Questions tagged [equation-solving]
Questions on the analytic and numerical equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).
5,384
questions
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
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?
...
-2
votes
0answers
28 views
newtons method using newton method examine the convergence as a function of complex starting [closed]
[![enter image description here]
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
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
44 views
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 ...
