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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0answers
14 views

Very slow solve and problem when solving in a nested for loop

I am using a nested for loop to solve a system of equation for {a, ga} for 2 varying parameters: here it's rm and sig. ...
0
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0answers
16 views

Solve and NSolve Parsing Error

I've been using Mathematica to do simple line intersection solutions, particularly using NSolve. However, I've been running into the following bug recently. When trying to solve for the following: ...
2
votes
2answers
54 views
0
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0answers
50 views

Enormous and unclear output when using Solve

After running for about 30 minutes the program yields the below-given unclear output (of course I didn't copy the whole output, only a small part of it). So it explicitely gives 3 possible solutions ...
0
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0answers
37 views

Selecting values over lists for discrete inputs in NDSolve

I'm currently trying to simulate a step response in a simple tank system with NDSolve. I would like it to start at say time 2 (the precise time is not important). ...
0
votes
1answer
69 views

Solving a complicated system

Could anybody please make a suggestion how can I implement this program which attempts to solve $2$ dimensional complex system of equations? My computer is not able to solve... After 3 hours the ...
2
votes
1answer
77 views

How to obtain numerical answer for equation containing integration

Could some one tell me how to obtain numerical value of $a$ and $b$ from equations below: $$\frac{1+exp(b)}{1+exp(0.9a+b)}=0.95$$ $$\int_{0}^{\infty} \frac{1+exp(b)}{1+exp(a x+b)}=1$$
2
votes
0answers
43 views

NDSolve is running an extremely long time: how can I save the existing data?

I am trying to solve a PDE by the following code. It takes 1 hour or so to reach t=25.72 but about 20 hours to reach t=25.72404031638060174049337306126853310997. Actually, the time step is extremely ...
0
votes
1answer
56 views

how to solve line and ellipse equations in 3D? [on hold]

I have a point and a vector to find the line equation, and ellipse equation in 3D. I need to solve the two equations of line and ellipse in 3D. how can I do this, what equations should I use?
2
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0answers
104 views

Proving large inequality in 6 variables

I have arrived at a very large inequality in 6 variables that I would like to prove is true. The command I have tried is the following: ...
4
votes
2answers
119 views

How can I get all solutions of a system of equations with Reduce?

The post What is the difference between Reduce and Solve? discusses the difference between Reduce and Solve. Now, with the ...
3
votes
1answer
109 views

Fick's Law over Implicit Regions

I'm trying to solve 2D Fick's law of diffusion from the boundaries of a triangle (future shapes will include more complex implicit regions). I'm able to model diffusion without time in complex ...
0
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0answers
37 views

Using Jacobi Method [closed]

I am solving matrix with Jacobi method on Mathematica 5.2 Got problem, It needs to be 40 iterations, Initial approximation is x1=0, x2=0, x3=0 Please help to fix it. In[14]:= !(* RowBox[{( (Q5) ...
0
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0answers
40 views

Why NMinimize doesn't work [closed]

I have some problem with my code. I need to find root for functional equation F(x)=0, where function F is complex subroutine that uses some external programs for calculation and after all routines ...
0
votes
1answer
65 views

Weird behavior when solving a simple physics problem

I have the following code in Mathematica that represents two balls being thrown, one with a velocity v10 (6 in this case) and another ball thrown with a velocity v20 (its just dropped) one second ...
0
votes
2answers
64 views

How to exract the roots from “Roots”? [duplicate]

Given how the output looks like, as in a set of "==" assignments, is it possible to extract specific roots from the output of, http://reference.wolfram.com/language/ref/Roots.html ? And then do a ...
0
votes
1answer
105 views

How do I write nested for-loops?

Looking through the reference.wolfram, I couldn't see an example of how to write a multiple line "for" loop in Mathematica. I need to nest many for-loops in such a way I can do many things in the ...
1
vote
0answers
42 views
0
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0answers
58 views

A confusion about comparing WolframAlpha results with Sage [closed]

The following is a characteristic polynomial of a 4 dimensional Hermitian matrix and hence I expect 4 real roots! So I have the equation, $f(x) = (x^2 - 6)x^2 - 4x(e^{(2/5)i\pi} + e^{-(2/5)i\pi}) ...
3
votes
1answer
118 views

Solving Non-linear System of Equations

I need to get a symbolic solution to a system of non-linear equations (equation 8 is non-linear), but Mathematica is running for ever and gives no answer. Is there another way to get the solution? My ...
3
votes
1answer
93 views

How to reduce a quartic form to a quadratic form with equal roots

Preface: To clear the theoretical background this question is cross-posted on math.stackexchange here. I have a polynomial in $n$ variables of the form ...
1
vote
1answer
92 views

Runge-Kutta Butcher tables

I like to have the Butcher's table for Explicit (or implicit as well) Runge-Kutta method of a fixed order. I do not understand reading ...
4
votes
1answer
121 views

Solving 2-D Mechanical Systems

I'm trying to use Mathematica to solve a particular 2-d mechanical system. The system comes from "DESIGN AND OPTIMIZATION OF AN EIGHT-BAR LEGGED WALKING MECHANISM IMITATING A KINETIC SCULPTURE, “WIND ...
0
votes
2answers
76 views

