Questions tagged [equation-solving]

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

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0
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3answers
63 views

How do I plot a function that is in a list? [closed]

I am trying to plot a function that I had converted from the returned list of rule assignments from Solve[ ]. I am trying to plot this, but the resulting graph is empty. Does anyone know what I am ...
0
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2answers
40 views

Finding the solution for argument of interpolating function for known functional value

Suppose I want to numerically determine the location of an object falling vertically in a gravitational field from an arbitrary height h. I know that I can use <...
2
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2answers
66 views

Hyperplane equation coefficients

I am stuck to this very simple problem, on paper, but I cannot see a way of having Mathematica giving me the coefficients of a hyperplane equation given n+1 points ...
0
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1answer
61 views

NSolve connot solve my equation [closed]

I'm trying to solve $$\left(\frac{hc}{k_B} - 5x\right)e^{hc/k_Bx} + 5x = 0,$$ where $h = 6.626 \times 10^{-34}$, $k = 1.381 \times 10^{-23}$ and $c = 3 \times 10^8$. My code is ...
3
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0answers
70 views

How to improve this code?

The aim of my work is to find a value for the complex constant $\omega$. In order to do that I solve the below system of differential equations with a manual shooting method: I first solve the system ...
1
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4answers
145 views

Solving radical equation

Intro I have encountered two radical expressions for which I have to find the roots analytically: ...
0
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0answers
55 views

Search for roots in numerical solution of CoSODE

Is there a way to find out the roots of the system numerically? For the toy model described by the coupled second order differential equation (CoSODE), $a\ddot{x}-cy=0$ $a\ddot{y}-cx=0$ the solution ...
1
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1answer
52 views

DSolve a partial differential equation with two boundary conditions

While trying to solve: $$ z \frac{\partial}{\partial z} (z G(s,z))=z \cosh (s) \frac{\partial}{\partial z} G(s,z)-\frac{1}{2} \sinh (s) \frac{\partial}{\partial s} G(s,z) $$ using DSolve it gives a ...
1
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1answer
95 views

How to impose initial condition for a duration of time?

A reaction diffusion system contains 2 pde, $xc, xp$, and one ode, xnn. A variable in my coupled pde system, $xc(t,x,y)$, has a piecewice initial condition for a duration. I am trying to redo the ...
3
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2answers
211 views

How to find intersection points of several circles in Graphics without using Solve[ ]?

For example, I randomly plot some circle in Graphics[]: ...
0
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2answers
66 views

Solve nonlinear equation

Please help me to solve the following nonlinear equation, such that I used ''FindRoot" but no result the equation is ...
4
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2answers
217 views

How to determine a limit of integration from a known integral?

I have an integral equation for a value t between the limits of integration 1 and a parameter u. I am trying to solve for ...
4
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2answers
154 views

Not getting the correct asymptotic behaviour when sending a small parameter to zero

I want to solve this equation for $z$: $-\frac{2\pi^2}{\beta^2}z^2+\frac{2i\pi^2u}{\beta^2}z^3+z^4=0$ $\beta$ is a positive real constant, $u$ is a real variable ranging from $0$ to $2\pi$. The code ...
0
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1answer
53 views

Solve for not y = 0 but for y = n [closed]

Let’s see if I manage to explain this well enough. I need to find roots of an equation(let’s say a quartic) but not at the points where the slope crosses the $x$-axis (y = 0), like the ...
2
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2answers
111 views

Can I calculate the reciprocal of a harmonic series in wolfram mathematica?

hello this way is how you solve an harmonic series in mathematical. with the first 10 values Sum[1/n,{n,1,10}] # solution is 2.49 i want know how to do it this if ...
0
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1answer
53 views

findroot multiple variables

I have an equation 811*a + 741*b + 1025*c + 752*d = 94508.16372 How can I find the possible roots of a b c and d in specific scopes? I tried ...
1
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1answer
73 views

Problem finding roots [closed]

I am trying to obtain numerically the roots of a function, but Mathematica is not able to obtain them. I used NSolve, FindRoot and even the custom Jens' findAllRoots function, but none of them work. ...
2
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2answers
112 views

Real roots of an infinite series consisting of Harmonic number

I know that the following equation, as a function of $s$, has two real roots: $$ \sum_{n=1}^{\infty}e^{s(1-s)H[n]}=\frac{1-r}{r}e^{s^2}-1 $$ for $0<r<1$. Is there any simple way to find these ...
4
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2answers
131 views

Numerically solve PDEs with constraints and without boundary solution

I have a PDE like D[h[x1, x2], x1]*a[x1,x2]+D[h[x1,x2], x2]*b[x1,x2] + c[x1,x2] == h[x1,x2] s.t. gradient(h(0,0))==0 where a,b,c are known functions of x1 and x2, ...
1
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3answers
58 views
0
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1answer
65 views

Solving a simple functional equation [closed]

As a newbie to Mathematica, I am currently trying to test what are the software capabilities and limitations. Thus, I have reached the following problem. What I want to do, is to construct a ...
8
votes
3answers
615 views

Ignoring fractions can lead to correct answer

There is a curious example in Posamentier's book "Magnificent Mistakes in Mathematics" (p. 72): $(7+3/7)*(4-3/13)= 7*4=28$, where cancelling the fractions leads to correct result. If we ...
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1answer
32 views

solve for variable in iterator limit

Why can we not solve for P in the iterator limit in the problem below? How can it be solved? ...
3
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3answers
499 views

How can I solve a system of linear equations? [closed]

How can I solve this system of equations in Mathematica? ...
2
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1answer
120 views

Neumann boundary condition ignored

Im trying to solve a system of two PDE (im[t,x] and ia[t,x]) that are dependent on time and distance. I’m using my own anisotropic mesh (thanks to @TimLaska) that is aimed to represent an interface ...
1
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2answers
59 views

Approaches to expression reduction

I am still learning how to use Mathematica more efficiently, but something that I keep bumping into is problems with it reducing formulas. Often, I'll ask it to compute a certain formula (take a ...
1
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1answer
139 views

How can I solve a system of PDEs with constraints but having unknown boundary conditions

I have a 1st order system of two PDEs with two independent variables and two dependent variables. ...
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1answer
104 views

Solving an equation with Reduce

In the equation shown in the code that follows, I must find or eliminate rb, but Mathematica is reluctant to work with my Reduce ...
-1
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1answer
77 views

How to make NSolve faster?

