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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2answers
33 views

Evaluate with numbers from list

This code works: x=2 y/.Solve[y==x^2] Out[138]= 2 Out[139]= {4} So above I put number in variable x and getting the result of ...
2
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2answers
122 views

Underdetermined system of equations

Could anyone help me solve this probably simple equation? ...
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0answers
28 views

Ploting output of Solve[] and Expand[] that returns two results on one plot with Plot[] [closed]

I have code: Expand[Solve[x^2 + y^2 == 25, y]] output is: For this code: y /. Expand[Solve[x^2 + y^2 == 25, y]] output is: ...
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4answers
116 views

Is it possible to get a symbolic or numeric relation when solving a transcendental equation? [closed]

Here is the code. Solve[(1 - E^x + (3 x^2)/2)/(2 x) == a, x, Reals] Unfortunately, Mathematica told me that this system cannot be solved with the methods ...
2
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2answers
83 views

How can I solve $\coth (2 x )=x $? [duplicate]

I have this equation $$\coth (2 x )=x $$ and I want to solve it to find $x$. The methods Solve and Reduce do not work. Coth[2 x] == x
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0answers
56 views

what does that mean?? How to fix it? [closed]

Hey I need help to fix this problem please I am looking to solve form factor of scattering ...
2
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1answer
93 views

How to solve system of PDE's with complicated initial and boundary conditions

I am trying to solve the Cavity problem given in Paper by Mansour et al. with a physical model . System of PDE and B.C are . How can I impose boundary conditions like this? Code ...
1
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1answer
34 views

Find the condition under which an inequality holds

I've got an inequality of 8 non-negative parameters (arising from a 5x5 matrix) and would like to find a condition under which my inequality holds. The condition would be an inequality too of these ...
0
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0answers
31 views

How to deal with unknown variables in NSolve?

I am trying to solve these equations by using NSolve and want to plot $p1^{2}+p2^{2}$ v/s P0. But there is some problem, it is showing running... but not showing any error. I don't know where I am ...
1
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1answer
68 views

Why mathematica does not solve the equation $x\left \lfloor x \right \rfloor=10$ for $x$?

The equation $x\left \lfloor x \right \rfloor=10$ has a real solution, which is $x=\frac{10}{3}$. But when I type Solve[x*Floor[x] == 10, x] a message comes: "...
6
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3answers
138 views

Verify an inequality of many parameters

I've got an inequality of 10 non-negative parameters (arising from a 5x5 matrix) and would like to verify whether it holds. I tried the following, which doesn't seem to work: ...
0
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1answer
38 views

how to solve a quadratic diophanic equation on integers and obtain various results

This quadratic di equation has more results, as it came to them. I can only think of this FindInstance[(4 p + 3 q - 2) (p - 1) == (6 p + 2 q) q, {p, q}, Integers] ...
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0answers
52 views

Using Reduce with a Interpolation function

I am trying to find all the solutions of an equation that contains an interpolation function int, where int=Interpolation[data] (...
3
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1answer
86 views

fixed rate mortgage

I am trying to make sense of how mortgage repayment figures are calculated for two tier mortgages, where you fix your interest rate for a certain period and after that period, you fall back to the SVR ...
4
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1answer
126 views

Simplifying the final coefficient expression of the solution to a Laplacian

I have been trying to solve a boundary value problem analytically which involves a three-dimensional temperature Laplacian over a parallelepiped. In the final step of my solution, using the two non-...
0
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1answer
27 views

why mathematica Holds the Solve on the set of equations in the diagonal a matrix?

Say I have a simple function F[x_, y_, z_, r_, a_, b_, c_, d_] := (1 - a + b - (b/3) (c x + d (y + z + r))) x And I want to solve the set of equations given by: <...
2
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1answer
50 views

Find non-unique Hermitian solution to pair of matrix equations

This is a continuation of my previous question here, but I previously did not fully specify some of the restrictions on the matrices and so the solutions posted there were not that helpful. I'm ...
2
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1answer
52 views

How to get the result from a RootSum?

