# Tagged Questions

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

1answer
41 views

### finding the coordinates of intersection point of two complicated implicit function [duplicate]

I have two complicated functions and i plot the contours of them like this: ContourPlot[{f[x,y]==0,g[x,y]==0},{x,x1,x2},{y,y1,y2}] I would like to find ...
0answers
75 views

### Gauss-Jordan program in Mathematica

Hi to everyone I made this program to solve a linear system by Gauss Jordan, this is my code to solve the system: ...
1answer
59 views

### Nested double sum does not converge

I am quite a beginner, and have the following problem. I have a sum that comes from Poisson distribution and for each index there corresponds a binomial-type sum. I try to find its root for the ...
1answer
52 views

### Solving biharmonic equation with Mathematica

I would like to solve a biharmonic equation in polar coordinates of the form: $\Delta \Delta \Phi[r,\theta] = r^i cos(j \, \theta) \quad i,j \, \epsilon \, \mathbb{N}_0$ I know that a solution for ...
0answers
46 views

### Solving a non-linear equation [duplicate]

I have one non linear equation, and I am trying to get value of x but when i employ Solve function as below ...
3answers
78 views

### Issue finding roots in a polynomial [closed]

I am trying to find the roots of the polynomial (-2 + x)^3 (-2 + x^2) (-4 + x^3) (4 + 2 x^2 + x^4) (-8 - 8 x - 2 x^2 + x^3 + x^4) . I am using the command ...
4answers
322 views

### How to solve an equation with a nested function

I have the equation f[f[x]] == 28 + 9 x How can I solve this for f[x]? I note that this post relates to the topic, but ...
0answers
67 views

### Solving an equation entered by the user via the Input function

I am new to Mathematica. I am trying to create a program that takes in an equation from user input and then gives the answer. I started with a manipulate function as I created a similar program for ...
2answers
56 views

### Plotting the results from Solve in a Manipulate expression

I am a self-taught Mathematica user, trying to make some progress. This is my code: ...
2answers
92 views

### Find smallest solution in Solve's solution set

When an equation has multiple solutions, how do you find the first solution? Example: Say we're trying to find the first positive x-intercept of the cosine function: $cos(x)=0 \land x \ge 0$ ...
2answers
73 views

### Error In polynomial Root Finding

I have a polynomial in y like so: 2.00855*10^20 + 6.89796*10^20 x y + (5.17347*10^20 + 5.92241*10^20 x^2) y^2 - 1.4806*10^21 x y^3 + 7.77316*10^20 y^4 == 0 I ...
2answers
146 views

### Solving equation containing ArcTan terms

IN MY EDIT I DESCRIBE HOW I GOT TO THAT EXPRESSION AND THE ORIGINAL PROBLEM. I have this expression: ...
0answers
61 views

### Solve equations involving summation expressions in Mathematica

I am trying to solve the simple linear regression equation analytically in Mathematica (not using builtin functions). I managed to calculate the gradient as follows f is loss function using RSS and ...
1answer
62 views

### Why is FindRoot failing to evaluate this function? [closed]

I have a (somewhat long) script which runs cleanly until the very last stage. Here, I'm using FindRoot to attempt to parameterize implicit curves in the zero set ...
0answers
60 views

### Numerically parameterize portion of $F[x,y]==0$ [duplicate]

I have a relatively complicated function of two variables F[x,y] whose zero locus contains a number of intersecting paths in the $x,y$-plane. A problem I've been ...
1answer
64 views

### Automation of Perturbation Solution

I'm trying to solve an equation of the form $$R(\theta)f(\theta)+hg(\theta) = 0$$ for small $h$, where $R$, $f$, and $g$ are functions. I've assumed a power series expansion for $\theta$ in terms ...
1answer
248 views

### Reduce a complex inequality

Reduce[Abs[1/(1 + I/Sqrt[α])] < 0.5, {α}] It is taking long time to run. Can any one help me to get the reduced condition in terms of $\alpha$ or its modulus. ...
2answers
77 views

### Using solve on conditional functions

I know that the code is pretty long, but most of it is just defintion. Do you see why the Solve gives me "his system cannot be solved with the methods available to Solve" back? ...
1answer
173 views

