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

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0
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46 views

How to get x = 1.234 from {x -> 1.234}? [duplicate]

I'm a complete beginner in Mathematica (started a couple of days ago). I've solved a function using "Solve" and the result is this one: Out[1] = {x -> 0.000942939} How do I get the 0.000942939 ...
0
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0answers
46 views

Implement Lagrange Multiplier in NDSolve

I have a Lagrange function $L$ that depends on a couple of complex, time dependent coefficients $A_{\alpha,j,n}$ where $\alpha \in \lbrace{1,2\rbrace}$, $j,n \in \lbrace{1,\ldots,N\rbrace}$ where $N$ ...
0
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0answers
62 views

Solving numerically a system of equations using different methods

I will use, as an example, the simple Henon-Heiles potential ...
1
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2answers
85 views

Bessel-like equation problem with NDSolve

I am trying to solve the following nonlinear ODE, but Mathematica takes forever to give a result. Any idea why? ...
9
votes
2answers
183 views

NSolve finds real-valued results in version 9, but not in version 10

UPDATE Reals also was used in the code. Actually, I tried the following simple piece of code. ...
1
vote
1answer
58 views

how to replace one calaculation result to another one in a loop?

I am doing the calculation in a loop. I gain a digit for rzin in ...
1
vote
1answer
49 views

Approximating exponentials in a nice to read format

I need to make some approximations, basically I have something like $$ e^{i*a} = -0.735145 + 0.67791*I $$ and I want to approximate this to something that is easily readable, like $$ ...
0
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0answers
32 views

Combining two NDsolves results in “The search has encountered a complex value…” and no solution

So far I used to seperate NDsolves to solve a system of coupled differential equations, where the first NDsolve yields the Boundary conditions for the second NDsolve ...
4
votes
4answers
399 views

Solving complex equations with variable exponents

How would I go about solving $(1+i)^n = (1+\sqrt{3}i)^m$ for integer $m$ and $n$? I have tried ...
9
votes
1answer
175 views

Using Solve to solve the equation $x^{1/3}=-1$

I am curious why this command returned no answers: Solve[x^(1/3) == -1, x] Gives this output: (* {} *) I was able to get ...
3
votes
3answers
254 views

Number of solutions for inequality

Please explain me how can I calculate a number of possible solutions for such inequality and obtain those values: 3x + 7y + z <= 198 where ...
0
votes
0answers
58 views

Eliminating one function from non-linear PDE

Is there any solution to eliminate function p[x,y] from these two equations which are equal to zero (diff1=0 and diff2=0) where c and d are constants. I need one equation where should figure just ...
0
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1answer
61 views

What is the smallest number that equals the sum of two cubes in two ways? [closed]

How does one find the smallest number that equals the sum of two perfect cubes(positive) in two ways?
0
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0answers
33 views

Symbolic root computation of a function that depens on parameters

I'm given list of real numbers $a_i, i=1,N$, where usually $N \le 100$. Consider a function $f_N = f_N(x,a_1,...,a_n)$. I need to find the roots of $f_N(x)$ on $[-1,1]$, assuming that $a_i \notin ...
6
votes
0answers
125 views

Heat convection differential equations from 1952 - Mathematica “fails to converge”

I am trying to solve a fundamental problem in analytical convective heat transfer: laminar free convection flow and heat transfer from a flat plate parallel to the direction of the generating body ...
3
votes
1answer
138 views

How to speed up filling a matrix as much as possible in a loop?

In order to find the solution of an $n\times n$ system of nonlinear equations by the method $x_{k+1}=x_k-D_k^{-1}f(x_k)$ where $D_k$ is an approximation of the Jacobian and defined by ...
0
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1answer
49 views

DSolve - Complex Number Solutions

some of you know that I have been working on my dissertation of Game-Theoretic Modelling of Cybersecurity (Thank you again to everyone who has helped me with Mathematica so far). The differential ...
2
votes
1answer
63 views

Can't obtain Real results using NSolve

I am trying to find the critical properties of the Carnahan-Starling equation of state, $$p=\rho R T\frac{1+b\rho /4+(b\rho/4)^2-(b\rho/4)^3}{(1-b\rho /4)^3}-a\rho^2$$ using this system of equations, ...
2
votes
1answer
85 views

Product of $N\ 2 \times 2$ matrices and subsequently solving an equation dependent on the product

I have $N\ 2 \times 2$ matrices, each one containing one variable energy which may be complex. I want to muliply them all together to a single matrix ...
0
votes
1answer
56 views

Solve system of equations using a “singular” condition [closed]

I want to find a vector $x$ that is orthogonal to some vector $u$. The vector must satisfy the conditions $u\dot x = 0$ and $|x|^2=1$. Then I pass to Mathematica the next code: ...
1
vote
1answer
43 views

Finding root when using Apply command

I have normally two equations system which I reduce to one equation and make its graphic. I could make the graph of the reduced equation but I can not find the appropriate command to find its root. ...
0
votes
1answer
99 views

Solve this equation explicitly for $\beta$

Solve this equation explicitly for $\beta$: $$T_{12}=\frac{x_{11}+x_{22}}{1+|\beta|^2}\beta$$ $x_{11}$ and $x_{22}$ are positive real numbers where $x_{11}>x_{22}$ and $T_{12}$ and $\beta$ are ...
-1
votes
3answers
58 views

Calculate an expression given constraints [closed]

How can I solve the following problem using Mathematica? If $a+b+c=0$ and $a^2 + b^2 +c^2 = 0$, calculate $a\,b+b\,c+c\,a$.
0
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0answers
49 views

DSolve DAE echoing - no solution/response

I am aware that there are lots of questions about this topic but they are all slightly different. I am attempting to program a cybersecurity infection model and there are 4 states that a computer can ...
3
votes
1answer
66 views

