Questions tagged [equation-solving]
Questions on the analytic and numerical equation solving functions of Mathematica (Solve, Reduce, NSolve, FindRoot, DSolve, RSolve, etc.).
3,874
questions
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Non-Numerical Error Solving ODE [on hold]
In using NDSolve, I return the error:
*'NDSolve:Encountered non-numerical value for a derivative at t == 0.'*
Though I believe I've set every non-numerical ...
1
vote
1answer
85 views
How to solve PDE with periodic and anti-periodic b.c.?
I need to solve the PDE for a complex function $A(x,t)=A_r(x,t)+iA_i(x,t)$
...
2
votes
0answers
38 views
Speed up NDSolve for an integro-differential equation
On the MMA.SE, there have been several user cases on how to solve integro-differential equations using NDSolve, see example 1, example 2, and example 3. Many people,...
2
votes
1answer
134 views
Solve is not working with this equation
I was trying to solve this equation and Mathematica 12 keeps trying but does not give an answer.
Is it a glitch in my system or something wrong with Mathematica 12?
...
1
vote
1answer
90 views
NSolve gives weird result for $n=101$ with NSolve[$\frac{d}{dx}\prod \limits_{k=1}^n (x-k)$==0,x]
Coming from this post: What would be the roots of the derivate of this polynom I did a quick check with Mathematica and arrived at a wrong result. I was initially confused but chose to trust ...
0
votes
1answer
34 views
Evaluation functions with lower and upper limit ODE?
How do I find the numerical value of y at 0 and also at 1. Here is my code. I appreciate any help.
...
3
votes
1answer
148 views
Simple Solve[{y == 5 + 2 x + x^a}, {x}] not working?
I am trying to find a general expression for x, for the following equation y = 5 + 2 x + x^a, but Solve cannot accomplish this.
...
0
votes
1answer
143 views
How to solve this differential equation analytically?
How can I DSolve the following differential equation?
Is there an analytical answer to this equation?
...
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0answers
33 views
How to find closed form expression for a particular variable?
Is it possible to get a closed-form expression for variable W in the expression given in the figure using mathematica. Please guide me as I have been stuck in this problem for quite some time.
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0answers
56 views
Reduce, Solve, RSolve for symbolic equations? Neither seems to work for my problem
I want to solve the followiwng system of equations:
Through substitution I get:
I want to solve this equation for P_t
I tried the following:
...
6
votes
1answer
116 views
How to solve this 1st-order linear ODE system with a few discrete eigenvalues?
I am trying to solve the eigensystem of a 1st-order linear ODE system in the region $(-\infty,\infty)$ and with Dirichlet boundary condition at the infinities
$$
-i\partial_xu(x)+f^*(x)v(x)=\lambda u(...
0
votes
1answer
49 views
Having trouble with Solve [closed]
I am unable to solve the following system of equations using Solve.
...
5
votes
2answers
110 views
How to find the shape parameters of of a beta distribution given the position of two quantiles?
How to find the shape parameters of of a beta distribution given the position of two quantiles?
I am trying to find $\alpha$ and $\beta$ the shape parameters of a beta distribution.
I know that my ...
1
vote
0answers
77 views
Can I use Mathematica to derive these induction equations? [closed]
I have the following model
T + 1 dates, t = 0, 1, ...,T
This was all solved by hand and I wanted to ask if Mathematica can be used to do the job instead?
If so, what commands are helpful?
0
votes
0answers
39 views
how to solve for unknowns by comparing coefficients? [closed]
When we solve equations, sometimes we just compare the coefficient of each term. For example, if we want the identity $Ax^2+Bx+C=2x^2-x+3$ to satisfy for all $x$, then the solutions are $A=2,B=-1,C=3$....
1
vote
1answer
69 views
FindRoot Accuracy
How can I get FindRoot to be more accurate? I would require a solution for r that leaves ...
1
vote
1answer
49 views
Determine inverse function with Gröbner basis
I am trying to generalize a way to invert a function using Gröbner basis. My functions are defined in the following form:
...