Solving a system of two equations

I have a system of two equations with the variables T and X that I tried to solve: ...
-3
votes
1answer
75 views

How to make X and Y = Z? [closed]

Hello I have a big question, maybe it's extremely easy but for now I'm unable to make it work. I'm a programmer and what I need to do is for example: if X = 2 and Y = 1 then Z = 1 if X = 3 and Y = 1 ...
0
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0answers
51 views

Computation doesn't Finish

I'm trying to solve some problem by the following code: ...
0
votes
0answers
46 views

Finding an instance of parameters, for which a polynomial has no zeros

I have a polynomial in $p(x,y) \in\mathbb{R}[x,y]_{\leq 4}$, of degree 4. The coefficients are simple functions of 12 real parameters. In particular, the coefficients are in ...
-1
votes
1answer
88 views

Find $r$,in terms of variables $U$ and $V$

I want to solve this equation, for $r$: ...
0
votes
1answer
60 views

How to solve Mod equation with mathematica [closed]

i'm pretty noob with mathematica but i need to solve an equation: $$c\equiv m^2\pmod n$$ I tried something like ...
1
vote
0answers
34 views

Input `Reduce[Mod[a + x, l] == 0, x]' and output `x == -a + kl`?

Reduce[a + x == k l && k > 0, x] (* k > 0 && x == -a + k l *) I think a + x == k l and ...
0
votes
1answer
50 views

How can I solve a difference-differential equation with new variable? [closed]

I want to ask how we can solve this equation: $$ xyy' = x^2+2y^2 $$ I tried with new variable $$u=y/x$$
-1
votes
0answers
58 views

Solve a system of equations with double subscripts

I am trying to solve the following system of four equations for $P_{i,j}[s]$: $$\left(\lambda _0+s\right) P_{0,j}(s)=\mu _1 P_{1,j}(s)+P_{0,j}(0) ; ~where ~j=0,1,...,L$$ $$\left(\theta +\lambda ...
0
votes
0answers
28 views
0
votes
1answer
79 views

solve equations with high degree

this is my code,i want to solve this equations.can anyone give me some help about this,wheather mathematica can solve this.thanks a lot ...
0
votes
1answer
50 views

If domain Reals specified all constants should be real? Problem with Solve

I've got a problem solving an equation. I want to solve: Solve[Arg[h]==0, r0, Reals] with h being some imaginary number ...
1
vote
2answers
106 views

Problems with Solve when constraining solutions to a range

I have the following code ...
1
vote
2answers
119 views

Intersection with FindInstance

How to find individual root parameters pair ( t, T) to find curve intersections using FindInstance? Hopefully it would output two, instead of 6 pairs in the following: ...
0
votes
0answers
65 views

Trying to Simplify an Expression

I'm trying to simplify an expression: ...
0
votes
2answers
50 views

Solving coefficients of a function having boundary conditions

I have a function F=c+dz, which has particular boundary values, say F(z=1)=2 and F(z=-1)=1, ...
2
votes
3answers
208 views

Points of Intersection

How to numerically find points of intersection between pair of curves (Here,a circle and a parabola) ? Finding it a bit messy as, for a point on one curve, slope of the other is involved. ...
2
votes
1answer
96 views

Symbolic quadratic constrained maximization with non-negativity constraints?

Dear Mathematica users, I attempted to maximize the below quadratic function K, subject to x1+x2<=A, and a series of ...
-2
votes
2answers
143 views
10
votes
8answers
423 views

Find the minimum integer r such that $(10^r - 1)/37$ is an integer

I know Element[(10^r - 1)/37, Integers] tests the condition. So what is the command that gives me the minimum integer value r ...
0
votes
2answers
90 views

Obtaining the relations of variables using diagonal matrices

I know this is too an elementary question, but I am a pathetic newbie in mathematica and I cannot find any answer by googling. What I want is obtaining some relations of unknown variables using their ...
0
votes
1answer
65 views

Solve with limit over multiple variables

Very new to Mathematica so apologies for what is probably numpty question. The following returns no solutions. However, there is a solution! If I set a = 1 I get the solution b = 1/2. Can you explain ...
0
votes
0answers
61 views

solving singular matrix [duplicate]

Hello I have a matrix that is singular, and i wanted to use linear solve to solve it but that doesn't work with mathematica. The matrix given as a list looks like this: ...
4
votes
2answers
128 views

Specifying and solving a PDE on an L-shaped domain

I wish to solve Laplace's equation with Dirchlet boundary conditions on an L-shaped domain as described here http://www.inf.ethz.ch/personal/tulink/FEM14/Ch1_ElmanSyvesterWathen_Ox05.pdf I know how ...
6
votes
4answers
132 views

Minimizing a function with a constant $l > 0$

I'm VERY new to Mathematica and would like some help with minimizing a function. $$f(x) = \frac{1}{2} \sqrt{\frac{\left(l^4+x^4\right)^2}{l^4 x^2}}$$ I want to find which $x-value$ (probably ...
0
votes
0answers
35 views

Plotting the real positive solution to a parametric equation [duplicate]

I have the following parametric equation $$ x^2-a=0 $$ where $a$ is a given parameter. I would like to plot the nonnegative real root ($\sqrt{a}$) using NSolve as $a$ varies from $0$ to $1$. Can ...