While working on an integral, I got this scary-looking expression. I tried to use // Normal // ToRadicals // FullSimplify to get the answer, but it is taking lot of ...
17
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5answers
2k views

periodic boundary conditions and NDEigensystem

Mathematica 10 has a splendid new function, NDEigensystem, that makes it possible to solve Sturm-Liouville problems numerically in a single step. I have not however been able to find a way to get it ...
0
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1answer
128 views

Make Arrows Smaller

I have the following program that describes a 3D curve in space with an osculating circle and TNB vectors moving with the curve. The arrows indicating the TNB vectors are way too large making it seem ...
1
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1answer
30 views

Get Solution range of NSolve

I have a numerical solution and when I solve it with NSolve, and substitue the results in an expression, I get something like: 1 + x + x^2 if 0 < x< 10 I ...
3
votes
1answer
73 views

Solving Inequalities using Mathematica

How can I solve this inequality using Mathematica? Sqrt[B^2 + J^2] Cosh[(2 J)/T ] < J Sinh[ (2 Sqrt[B^2 + J^2])/T] where T, J, and B are reals and they are >...
1
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3answers
63 views

How to solve these complex equations for plot?

I am trying to Plot this code but it is not showing any plot. I want a bistable type plot between "NL" and "P0" and there are six equations and six unknowns. The code is given ...
0
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1answer
51 views

Problem of Encountered non-numerical value for a derivative at t == 0

I try to solve this equation numerically : eq= z''[t] + (2691+ D[Log[Abs[z'[t]^2]],t]) (z'[t]^2 + Abs[z'[t]]^2 ) == 0; By ...
2
votes
1answer
77 views

Converting an equation to the form $ax+by=c$

I have a linear equation that comes as a result of applying orthogonality on a non-homogeneous boundary condition with two unknowns $C_1$ and $C_2$. Can someone help me to express this equation in the ...
1
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1answer
103 views

Solving symbolic system of non-linear equations takes too long

I am trying to solve a set of system of symbolic non-linear equations: ...
0
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1answer
83 views

correct use of the command FindInstance

I have tried to solve this system for numbers that go from 1 to 10 non-repeated integers, this occurs to me ...
6
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2answers
449 views

Numerical solution to a nonlinear Ordinary Differential Equation

I am trying to solve the following ODE for $f(x)$: $$x f' - f = \frac{(f')^2}{\gamma^2}[1-({f}')^\gamma]^2$$ where $\gamma < 0$ and real, which makes the ODE highly nonlinear. Since I am not ...
3
votes
1answer
90 views

Problem with NDSolveValue : “The function value {$Failed} is not a list of numbers with \ dimensions…”

I was having fun modifying a code given to me as an answer to a previous problem here, courtesy of user Alex Trounev (Thank you again), when I encountered a certain error which I had never seen before....
3
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2answers
159 views

Solving the Shifted Neutral Axis Problem

Problem Description: In solving the "Shifted Neutral Axis" method for the stress distribution of a vertical steel vessel supported on a concrete foundation, we can derive the following ...
0
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1answer
40 views

How to solve all the solutions of this restricted system of equations?

The system of equations is as follows: ...
3
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2answers
187 views

Maxima turn out to be false maxima when extremising function locally

In short: I have a 2-D function that gives this plot, where the orange dots are maxima: There are 4 maxima in this plot. Now, I plot the function again in a smaller region, close to these maxima, ...
16
votes
7answers
548 views

Missing solution - system of equations

Attention! This example already works as expected in Wolfram Mathematica 12.1.1.0 for function Solve. The problem was in version 12.1.0.0. Check out answer of Bob ...
3
votes
1answer
65 views

Solve an equation with real parameters

I am trying to solve $$ \left(\eta ^2-1\right) \cosh ^2(\beta \eta )+2 J^2=2 \eta (J \sinh (\beta \eta ) \sinh (\beta J)+\eta \cosh (\beta \eta ) \cosh (\beta J)) $$ for $\eta$. Where, $\beta, ...
2
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1answer
58 views

How to chop complex number from solution solve using a model

Hi I have a set of 4 solution that was solved using a 4th order polynomial equation. I have noticed that some of the real number solution occurred through the list of 4 set of solutions. I have ...
5
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2answers
913 views

