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

learn more… | top users | synonyms (5)

0
votes
0answers
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
votes
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 $N$ ...
1
vote
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
180 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. ...
4
votes
4answers
397 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 ...
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 ...
0
votes
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 ...
8
votes
3answers
350 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 ...
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 $$ ...
9
votes
1answer
173 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 ...
4
votes
2answers
160 views

Find condition under which variables fall away

I have a somewhat lengthy expression, looking like expr = 1 + x + b + Pi + 2*a Is there some way of generating a relationship between ...
3
votes
3answers
252 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
57 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
votes
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
votes
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 ...
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 ...
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 ...
0
votes
1answer
48 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
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 ...
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, ...
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. ...
3
votes
1answer
162 views

How to change parameters to equations of physical properties they belong to in an equation?

First off, I want to apologize for my poor English as I am not a native speaker. In my physics research, I had to solve a system of equations, from which I would get a solution for the speed of an ...
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
vote
1answer
134 views

Why does Mathematica not restrict the domains of Rational Expressions?

As taught in High School Mathematics: $$\begin{array}{ccl} \left\{ {(x-3)(x+3)\over 5(x+3)} : \ x\ne -3 \right\} & \ne & \left\{ {x-3\over 5} : \ x\in\mathbb{R} \right\} \\ \left\{ ...
2
votes
1answer
240 views

Structure analysis based on direct stiffness method. Solve taking too much time

The program generates a very large matrix based on some input from the user. The matrix is symmetric and called generalstifnessmatrix. It also generates 2 other lists(displacement and forces list) ...
-1
votes
3answers
57 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
votes
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
2
votes
1answer
59 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
76 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
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; ...
0
votes
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), ...
4
votes
0answers
95 views
-1
votes
1answer
63 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
6answers
287 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
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 ; ...
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
64 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
2answers
251 views

How to propel the integration of time a little bit further? Numerical solution can not evolve to the max time

I try to solve a nonlinear partial differential equation. I obtain a numerical solution which can not continue to the max time I set, I always receive message NDSolve::ndcf: Repeated convergence ...
1
vote
1answer
99 views

Wrong root when using numerical values

I have the following inequality: $$ \sqrt{\frac{a}{2x}}+ \frac{b}{1-\frac{a}{a+\sqrt{a(2bx + a)}}} + \frac{a}{2x\frac{a}{a+\sqrt{a(2bx + a)}}\left(1-\frac{a}{a+\sqrt{a(2bx + a)}}\right)} < f $$ on ...
3
votes
2answers
728 views

Methods for NSolve

I've been using NSolve a moderate (50-100 equations) size system of linear equations and it has been working splendidly (Solve ...
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
59 views

Solving a system of non-linear equations?

I want to solve the following system of equations: ...
1
vote
0answers
169 views

Help with calculating a complicated integral

Edit: The question is solved : )) Thank you for your attention ! I am sorry for mass questions, but the question bothers me a lot. So I would like to ask this question here. This problem arises when ...
0
votes
0answers
64 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 ...