \quad, n>1 \end{align*}$ with the easy solution $a_n = (n,2n)$. How ...
0
votes
1answer
272 views

Find root of a function defined as a Module

I have a simple module like BCdet[x_, y_] := Module[ {AuxMat}, AuxMat = Mat /. {f -> x, A -> y}; Det[AuxMat] ] where ...
3
votes
2answers
195 views

Bounds on random number

I have a Markov Chain Monte Carlo code that uses a chi squared function to fit some data. I am running into an issue now with getting unrealistic values for some of the free parameters in the code. ...
1
vote
2answers
411 views

Finding shortest non-zero vector $x$ satisfying $Ax=0 \pmod q$

Let $n$, $m$, and $q$ be positive integers (with $m > n$), and $A$ be a matrix over $\mathbb{Z}_q^{n \times m}$. Using Mathematica, I want to find the shortest non-zero vectors $x \in ...
1
vote
0answers
69 views

Is it possible for Mathematica to give the step by step process of Reduce command? [duplicate]

Input: Reduce[3 x^2 - 2 a x + a^2 - 1 >= 0 && x > a, x] // TraditionalForm Output: ...
0
votes
1answer
133 views

How to simulate a multivariate recursive system from a list

New to mathematica, trying to use Eric Swanson's Pertubation AIM program to solve DSGE models. His code produces a solution as a list or a table. My question is how do I use this list to simulate the ...
1
vote
1answer
136 views
0
votes
1answer
311 views

Solve equation containing conditions (If expressions)

I want to solve the underneath equation. If I try Solve[AAA,dc], then I get no solution. Can anybody explain this? ...
9
votes
1answer
240 views

$1 - \sqrt{5}$ $\in$ $\mathbf{R}$?

Why is there a difference in the output of the following codes? First: ...
7
votes
3answers
472 views

Efficient code for solve this equation

We have $a*b*c=-1$, $\frac{a^2}{c}+\frac{b}{c^2}=1$, $a^2 b+a c^2+b^2 c=t$ What's the value of $a^5 c+a b^5+b c^5$? I tried ...
3
votes
3answers
213 views

Speed up Eliminate

I have a set of trig equations, c1,c2,c3 are constants, I excepted the result is c1 c2 c3 r^2 + (c1^2 + c2^2 + c3^2 - 1) r + c1 c2 c3 == 0 but following code ...
0
votes
0answers
53 views

Degeneracy problem at the start of a series expansion

I am facing the following problem : I have an equation which could write $$ F(x_1(Y))-F(x_2(Y)) = 0 $$ $x_1$ and $x_2$ are the largest and smallest roots of a cubic equation; their definition ...
1
vote
1answer
196 views

FindRoot equation-variable mismatch

I cannot figure out why FindRoot doesn't work and returns this error: The number of equations does not match the number of variables in ... My problem: drawing ...