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

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0answers
28 views

Solving a system of equations involving partial derivatives for a wave [on hold]

Before saying anything about the problem, I have checked "How to solve a system of partial differential equations?" yet it does not actually answers my question, as I have a 10x10 matrix to work on. ...
0
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1answer
42 views

Why does this work with Wolfram|Alpha but not Mathematica? [on hold]

I ran into this while doing some work today: It's the exact same syntax - and I expected that Mathematica would be more likely to be able to solve it, since oftentimes Wolfram|Alpha doesn't have ...
0
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0answers
30 views

Initial values/parameters in equation system of dimension 32

This is a system of equations of dimension 32, that describes an economic system. I want to find a set of parameters and initial values in which the system can be solved, and solve the system of ...
1
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1answer
41 views

Characterising the set of parameters that satisfy a system of non-linear equations

I am looking for a solution to the following problem and could not find an answer so far. I have a quintic equation, $f(x;a,b,c,\cdots)-x=0$, where $x$ is the variable with respect to which I need the ...
1
vote
1answer
175 views

solve recursion equation with condition

How can I find $f(x)$ in terms of $x$ in the following equation? $ -k\, x \,f(x) + k \, (x + 1)\, f(x + 1) - r \, f(x) + r\, f(x - 1) =0$ $r$ and $k$ are constants and $f(x)$ should satisfy: ...
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2answers
52 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
23 views

Solve and NSolve Parsing Error [on hold]

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: ...
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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 ...
2
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1answer
79 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: $$\frac{1+exp(b)}{1+exp(0.9a+b)}=0.95$$ $$\int_{0}^{\infty} \frac{1+exp(b)}{1+exp(a x+b)}=1$$
0
votes
1answer
57 views

In which condition releated to thee coefficients some equation has a solution

Please excuse me if the question seems to commonplace. Can Mathematica give a response to this question: In which condition related to the coefficients $c>0, \, n\geq 2, 0<p<1,\, a>c$ ...
0
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0answers
38 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
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1answer
70 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 ...
3
votes
3answers
889 views

Using DSolve to solve for x[t,parameter]

I'm trying to solve an ODE with two independent variables (a cannon firing from a cliff incorporating wind resistance dependent on velocity). I've tried the following for the x-component: ...
0
votes
1answer
447 views

Solve non linear system of equations

I am trying to solve a system of two equations with two unknowns. In these equations I have, a part from constants: Unknown nr 1, $$D_{\perp}$$ Unknown nr 2, $$\omega_C$$ Known function of r: ...
2
votes
0answers
48 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 ...
2
votes
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: ...
0
votes
1answer
58 views

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

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?
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2answers
91 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 ...
3
votes
1answer
117 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 ...
4
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2answers
121 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 ...
0
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0answers
42 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) ...
1
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1answer
81 views

RSolve works slow and does not give an analytical solution for solving high order linear difference equations

RSolve@@{{a[n]-a[n-10]==101}~Join~Table[a[i+1]==101+10i,{i,0,9}],a[n],n} I want to get the exact form of general formulas, but ...
0
votes
1answer
107 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 ...
0
votes
1answer
66 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
65 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 ...
1
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1answer
94 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 ...
3
votes
1answer
94 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 ...
3
votes
1answer
120 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 ...
4
votes
1answer
122 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 ...
1
vote
2answers
120 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
2answers
77 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
76 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
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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 ...
0
votes
2answers
195 views

Simplify trigonometric equation knowing that $\sin(a)=n \sin(b)$

I was working on a problem involving trigonometry. I used Mathematica to help me in solving it. I ended up with this formula: ...
-1
votes
1answer
88 views
2
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3answers
210 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. ...
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 ...
0
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1answer
80 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 ...
1
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0answers
35 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 $$u=y/x$$
3
votes
1answer
191 views

Using WhenEvent for derivative of discontinuous function

I have a discontinuous function ($u(t)$, a square wave) and I would like WhenEvent to trigger when the signal goes high/low, i.e. when the value of $u(t)$ changes. ...
-1
votes
0answers
59 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
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 ...
0
votes
1answer
252 views

Finding solutions of polynomials system

Let $f_1,...,f_n$ be a set of polynomials in $x_1,...,x_n$ with rational coefficients. I need to check whether a system $$f_1=a_1,...,f_n=a_n$$ has a real solution for large enough count of points. ...