Using RSolve correctly

I am having problems persuading Mathematica to solve even the simplest recurrence relations. As an example, how would you do the following? ...
1
vote
1answer
51 views

Solve won't find solution to simultaneous matrix equations

I'm trying to solve a pair of simultaneous matrix equations of the form, $$AX + XA^\dagger + BJB^\dagger = 0,\ \ X C^\dagger + B J D^\dagger = 0,$$ where, $$J = \begin{bmatrix}1&0\\0&-1\end{...
4
votes
1answer
56 views

Solve a linear sytem of differential equations (Cauchy problem)

I'm trying to solve a linear Cauchy problem (which should have a unique solution) as: $\dot{X}=Q^{11}X+Q^{12}Y,X(0)=I$ $\dot{Y}=Q^{21}X+Q^{22}Y,Y(0)=0$ The matrices $Q^{11}, Q^{12}, Q^{21}, Q^{22}$ ...
0
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1answer
29 views

How to plot a Root[] object? [closed]

I got a solution in the form of a Root object from an equation: ...
6
votes
4answers
132 views

Solve system of ODEs for steady state symbolically

I can successfully solve a linear system of ODEs describing chemical reactions by first using DSolveValue to find the general solution and then taking the limit to infinity to find the steady state ...
3
votes
3answers
98 views

Find solution for specific similarity transformation

I have a situation where I need to find a similarity transformation of a specific form. I have some Hermitian matrix $X$, and I need to find a matrix $T$ that satisfies $X = T J T^\dagger$ where, $$ J ...
1
vote
1answer
76 views

Problem solving a function using FindRoot and then plotting it

When I run the following code: ...
0
votes
2answers
647 views

Plotting the solution of a Chini differential equation

In DIFFERENTIAL EQUATION SOLVING WITH DSOLVE by D. Kapadia, there is a Chini differential equation : sol = DSolve[x'[t] == 5 x[t]^4 + 3 x[t]^(-4/3), x[t], t] ...
1
vote
1answer
61 views

How to solve complex equations and plot the graph?

I am trying to solve these equations and want to plot the value of $a^{\dagger}a$ versus P0. I have tried this code but this gives me an error like "Conjunction::argr: Conjunction called with 1 ...
1
vote
1answer
41 views

How to solve integral of second-degree exponential function?

I am trying to solve the internal of the second-degree exponential function. But Solve fails to give the solution. Is there any way to get the solution? By the way, I don't understand the ability ...
4
votes
2answers
110 views

Re-writing $f(x, y)$ as $g(x)h(y)$ [duplicate]

Is there a general way of re-writing a function of two variables as a product of two functions, $$f(x, y) = g(x)h(y)$$ Specifically, I’m trying to write an expression, $$f(x, y) = \frac{a y - x}{y - 1}...
2
votes
1answer
90 views

Solving a system of polynomial equations - can I be sure that the number of solutions, and the solutions are correct?

I need to solve a system of two polynomials with integer coefficients in two variables, $\{Q_1(w,z)=0,\,Q_2(w,z)=0\}$, and want to compute all real solutions. I'm able to run ...
3
votes
1answer
98 views

Solve 2D Difference Equations

If I have a system of difference equations $$ \begin{cases} x(n + 1) = x(n) + x(n) y(n) + y(n)^2 \\ y(n + 1) = y(n) - x(n)^2 + y(n)^2 \end{cases}, \text{ with } \begin{cases} x(0) = 1\\ y(0) = 2 \end{...
1
vote
1answer
51 views

Real Roots of Cubic equation [duplicate]

If I have the cubic equation, how can i find the real root of x ? I try this but i get complex root Solve[b (q - 1)*(x^3) + (m - s)*(x^2) + (a - n)*x + v == 0, x] ...
4
votes
3answers
72 views

Solving an equation for a space dependent variable

How can I find $f(x)$ in the interval $(x_1,x_2)$? I know the values of the coefficients as $c=0.5$, $b=1.1$ and $(x_1,x_2)=(-10,10)$. f[x] == c Cos[2 f[x]] + b x ...

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