### How can I combine NDSolve[] with NSolve[]

Consider the two below ODEs with following dependent B.C. In the boundary conditions $k$ is an unknown. $$y_1''(x)=x$$ $$y_2''(y)=0$$ $$y_1(1)=y_2(1)$$ $$y_1(-k)=y_2(-k)$$ \frac{\text{dy}_1(1)}{\...
1answer
83 views

### Matrix equations solving

can you explain me the easiest way for solving this matrix equation? I have this matrix: a={{-4,1,3,0},{-2,7,1,-1},{1,-1,9,-3},{-1,0,5,-10} and the Equation is: ...
1answer
89 views

### Precision of FindRoot

Consider the following code: ...
0answers
66 views

### Avoiding divide by zero to simplify an expression enough to solve

I have a very complicated expression that I'm trying to set to zero and solve. I simplify by substituting in variables, but Mathematica isn't fully simplifying it -- my guess is because it thinks it ...
1answer
72 views

Define: ...
2answers
39 views

...
0answers
63 views

### Why can't Mathematica solve this complex equation?

So I want to find the complex part of Rthev,equate it to zero and solve for ω but it won't let me. Is it because it thinks ...
1answer
80 views

### How can I solve a set of equations with variables and eliminate a few variables at the same time?

I just started learning Mathematica since I needed for my current research. I'm trying to solve a set of equations with different variables, eliminate a few variables in the set, and express one ...
2answers
87 views

### Determining the value at which a function becomes non-real or undefined

If I have a function $f(x)$ that I only know numerically and that returns a real value for some range of values $-\infty < x \leq a$ and complex values for $a < x < \infty$, how can I ...
1answer
44 views

### Solve matrix equation for matrix

Is there any function like Solve but designed to deal with matrix equations? Something like: ...
1answer
105 views

### Evaluate an integral with parameters

I already asked this on stack overflow but was redirected here. I am trying to solve the (highly non-linear) following system of equations : with and $g_0$, $\Lambda$ are positive constants ...
0answers
40 views

### What is the default method used by NSolve

I have a system of 6 polynomial equations of the form aijk xi xj + bik xi = ck (k=1,2,...,6; summation convention on i & j) I am using NSolve[{eq1,eq2,...,eq6},{x1,x2,...,x6},Reals] What ...
2answers
71 views

### solve system including piecewise function

I've read posts about how to do this in a direct way, but the method doesn't work for my simple system? -- see code: ...
1answer
55 views

0answers
86 views

### Solve equations with Monte Carlo [closed]

I am dealing with a complicated problem. I will use a simple problem to explain it. I have two variables x and y, and two equations: x+y=A 2x+y=B The value of A and B is determined by measurement, ...
2answers
166 views

### Solving Boolean equations

@Artes suggested this code to me to solve this system of equations: ...
2answers
103 views

### Solving and Plotting Infinite sums over solutions to transcendental equation involving Bessel functions

I am trying to use Mathematica to plot the following equation $E(q,\Delta)$ vs $qa$, for set values of $D \Delta/a^2$ and $\bar\rho a/D$. I have looked at other stackexchange posts which deal with ...
1answer
68 views

### Stopping NDSolve when encountering stiffness

I am solving a differential equation for different initial conditions using ParametricNDSolveValue. I need to look at the value of the solution at some later point, ...
1answer
44 views

### Probems using 2 For and a AppendTo to cycle through my Equation to solve some matrixes

I am trying to solve a few problems here. I have an equation with multiple variables that I am trying to solve in For loop method. I will attach the file below. In addition I am trying to get it to ...
1answer
22 views

### build absolute value equations know solution [closed]

We have absolute value equations with unknown coefficients: |x + a| = b and we know solutions: x = 11 and x = 5 We need ...
1answer
52 views

### Finding an Integer, Unimodular Matrix that connects two given matrices

I have two symmetric, integer matrices, $K$ and $K_2$ which have the same determinant and the same signature (number of positive - number of negative eigenvalues). I want to find an integer valued ...