Questions tagged [equation-solving]

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

Filter by
Sorted by
Tagged with
0
votes
0answers
26 views

Figure out original balance with only the amount of loss and amount of decrease [closed]

I'm sure there is an easy solution to this, but I can't remember how to set something like this up. I was thinking a differential equation may be the answer. For context, this relates to stocks, but ...
-1
votes
1answer
28 views

Simplifying an equation in which all the terms are integrals with respect to the same variable

I have an equation in the following form: Integrate[A[x], x] + Integrate[B[x], x] == Integrate[C[x],x] How can I simplify this equation to get: ...
3
votes
1answer
111 views

Stability analysis of coupled ODE's

I'd like to reproduce Panel A of Figure 7 (red curve) of this paper, which represents the steady-state solutions of four coupled ODE's, and verify this claim that the diagonal branch in the Z-shape ...
0
votes
0answers
54 views

FindRoot doesn't find root

I am facing a problem that my FindRoot doesn't find the actual roots. I am trying to make a loop that iterates my parameter sets (U0,X0,\Sigma0) to find sets that satisfy some conditions. Here is my ...
3
votes
2answers
81 views

What are some techniques used to speed up numerical solving (with NSolve)?

I have a rather complicated set of equation to solve, as shown in the code below: ...
0
votes
1answer
77 views

Solving a system of coupled trigonometric equations to find angles

I have a system of 9 coupled trigonometric equations (a 3X3 Matrix). I am trying to find four unknown angles $\theta_1, \theta_2, \phi_1, \phi_2$ by solving any 4 out of 9 such equations. $\text{M}=\...
0
votes
1answer
66 views

DSolve and Plot [closed]

I was working on this equation to solve and plot it, but I'm little bit confuse?! ...
2
votes
1answer
71 views

How to use NDsolve for 2D PDE?

I want to solve the following 2D-PDE using NDsolve and plot it, I did: ...
1
vote
1answer
79 views

FindRoot of matrix operation equations

I have a question in FindRoot of matrix operation equations. It's my first time use Matrix operation in FindRoot, i have write a ...
1
vote
0answers
122 views

How to numerically solve this system?

Our system: \begin{align} \dot S &= \mu -\beta_1 S I_2 -\beta_2 S J-\beta_3 S A - \nu S\\[2ex] \dot {I_1} &= p \beta_1 S I_1 +q \beta_2 S J +r \beta_3 S A + \xi_1 J- b_1 I_1 \\[2ex] \dot{...
0
votes
1answer
100 views

Solving a system of differential-algebraic equations

I am trying to solve a coupled system of differential-algebraic equations as follows. First define a list of 6 equations ...
3
votes
3answers
227 views

Solving for a unique set of solutions

I have the following code: ...
2
votes
1answer
159 views

How can I solve Hypergeometric function?

I have tried several ways to solve this equation (Hypergeometric) by Solve and FindRoot, and it still does not work. ...
2
votes
1answer
150 views

how can I solve this logarithmic equation?

I've tried NSolve, Solve and Reduce for solving this equation but non of them worked. would you please help me? ...
3
votes
1answer
44 views

Eliminating "contained" solution subsets for Solve[]

Here are the first two lines of a Solve[] that went through in a few seconds (yay, Mathematica, I more expected three days due to the system being highly nonlinear ...
2
votes
2answers
150 views

Numerical solution of the 2D-spatial nonlinear Allen equation

I would like to solve the 2D-spatial Allen equation in rectangular coordinate, which is a nonlinear reaction-diffusion PDE of the type $$\partial_{t}u=\epsilon(\partial_{xx}+\partial_{yy})u + u - u^{3}...
1
vote
0answers
24 views

N on equation with numbered variables [duplicate]

Say I have a system of polynomial equations in the variables x[1],...,x[n]. Sometimes want to make such equations numerical (as in: the coefficients become floats) ...
1
vote
3answers
139 views

Plotting the solutions of the equation $e^{-z}=z$ in the complex plane

I would like to plot in the complex plane the solutions of the equation $$e^{-z}=z.$$ I tried this: I took $z=a+ib$ and took the real and imaginary part of the equation: ...
-2
votes
1answer
60 views

How to use NDsolve for PDE? [closed]

I am trying to use NDsolve to solve PDE which has an exact solution and evaluate the absolute error: ...
1
vote
1answer
42 views

No real solution for 3 coupled equations, but then how "close" can one get?

I have three equations involving $x$, $y$, and $z$ that I would like to find a unique solution to, in the Reals. NSolve does not find anything: ...
0
votes
1answer
54 views

NSolve syntax for region

I am trying to solve these simultaneous system of equations only in a specified rectangle going from -100<x<100 and -100<y<100. But I think I am making a syntax error and hence I m not ...
0
votes
0answers
27 views

Passing Erfc function through Reduce?

I have the following function. ...
2
votes
2answers
57 views

Sum three equations [closed]

I would like to compute x1+x2-x3 based on three equations as defined in equations variable. See below: ...
2
votes
2answers
120 views

Any way to get Mathematica to Solve[Sin[Tan[x]]-Tan[Sin[x]]==0,x]?

Solve[Sin[Tan[x]] - Tan[Sin[x]] == 0, x] It says it runs out of methods. After a very long time. Plotting the expression shows there are periodic solutions and ...
-1
votes
1answer
94 views

A No-linear differential equation

I'm recently figuring out how to make this equation solved but Mathematica does not solve this??!! DSolve[{ y'[t]== ((3 a)/2 (y[t] - b/(2 a))^2 + k ((3 a)/2 - 1) t^-2 - ((a f)/2 + (3 b^2)/(8 a)))/(t ...
0
votes
2answers
40 views

FindRoot with vector function

I have trouble with FindRoot for vector variables, I have search MMA SE find a solution. in Szabolcs‘s code, Vector FindRoot ...
2
votes
2answers
86 views

How to realize NDSolve by NSolve with the implicit constraint equations?

