# 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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3answers
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### 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 ...
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 <...
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 ...
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 ...
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 ...
4answers
145 views

### Solving radical equation

Intro I have encountered two radical expressions for which I have to find the roots analytically: ...
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 ...
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 ...
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 ...
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[]: ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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. ...
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 ...
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, ...
3answers
58 views

This code: ...
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 ...
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 ...
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? ...
3answers
499 views

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

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

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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 ...
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. ...
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 ...
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 ...
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 ...
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 ...
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 ...
0answers
53 views

### Solve method in Mathematica, symbolically solving method

I am looking for a way to solve this equation symbolically with Mathematica. ...
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 ][] This restricts ...
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: ...
0answers
44 views

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 ...
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]] &...