0
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0answers
34 views
Why do all the Roots not show up in ContourPlot of an equation?
Roots by Normal Method:
f[x_] := (Sin[x] + Cos[x] - Sqrt[2]) Sqrt[-11 x - x^2 - 30];
Reduce[(Sin[x] + Cos[x] - Sqrt[2]) Sqrt[-11 x - x^2 - 30] == 0, x]
Which ...
1
vote
2answers
74 views
How can I get solutions of this trigonometric equation?
I am trying to solve the equation
$$\left(\sin (x)+\cos (x)-\sqrt{2}\right)\cdot \sqrt{-11 x-x^2-30}=0$$ in Real domain. I tried
First way
...
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0answers
66 views
1
vote
1answer
64 views
Trying to solve analytically (or at least numerically) a set of equations
I have a set of two equations regarding equations of state of some stars. I have a lot of variables that depend upon each other (all the μ's). I also have a parameter, ρ. Ideally I'd like to get the ...
1
vote
0answers
42 views
One of the roots obtained by Reduce for a complex polynomial is wrong [closed]
I am trying to find the roots of a complex polynomial using Reduce but one of these roots is wrong. Here is the code:
...
1
vote
1answer
59 views
For loop for two variable at the same time
Can I use for loop for two variables as example show below at the same time?
for (int x = 0, y = 0; x < 10 && y < 10; x++, y++)
2
votes
1answer
34 views
Solving for Tan[x] = y/z in the range of $x = 0$ and $\pi/2$
I feel this should be simple
Reduce[Tan[x] == y/z && 0 < x && x < \[Pi]/2 && y > 0 &&
z > 0, x, Reals]
should ...
0
votes
2answers
48 views
Solution to non-algebraic equation with parameters
I have to solve the following equation a Tanh[z-b] = z, with a and b parameters and ...
0
votes
2answers
104 views
Solving complicated implicit function
I consider the following function:
bound[K10_] := xi - (p0*(Q10 - K10)/(p0 - K10 + Sqrt[(K10)^2 - m1^2]*(1 - 2*alpha)))/(u0Max);
This function is basically an ...
0
votes
2answers
43 views
How to solve a complex equation
I am trying to solve a complex equation for 'z' in terms of 'f'. At the moment my Mathematica is stuck running...
Just wondering if anyone has any ideas, I know 0 < z < 40 if that helps.
<...
1
vote
2answers
87 views
Can someone help me to solve this equation? [closed]
Solve[beta*
phi *((1 + (1 - m)*alpha*theta ((phi^(-0.5) - 1)/((1 - theta)*phi^(-0.5) + theta)))) -
delta == 0, phi]
I run it and get nothing showing as results. ...
0
votes
0answers
39 views
Trigonometric derivation using Solve
Background: I'm trying to derive the relation between two variables in an optical system. The derivation is simple and well-known in the limiting case ($H \to \infty$, see figure), but rather tricky ...
0
votes
1answer
47 views
How to solve this equation by Solve?
I have an equation to be solved. But Mathematica does not work for it. I hope the solution x can be expressed as a function of a and b
...
0
votes
2answers
51 views
Problem with Solve in harmonic oscillator
Why is the result not Indeterminate?
Solve[x == a Cos[ω t + ϕ] /. {x -> 0, t -> 0, ϕ -> π/2}, a]
when the result ...
3
votes
2answers
128 views
Solving Equations with HeavisideTheta Functions
I need to solve an equation that involves the HeavisideTheta[] function, but regardless of the method I use Mathematica returns an error message. For example,
<...
5
votes
1answer
133 views
Runtime too long for NDSolveValue, FindRoot breaks down at sharp turns
I have two equations:
$$
\frac{2}{3}\thinspace\left(\frac{\varepsilon}{\Delta}\right)^{\frac{3}{2}}=\sum_{i=1,2} \sigma_i\lambda_{i}\left(1+\lambda_{i}^{2}\right)^{\frac{1}{4}}E\left(\frac{\pi}{2},k_{...