Daniel post the amazing code to realize numerical integrators, I think it is useful to the kind of one-step explicit equation like x[k+1]-x[k]== constant_number. In ...
0
votes
1answer
54 views

How to realize NDSolve by Solve?

I want realize the NDSolve by Solve,so I read some numerical integration resource. In common setting, ODEs can be solve by Euler ...
0
votes
0answers
33 views

Converting 1D map into first order differential equation for bifurcation diagram code

I have existing code to plot bifurcation diagram for coupled first order differential equations. It seems to work for coupled differential equations. To test the code further, I use the simplest ...
4
votes
3answers
163 views

How to use Findroot in a loop

Consider: i = 0.1; While[ i < 0.9, y[x_] := y /. FindRoot[{u/(1 - u) (x + Log[y]) - 1 /. u -> i}, {y, 3}]; Plot[y[x], {x, 0, 4}]; i = i + 0.1] I want ...
1
vote
0answers
42 views

How to fix a parameter in SolveAlways

In expression: SolveAlways[f1(a)+f2(b)x+f3(c)x^2+f4(d)x^3==f5(d)x^2+f6(e),x] Functions fi are known. How do I tell mathematica that d is a fixed constant?. I want ...
2
votes
2answers
144 views

FindMinimum::lstol

I have a function SQ[b,zQ,zh] where I want to find at which zQ it is a minimum given b and <...
2
votes
1answer
135 views

Why reduce does not give solution for ArcTan[Tan[x]] == x?

Basic question I can't see why now. This works Simplify[ArcTan[Tan[x]] == x, Assumptions -> -Pi/2 < x < Pi/2] (*True*) But ...
1
vote
0answers
50 views

Solving a 1D diffusion equation [duplicate]

I am new to Mathematica and I'm trying to find the analytical solution to the diffusion of excess pore pressure in a porous media using this equation: $$ \frac{\partial P}{\partial t} - \alpha \nabla^...
0
votes
3answers
46 views

NSolve not giving a solution

I have a parameter set paramFinal2 = {\[Beta] -> 0.2, \[Alpha] -> 0.5 , c -> 0.150, b -> 0.1, \[Kappa] -> 1}; I define the following variable ...
0
votes
0answers
47 views

Inverse VS Reduce

I got a solution I want to get inverse but it is not working in Mathematica or Rubi: ...
0
votes
1answer
46 views

"Instantiate" an output of Solve [closed]

I would like to use Mathematica to find a non-trivial solution of the linear system $Ax = 0$. When I try running Solve[A.x == 0, x] the output I receive is a ...
0
votes
1answer
37 views

Want a DiscretePlot of an NSolve that uses a parameter n

Let's say I want to solve f[n,R]==0 with respect to R for n=1,2,3,... (up to some upper ...
0
votes
0answers
32 views

please help me resolve find what method gives me a result for this

I have this mathematic problem: (124164a/300b/2360/.85)+(124164a/25b/2360/.85)+(124164a/55b/2360/.85)=3.81=(a/b/2360/.85) And this is the result: a≈87.4514, b≈0.0114422 I payed for WolframAlpha Pro ...
0
votes
1answer
43 views

Findroot to evaluated a function that become multivalued and varying of a parameter

I am having problem in solving this equation: s[t_?NumericQ, l_?NumericQ] :=FindRoot[s - Sin[t - (l*s)] == 0, {s, t, l}, Method -> "Automatic"][[1, 2]] ...
2
votes
0answers
94 views

Why does this ConditionalExpression appear? [closed]

I am new to Mathematica. Could anyone help explain why ws > 0 appears in the solution? How to define symbolic variables' range? Thanks! EDIT to include code <...
0
votes
0answers
63 views

FindMinimum/FindRoot failed to converge

I have a function SQ where it is also determined by sig. For b=0.1 and ...
2
votes
1answer
60 views

Strange behavior of NDSolve (Error NDSolve::ntdvdae)

i discovered a weird behavior using ```NDSolve``` to solve a set of differential equations. Let me outline my problem: I need to solve a set of differential equations. These are equations of motion ...
2
votes
2answers
294 views

How can I find the only real and then the smallest root of a 4th-order polynomial?

I just want to solve the below polynomial for real roots only, where I have mentioned the conditions on all variables, a,d,m,L. ...
2
votes
0answers
52 views

I need help with a basic Solve question

I have the following two conditions: Dc == t0^2 Dp == t1^2 The actual formulas I'm trying to solve are more complex, but this is the essence of the relations. I ...
0
votes
2answers
52 views

How to use NSolve while specifying the range of one variable

I have an equation that uses three variables that I have defined as follows: b[l_, m_, lt_] := 0.025 * (((1 - m)*l)^(-1/2))*((1 - m)*lt) - 5. After this definition, ...
0
votes
0answers
35 views

Different Outputs from Solve

These commands tell me that y=x^2 doesn't intersect the x-axis. But when I enter this slightly differently the intersection points appear. What's happening? This code tells me that y=x^2 doesn't ...
1
vote
1answer
55 views

LogicalExpand does not work correct?

I have a boolean expression and need to distribute all it's part. I used LogicalExpand and it works fine somehow. but I see for some sub-parts it does not Simpify or solve it. I tried Simplify for ...

1
2 3 4 5
108