# Tagged Questions

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

175 views

### strictly positive solution to $Ax=b$

How to find in mathematica one real strictly positive solution, if any, of $Ax=b$. A is rectangular matrix. Thanks
83 views

### nintegrate: greater accuracy possible

I've got the following piece of code: ...
171 views

### Seeking simple function in interval

I am a bit rusty, and struggling to solve this problem. Looking for a simple, well behaved parametric function f[t], from [0,1] to [0,1] such that: f[0] = f0; f[1] = f1; f'[1] = ff1; where -1<= ...
338 views

### How to find roots of a system of equation when number of equations and variables don't match?

I'm trying to check if a system of equations has a solution around a given point, the problem is that I'm using FindRoots and doesn't work when there are a different number of equations and variables, ...
100 views

### Solve an equation for a product

I have an equation a = bcd/fg and I have another one that I can take bcd out of. Easy enough to do by hand, but Mathematica won'...
126 views

### Numerical solution of two equations in two functions

I would like to obtain a solution to the following two equations, where g0[y] and g1[y] are the unknown functions: ...
413 views

### How to solve this Integral equation

D[x[t] - x[t - 1]/(2 E), {t, 3}] + Integrate[E^(-δ)*x[t - δ]/5^t, {δ, 2, 2.5}] == 0 I found solve this problem is hard with Mathematica. I also find a article ...
386 views

### How to put constraints on NDSolve[] solution

Assumed the following example of double pendulum by Thison (Answered by Jens): Animation of double pendulum Imagine that in the given animation(i.e. http://i.stack.imgur.com/p4TgL.gif ), the second ...
191 views

### How to “Control” the Type of Solutions Mathematica Produces Using the Solve Function

Given multiple fractions I am using the Solve function to find the values of the variables $x[1],\ldots,x[7]$ such that the numerator and denominator of each fraction are both 0. I usually have ...
1k views

### This system cannot be solved with the methods available to solve

I know questions about this warning have been posted a thousand times over. But I really couldn't find any solution that worked in my case. It's quite simple: ...
70 views

### NSolve gives {{ x -> #}}, How do I make x = #; I need to use the x value again later

I want to use: demand = {1.92, 2.07, 2.37, 2.72, 2.87}*10^6; NSolve[SetV == demand[[1]]/(Cpf (1 - χ)), χ] I want to make a vector of solutions ...
148 views

### Systems of equations

As I stated in this question I am trying to find the roots of a set of equations. I followed the instructions that the answer gave me and Mathematica gave me the solutions. 1- However whenever I try ...
173 views

### What are the steps using boolean algebra for transforming one equation into another?

I have a special case where I have two equations, which I have solved in a better and quicker way, but I need to solve with Boolean algebra. Using the laws of Boolean algebra, I have to prove that ...
236 views

### How To Replace $\rightarrow$ by $==$ in Mathematica's Output when using Solve

I want to create equations out of the output (solutions) produced by Mathematica when using the Solve functions. For argument's sake, consider the following. ...
117 views

### Multiple dynamic equations for plotting?

Say I have a bunch of equations between variables e.g. h=bcd, i=hce, j=ihbd, ...
138 views

### Non-linear system of equations with a parameter

I want to solve k*x-(x-y)*y^2==0 and y+(x-y)*y^2-(1-x-y)==0 for -10 < k <10 How ...
131 views

### Solving simultaneous systems of linear equations

I have several systems of linear equations in matrix form, and I would like to find the $\vec{x}$ that simultaneously solves them: $$A_1\vec{x} = b_1$$ $$\vdots$$ $$A_n\vec{x} = b_n$$ Is there a quick/...
150 views

### How does Mathematica resolve symbolic systems of inequalities? [closed]

Before getting into my question, let me provide some context: I recently started using Mathematica to automatically perform stability analyses that I previously did by hand. A major part of the ...
315 views

### Solving a large system of nonlinear equations

I have a system of 80 nonlinear equations with 64 variables to solve in Mathematica but it takes a lot of time (about two hours) and then it return "no more memory available" knowing that I have 8GB ...
380 views

### cycloid parametric [closed]

How do I enter 3 parametric equations for cycloids corresponding to circles with radii 1, 2, and 4. I have tried ...
117 views

### How to re-express solution to system of equations after truncating the solution at a given order to give an exact answer

I have a simple enough system of two equations that need to be inverted: ...
243 views

### Help Please : Error in plotting the solutions of FindRoot

I want to find the roots of an equation using FindRoot as a function of a real parameter K and then plot the real and imaginary solutions vs. the parameter K. The function I'm trying to find the ...
48 views

### Resolve not accepting equations involving factorial

If I take , Resolve[ForAll[x,x!>=0],Integers] True But if I make slight modification, ...
151 views

### How to find the Nth zero of a function

It's an almost same question with "a multiple roots finding" but, the order of roots is important in my case. Basically, I'm trying to find Nth crossing point of the following graph: ...
167 views