4
votes
2answers
112 views
Reduce is not working for my equation
Can anybody help me?
Reduce[{Cos[Sqrt[w]]*Cosh[Sqrt[w]]*L == 1, w > 0}, w]
This procedure takes a long time and is not working. Can anybody help me?
1
vote
2answers
75 views
Zeros of high degree polynomials
I am working with Hermite polynomials in Mathematica with the built-in function HermiteH. I want to compute the zeros of the polynomial ...
0
votes
0answers
28 views
List of answer to solve with interdependant solutions
I am solving a fairly annoying matrix equation order by order in perturbation around a small parameter. I am solving for a list of free parameter that are $\beta 1[1],\beta 0[1],\alpha 0[1], \beta m1[...
0
votes
0answers
43 views
Solving a system of linear equations with complex unknown
I am trying to solve the system of equations which is given by $ABA^*=-B$, where A is $2\times2$ matrix, $A^*$ is a conjugate transpose of $A$ and $B$ is a $2 \times 2$ unitary matrix. Entries of both ...
1
vote
1answer
79 views
How to use the roots of equations? [closed]
Can anyone explain to me how can I use the roots of an equation? Let clarify my question with one example. Suppose that I have an equation which I want to find its root:
...
0
votes
0answers
70 views
How to differentiate a function constructed through FindRoot?
I am trying to maximize a function which has as a variable another function that was solved numerically using FindRoot. My code is below.I start by defining some parameters
...
1
vote
1answer
59 views
How do I use Solve with conditional equations?
Short version: How do I have Solve handle a system of equations where some of the equations may be conditional?
Simplified Problem:
I am solving the following system of equations:
a * b = 10^-14
b^...
0
votes
1answer
49 views
Power::infy: Infinite expression 1/0. encountered
I am trying to solve the following linear system consisting of four unknowns.
...
0
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0answers
51 views
InterpolatingFunction in NSolve
I'm trying to get NSolve to solve a simple system of equations. It makes use of various interpolating functions (for thermodynamic properties). I can solve the system outside of NSolve by ordering the ...
1
vote
1answer
52 views
Interpreting the solution for a nonlinear system in a matrix form
I have an issue of how to interpret the solution of the following nonlinear system in a matrix:
$F=PX^{-1}AX+wL$
where $w>0$ is a scalar, $F=(F_1,F_2)$, $P=(P_1,P_2)$, and $L=(L_1,L_2)$ are all a ...
4
votes
3answers
119 views
How to find maximum/minimum in `ContourPlot`?
The ContourPlot of Sin[x^3 + y] - 2 Cos[x y]==0 has a maximum around (-1.8,-2.3), see figure ...
2
votes
0answers
126 views
Finding the radius of a circle given that it is tangent to both axes and contains (10, 9) [migrated]
A circle is tangent to both axes in the 1st quadrant of the xy-plane. If the point (10, 9) is on the circle, what is the circle radius?
0
votes
1answer
59 views
Is it possible to use FindRoot with a function of two variables? [closed]
How can I use FindRoot with 2 variables function? Is there a different way to do that?
For example
...
0
votes
1answer
35 views
Conditions to make unitary a given matrix
Suppose I have some symmetric matrix W = {{c[1, 1], c[1, 2], c[1, 3]}, {c[1, 2], c[2, 2],c[2, 3]}, {c[1, 3], c[2, 3], c[3, 3]}}; where the c's are complex and I ...
3
votes
1answer
41 views
Finding closed forms for various addition laws on elliptic curves, FullSimplify fails even with assumptions?
I would like to get Mathematica to do some tedious algebra for me, but I have been unsuccessful so far, and I don't know whether I am not using it correctly or whether it is simply not sophisticated ...
1
vote
1answer
135 views
How do you solve a Lyapunov equation with given parameters? [closed]
The following matrix equation is a Lyapunov equation,
$$ mA.x+ x.mA^T=-mC,$$
the matrix $mA$ is given by
$$
mA= \begin{pmatrix}
\frac {\gamma}{2} & \omega_{m} & 0 & 0\...
