# equation-solving's questions - English 1answer

3.281 equation-solving questions.

### 1 NDSolve coupled Non Linear differential equation, Obtain solution

Trying to solve a coupled differential equations of motion. When there is no Working Precision mention it runs and give following plot for θ[t] but this is wrong, θ must be symmetric about 0. ...

### Solving the equation of motion with Dirac fermions [on hold]

I want solve a system with $n$ equations of motion of the first order. In these equations of motion there are creation and annihilation operators of Dirac fermions. I cannot figure out how to describe ...

### 2 Solving optimal control problem when input is constrained

Given a linear time-invariant system: $$x'(t)=Ax(t)+Bu(t)$$ with initial state $x(0)=x0$ and final state $x(T)=xT$. The performance measure to be minimized is: $$∫_0^Tu(t)^2dt$$ The most important ...

### 1 Plotting equation of error function

2 answers, 59 views plotting equation-solving evaluation
I want plot $W$ vs $t$ ...

### 4 How to easily find the coefficients of a cubic polynomial and its plot for the given 4 points

4 answers, 330 views plotting equation-solving interpolation
Given 4 points as points = {{0, 4}, {1, 0}, {2, -1}, {3, 0}};. I want to find the coefficients of ...

### 2 Non-linear numerical solution with variable parameter

I have solved the following system non-linear: ...

### 1 Problem with solving an optimal control system with Shooting Method

I try to solve a system of differential equation by shooting method. I looked at questions asked on the site but I could not find that could help me. My functions are ; ...

### Analytical solve for biharmonic equation [duplicate]

I want to analytical Solve or numerical solve by Mathematica a biharmonic equation with homogeneous boundary conditions homogeneous? I considered its solution using Fourier analysis, which is not ...

### using power series to numerically solve NS equations of a compressible viscous flow in cylindrical form [closed]

Following this and this questions, I am trying to solve Navier–Stokes continuum equations in cylindrical form for a axisymmetric, compressible and vicious flow using power series. Consider the ...

### 3 How to print all the integer points on and inside the graph of the equation?

4 answers, 136 views plotting equation-solving regions
Consider an equation $(x-1)^2/25+(y+2)^2/9=1$. (x-1)^2/25+(y+2)^2/9==1How can one print all the integer points on and inside the graph of the equation? I ...

### 6 Plot of the Mod of NDSolve solutions sometimes connects discontinuous jumps

UPDATE: The answers given are informative, and provide a workaround which has been given in other posts, but is unfortunately not very efficient. There still seems to be a lack of deeper understanding ...

### 3 Mathematica has trouble solving this coupled differential equation

I'm trying to solve the coupled differential equations: ...

### -1 Why the NullSpace can not find solution when the Det[t]==0

2 answers, 130 views equation-solving linear-algebra
This question contained the problem of NullSpace, but previous ones not. This is a problem seems like my previous one, but there is some details different. I find that perhaps one method can not ...

### 6 FindInstance fails to find integer solutions to glaringly obvious problems

This is a continuation question to Sums as rational vector dot products with a basis constants vector. Consider the following FindInstance query. Looks easy, doesn'...

### Trying to obtain the 2D version of a graph 3D graph

1 answers, 33 views equation-solving graphics
I'm trying to plot this function: f[x_, c_] := 527.5658823401758*(1 - Erf[(2 x - 1)/(2^1.5)]) + 400.6284776272996*(Erf[(2 (-c) + 1)/(2^1.5)] + 1)I ...

### Problems with symbolic expression from Solve[]

I have an equation which is solved by Solve[]. When I define the variables with real numbers, I get an exact solution. However, when I'm trying to use the symbolic expression for the solution, I ...

### 1 The solutions of Det[t]==0 do not satisfy the equation

2 answers, 144 views equation-solving linear-algebra
t is a generated matrix with a parameter kz. Through solving Det[t]==0, the solutions, i.e. kz, are obtained. When I substitute any one solution in Det[t], the result is a large number, why? How to ...

### Use Solve for two Functions to find 1 common Variable

1 answers, 31 views plotting equation-solving variable
I have 2 functions that look like this: F[t_,d_]:= 10+t+2d G[t_,d_]:= 5+t+d I'd like to solve this in such a way to know for which t both Function have the Same value. I assume that this won't be ...

### 2 Convert trigonometric expression into other forms using just a specific set of identities

I am trying to convert a trigonometric expression likesinθ/(1 - cosθ)intocosecθ + cotθor ...