### How to Map each cell in a matrix to another and solve the system?

tab1 = {{a1, a1 + a2}, {b1, b2*b2}} tab2 = {{2, 5}, {5, 2}} I want to map like this ...
100 views

### Finding an idiomatic way to express a system of linear equations

I have an $n$ x $n$ matrix $T$, where $t_{ij}$ is the element at the $i\,$th row and $j\,$th column, and unknowns $x_i$, $1\leq i \leq n$, where $$x_{n} = 1$$ $$x_{n-1} = 0$$ x_i = \sum_{1\leq j \...
80 views

### Missing solutions for complex equation system

I am currently working on a game-theoretic paper and trying to match two complex best response functions. The equation system includes two decision variables x and <...
96 views

### Trouble representing an equation

I'm having trouble representing the following as an equation ...
329 views

### Simplify trigonometric equation knowing that $\sin(a)=n \sin(b)$

I was working on a problem involving trigonometry. I used Mathematica to help me in solving it. I ended up with this formula: ...
143 views

### Why is ((v k)^-n (k v^n - v k^n))/(n - 1) == b so hard for Mathematica to solve (for v)?

I've tried using both Solve and Reduce. For something that takes maybe 3 minutes to solve with paper and pencil, I'm very ...
890 views

### Equation is solved quickly using Solve but takes too long using NSolve

I have the following simple command to solve for h in an equation: Solve[(1 - 2.25577*^-5*h)^5.25588 == 0.9644952131579817, h] ...
154 views

### FindRoot over a domain, but give domain boundary if no root exists

I call r = x /. FindRoot[f[x] == 0, {x, 0, -5, 5}] f[x] is always monotonic, but sometimes it doesn't have a root in the ...
252 views

### Plotting the results of NSolve as Horizontal Lines

Suppose I use NSolve to find the Real approximations to the intersections of two separate functions over some specified range: ...
98 views

### Why mathematica is not default set to give real solution, instead of complex one? [duplicate]

N[(-8)^(1/3)] gives 1. + 1.73205 i. Since $(-8)^{\frac{1}{3}}$ has three possible solutions, one real and other two are complex. So, why do not mathematica provides all the three solutions, and if ...
182 views

### simulate a 32-bit signed integer overflow in a recurrence function

Considering the following recurring equation: which is this factorial function: I want to find the value of x where f(x) = 0. Actually, the solution is impossible with Mathematica, and it's ...
137 views

### How large can be the dimension of a complex matrix which Mathematica can handle to find its eigenalues?

I have been working with 12 cross 12 complex matrix in Mathematica , I need to work with bigger size matrix of the dimension of the order of hundreds , I was wondering if Mathematica can handle ...
283 views

### Root finding: zeroes of Mathieu function

I am finding the roots of the Mathieu sine function, and find Mathematica and Maple do not agree on the solutions. For example, consider the solutions of ...
108 views

### Solve or preferable Reduce equation

I am new to mathematica and trying to solve and reduce the following: Solve[1 - (1 - p^y)^(u (1 - p)) == a, y] or ...
122 views

### Solve for values which produce negative real Eigenvalues?

Given an n x n matrix "A", with one or more unknown parameters, I'd like to show a plot of which values produce stability (negative Eigenvalues). For example, say you have a simple mass-spring-damper ...
61 views

### Problems solving a differential equation

I am trying to solve a differential equation: $dN/dt = a*N*(90-N)$ with $N(0)=3$ and $N(11)=43$: Using: ...
75 views

### Plotting Multiple Solve Functions

My goal is to plot the functions returned from Solve but assigning each solution to a different function. Here is an example where I do it by hand ...
74 views

### Help inteprete the solution given by reduce

I am trying to solve for a2 in the equation below: ...
104 views

### Unequal behaviour of FindRoot to two similar functions

Unfortunately, I have some difficulties to plot a function. Here is my code: ...
142 views

### handling division by zeros and line equations

today I was writing a code which takes some line equation and a circle equation,finds intersection points that are on $II$ and $III$ quadrants,draw a tangent line to circle from that point and then ...
39 views

### problem on returning value of function as a list using if

today i was writing a function for my project using mathematica that gives a line equation in form of $y=mx+b$ and a circle equation in form of $x^2+y^2=r^2$ and finds the intersection point which is ...
173 views

### How to solve ArcSinh equation for many differents parameters?

I am totally stuck trying to solve the equation below (1/2) x Sqrt[1 + 4 a^2 x^2] + ArcSinh[2 a x]/(4 a) == d Where a and <...
391 views

### High-Precision NSolve

I need to calculate the intersection of two curves f1[x_] := ((Zl ρ ) Exp[-x]) f2[x_] := (α k e^2 /x^2) Where ...
46 views

### Problem with solving an equation [duplicate]

I dont understand why Mathematica cannot solve this equation: Solve[Log[x^2 + 5] + 0.5 x + 1 == 0, x] I get this error message: Solve::inex: Solve was unable to solve the system with inexact ...