Can somebody help me, to make these program faster? u and r are parameters, a,b,c,d,q,w,Ca are variables. I need to numerical solve these system for many values of u and r. And it take 10 seconds for ...
1
vote
1answer
87 views

How to manipulate multiple solutions to equations while keeping variable names?

relatively new to Mathematica, but couldn't find an answer online for how to do this more cleanly. I am solving these equations in six variables that give me a number of solutions, which are given as ...
1
vote
1answer
80 views

How can I find all solutions of this equation?

I am trying to solve this equation with integer solution $x^3 + (x + 1)^3 + (x + 2)^3 + (x + 3)^3 + (x + 4)^3 + (x + 5)^3 + (x + 6)^3 + (x + 7)^3 = y^3.$ I tried ...
0
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1answer
29 views

Perform Eliminate, Solve and Format at once in Mathematica

I have a series of equations where I use eliminate to get a new equation with desired variables. This equation is then solved for a specific variable and then the result is presented in a specific ...
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0answers
53 views

Solve method in Mathematica, symbolically solving method

I am looking for a way to solve this equation symbolically with Mathematica. ...
2
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2answers
98 views

Returning a custom value rather than {} when Solve finds no solutions [closed]

I have the following code: n /. Solve[ {c == 1/2 (-2 + 3 n^2) (-1 + 3 n^2) (1 - 3 n + 3 n^3), n ∈ PositiveIntegers}, n ][[1]] This restricts ...
4
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2answers
299 views

Roots given by Solve are not satisfied by the equation

I am finding roots of a polynomial equation using Solve. However, two of the five roots given by Solve do not satisfy the equation. Here how I do it: ...
1
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0answers
44 views

NDSolve - interpolation or machine precision problem

For the following equations; $$\begin{align} \frac{\partial \text{NN}(t)}{\partial t}&=-\frac{(c \times\text{Sigma})}{\pi\times L\times \text{Omega}^2} \text{NN}(t) \times\text{Phi}(t)-\frac{\...
1
vote
1answer
181 views

How to code this iterative process?

I am facing difficulty to realize this double iterative process. The equations in question are The flow chart for the iterative process is given as The different parameters are defined as ...
1
vote
2answers
57 views

Problems with Dsolve[] and simple function

I'm trying to solve the following very simple differential equation, but it seems Mathematica cannot give me an answer, ...
4
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3answers
160 views

Initial-boundary value problem of 2nd order linear PDE with variable coefficient

Today I was studying partial differential equations and I tried to check if my solution was correct, I thought Mathematica code would be easy, but it wasn't. Here is my problem: Solve $u_{xx}-2tu-u_t=...
9
votes
5answers
509 views

How do I find complex values that satisfy multiple inequalities?

I want to find $a,b \in \mathbb{C}$ such that $$|1-2a-2b| < 1 \quad \text{&} \quad |1-2a+2b| < 1$$ using mathematica. I tried to use ...
2
votes
1answer
66 views

Trying to solve non-linear coupled differential equation with boundary conditions at different points

I'm trying to solve systems of dif. equations with boundaries conditions at distinct points such as: ...
1
vote
1answer
89 views

Find instance of equation that also minimizes one variable

I want to find an instance of solution of a very complicated equation like func[a, x, y, w, z] == c that is a global minimum (within the solution set) of a. Below ...
1
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3answers
95 views

NMinimize with four equations for four points [closed]

The following is an unsuccessful attempt to pass a parabola through four points. ...
2
votes
2answers
198 views

Given a list of linear equations, what is a neat way to use solve on the equations of this list? [closed]

Suppose I have a list of equations, say {2x+b+3c=3, 7x+2b+c=1, x+b+9c=-2} what is a neat way to use Solve[] on that list? ...
0
votes
2answers
106 views

How to get F from this transcendental complex equation?

I want to solve this transcendental equation, but I don't know the step by step to get F in form equation and value of F ...
2
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0answers
73 views

Unable to solve for variables with subscripts [closed]

ΔF = 0.0025; Subscript[R, s] = Quantity[0.8, "SolarRadius"]; P = Quantity[8, "Days"]; When I solve for Rp ...
-1
votes
2answers
77 views

Non-linear equation

I have to solve this equation but the problem is X is function of x it means X[x] $$X(X-a)+ b e^{-2 X t}=B,$$ a,b,B are constants. How we can I get some result for ...
2
votes
1answer
47 views

Getting error Solve::units [closed]

I'm trying to solve the following formula for i, given values for all other variables. There are two equations, the first one is a formula to show the transit ...
0
votes
2answers
55 views

Plot Parametric f(x), inverse f(x) and f'(x) and then f(x)/f'(x) and inversef'(x)/inversef(x)

I want to plot f(x), inverse f(x) and f'(x) and then f(x)/f'(x) and inversef'(x)/inversef(x) f[x_] := 2 a ArcTanh[(# a)/Sqrt[-1 + #^2 b]] + a Log[1 + #^2 (a^2 - b)] - 2 Log[# b + Sqrt[-1 + #^2 b]] &...