SolveAlways 'never' completes

After allowing Mathematica to run on ...
2
votes
1answer
60 views

Mathematica's Solve[] and LinearSolve[] doesn't work to solve a system of equations IF parameters are not replaced

(I'm working on Mathematica 10.3) I have a system of 81 algebraic linear equations with 81 variables (variables are a1 to a81). ...
5
votes
1answer
163 views

$x^6-2\varphi^5x^5+2\varphi x+\varphi^6=0$ solving in radicals

How to solve the equation $x^6-2\varphi^5x^5+2\varphi x+\varphi^6=0$ in radicals using Mathematica? where $\varphi$ is the golden ratio. Solution is Ramanujan's Class Invariant $G_{125}$, Class ...
3
votes
1answer
94 views

Proof or find counterexample to inequality (in three vars)

I'm trying to show \begin{eqnarray*} \left(\frac{1-q^r}{1-q^n}\right)^{\frac{1}{n-r}} \left(\frac{q^n \log (q)}{\left(1-q^n\right) (n-r)}-\frac{\log ...
2
votes
1answer
77 views

Inputs which make two function have the same value [closed]

Suppose I have two function f(x1,...,xN) and g(x1,...,xN). How can I find the values ...
0
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0answers
80 views

solving an equation containing an complex integral

I want to solve a numerical equation which include an integral. The problem parameters are : w (is a complex : w = wr +I wi), ...
0
votes
0answers
98 views

Given $y$, find the $x$ value of a point on a Bezier curve

I have linear equation of Bezier curve with one control point: f[x_] := (1 – t)^2 x0 + 2 (1 – t) t x1 + t^2 x2; f[y_] := (1 – t)^2 y0 + 2 (1 – t) t y1 + t^2 y2; ...
4
votes
0answers
98 views

VERY slow to solve a nonlinear equation involving matrix eigenvalues

I am trying to solve a problem similar to the following: ...
-1
votes
1answer
64 views

Parametric solving a nonlinear equation and plotting answer

I want to get x and y as a function of z in below nonlinear equations and plot ...
3
votes
1answer
110 views

plotting a function on a (x,y) plane

I looked at different questions asked concerning the error message that I get but it did not help. I try to plot a function. Here is the code that I use ; ...
6
votes
3answers
244 views

Labeling solutions of an Eigenvalue equation involving Bessel functions

I'm solving the Schrödinger equation for a particle in an annular geometry with hard wall boundary conditions and I've reduced it to the following equation: $$J_m(k\,R_1)\,Y_m(k\,R_2) - ...
1
vote
0answers
79 views

Truncate an infinite continued fraction at order 2000

I want to solve an equation which contains an infinite continued fraction F(n). Then I must (obviously) truncate this continued fraction at n=2000. The problem here is tha Mathematica does not ...
0
votes
0answers
65 views

Solving system of Fredholm integral equations of the second kind

How can we generalize the code previously introduced to solve the Fredholm equation of the second kind to the case of a system of Fredholm integral equations of the second kind? $$ ...
3
votes
6answers
288 views

Avoiding a For-loop when finding the solution to a set of polynomial equations

There are several examples and questions regarding Map, but I couldn't find what I need. This is a minimal working example. I have two functions $\qquad ...
3
votes
4answers
503 views

NSolve didn't get the answer for my equations within 24 hours

I have two polynomials as function of $wa$ and $wb$ , I am going to show those polynomials. This is the expression for $GS65$: ...
1
vote
1answer
60 views

Solving a system of non-linear equations?

I want to solve the following system of equations: ...
0
votes
0answers
65 views

Finding double inverse Laplace transform numerically

Edit: I asked Prof. Valko, he was so nice to point out where the mistake is. The problem is solved ! Thank you for your attention ! Recall the the double Laplace transform of a function $f(x,t)$ is ...
3
votes
1answer
87 views

Dsolve and Differential Equation for botnet defence

I am currently using Mathematica to solve $\frac{\mathrm{d}x(t) }{\mathrm{d} t} = cv_{H} (1-x) + \beta x(1-x) - (\gamma_{min} - v_{D}(\gamma_{max} - \gamma_{min}))x$ with $ x(0) = 0$. In the ...
8
votes
3answers
353 views

Bug: Wrong results from NSolve on coupled polynomials. WorkingPrecision->Automatic fails

OP UPDATE: I received an email from WR on 1-18-2016: "...It does appear that the NSolve function is not behaving properly in this case and I have forwarded an incident report to our developers with ...
3
votes
1answer
100 views

How to solve coupled multi-variable polynomials?

The following code generates two polynomials $q_1$ and $q_2$ in complex variables p and c: ...
3
votes
1answer
84 views

Solving a list of equation which takes so much time

I try to solve a list of equation in a following way but it Mathematica solves equations after 30-40 minutes or don't solve them at all. The functions that I use are ; ...
1
vote
2answers
118 views

steady state conditions

I want to find the steady state value of variables in NDSolve but the variables have oscillation. Do you help me? ...
3
votes
4answers
78 views

Constructing a matrix of solutions using findroot

I would like to solve the following equation numerically: Sinh[y]-(y+Tanh[x])Cosh[y]-y Sech[x]^2==0 I would like to do it by creating a list of x values: ...
0
votes
1answer
45 views

Solve equations and express with specific varible

I have two equations as below: eq1: $8 \pi \gamma r-\frac{4 \pi \text{Delta$\_\mu $} r^2}{\text{v$\_$c}}=0$ eq2: $\text{Delta$\_\mu $}=\text{K$\_$b} S T$ When I try ...
1
vote
1answer
59 views