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3
votes
1answer
2k views

Solve a function with sum in Mathematica?

I want to solve an equation with sum in Mathematica, e.g., $$\sum _i \frac{a_i}{x}=1$$ But when I input this: Solve[Sum[Subscript[a, i]/x, i] == 1, x] ...
1
vote
1answer
413 views

Possible bug in Mathematica?

I'm running Mathematica 7.0.0 and came across this weird calculation (lines 1-14). ...
1
vote
2answers
153 views

Taking advantage of linearity of integration in Mathematica

I want to evaluate an integral of form given below $$\int\limits_\alpha^\beta (f(x) + g(x) + h(x) + ...) dx$$ When I give it to Mathematica it takes forever to evaluate. But if I give it in this ...
0
votes
2answers
252 views

How to solve this equation in Mathematica

How do I solve this equation in Mathematica? Using the NSolve command doesn't work! ...
-1
votes
1answer
238 views

How to make Runge-Kutta for solving nonlinear ODE system in Mathematica

How to make Runge Kutta method for system of non linear equations in this Matrix form. Matrices A3, B3 and B4 are functions of matrix X3. Initial conditions are X1=X2=X3=X4=0 and system is here $$ ...
0
votes
1answer
70 views

A function of two functions that loses dependence on an argument

Say I have two functions: f[a_,b_]:=a + b g[c_,d_,e_]:=c + d - e And I define a third function: ...
0
votes
2answers
115 views

Create list of {x,f(x)} pairs

How can I do this in Mathematica: r=Range[0,20,0.13]; fr = HeavisideTheta[r]; data = somecoolfunctionsinmathematica[r,fr] So that data now is in the form useful ...
1
vote
1answer
161 views

Plotting a Function

How can one plot a three-dimensional plot of a differential equation system of the following to show the trajectories in mathematica: $x' = yz,~ y' = -2xz,~ z' = xy$ I tried using ...
0
votes
0answers
63 views

Using Fit on functions that use matrix calculation

I am struggling with using Fit to fit a (linear combination of a) list of functions, that are calculated using matrices. It seems Mathematica internally uses ...
2
votes
0answers
344 views

Calculate periodicity in 1-dimensional array with noise

I have a 1-dimensional array with some integers, which are periodically increasing. Something like this (1 period here): ...
0
votes
1answer
347 views

How to obtain integral in Mathematica faster? (Using parallel table?)

Hello Wolfram killers, Sasha was near, but how to obtain these two integrals? Ok 500 is to much for calculating, but 200, ok? ...
0
votes
1answer
225 views

How to obtain big matrix in Mathematica?

Can you help me how to obtain big but simple matrix in Mathematica? ...
2
votes
4answers
166 views

Simplify an expression to show equivalence

I am trying to simplify the following expression I have encountered in a book $\sum_{k=0}^{K-1}\left(\begin{array}{c} K\\ k+1 \end{array}\right)x^{k+1}(1-x)^{K-1-k}$ and according to the book, it ...
2
votes
2answers
290 views

What is the “Mathematica” function for plotting a single variable inequality?

I was just wondering, how do I plot a single variable inequality in Mathematica? For example, we could use Wolfram Alpha for plotting an inequality like $x^3+4x+9 > 0$ and see something like this. ...
0
votes
1answer
156 views

Help needed with something like Matlab Solver or Mathematica Solver

I have never learnt to use the services (I have them though) but now I was given a massive amount of equations and I cannot really handle them without some solver tool, just plug equations and ...
0
votes
1answer
536 views

Mathematica - How to solve for the equilibrium?

So, I used Mathematica to create a basic SIR Disease model using the following equations: ...
0
votes
1answer
674 views

Eigenvalues problem in Mathematica

The simple problem eigenvalues problem defined as: $A-(x^2)*B = 0$, where $A$ and $B$ are matrices. How to use command Eigenvalues[] in Mathematica to find $x$, ...
3
votes
2answers
1k views

Function as parameter in Wolfram Mathematica

I want to define some basic functions known from "discrete analysis": $$I(f)(x):=f(x)$$ $$E(f)(x):=f(x+1)$$ $$\Delta(f)(x) := (E-I)(f)(x) = f(x+1)-f(x)$$ $$\nabla(f)(x) := (I-E^{-1})(f)(x) = ...
0
votes
1answer
1k views

Mathematica: Specifying assumptions/domains doesn't seem to work?

I frequently have trouble trying to place limits on Solve or Reduce using assumptions and domains. For example, this code: ...
0
votes
2answers
190 views

Solving ODE in Mathematica

I want to solve an ODE in the form $\{y'[t] == f[y[t]], y[2] == \{1, 2, 3\}\}$ using NDSolve in Mathematica, where $f: R^3 \rightarrow R^3$ is defined as follows, ...
0
votes
2answers
3k views

How to draw an parabolic path between two points

I have two sets of points and i want draw an parabolic arc between two points and also to find the intermediate points which the parabolic path is drawn.... In the above image you can see the curve ...
-1
votes
1answer
612 views

NDSolve simple matrix problem in mathematica

I have a problem with command NDSolve in mathematica. If we have simple second order differential equation, it is easy to write code in mathematica. But if we have matrix problem (for example 4 ...
1
vote
0answers
409 views

How to make iteration for Newmark method in Mathematica 8

How to make iteration method for solving differential equations by Newmark method? There are just three equations which describe the Newmark method. I need q for time step for example 0.01. Also, for ...
1
vote
2answers
445 views

Mathematica 8 can not solve Eigenvalue problem

I cannot explain this eigenvalue problem. Both matrices are positive definite and symmetric, but some solutions are complex. But if it is matrices lower order, solutions are real. As I increase the ...
4
votes
1answer
232 views

Why does (Full)Simplify return terms with $0^n$ coefficients?

When I use Simplify[] or FullSimplify[], specifying domain reals, I get terms with $0^n$ as the coefficient. Isn't that always ...
1
vote
3answers
311 views

Simple problem with pattern matching in Mathematica

I'm having trouble setting a pattern for simplifying a complex expression. I've distilled the question down to the simplest case where Mathematica seems to fail. I set up a simple rule based on a ...
3
votes
1answer
127 views

The limit of the expectation of the top half+1 order stats of $n$ draws of $X$ as $n\to\infty$?

Can anyone help me compute the limit of the average of the top half +1 of order marginal order distribution of $n$ draws from $X$, as $i\to\infty$? Specifically, the limit as $i\to\infty$ of ...
0
votes
2answers
204 views

How do I transform an array into the Traditional Form with mathematica?

I am trying to set an expression in Mathematica that uses an array. However it is problematic to typeset this expression and still be able to use it. Here is my example: ...
4
votes
2answers
332 views

Independent High School Research

StackExchange Gurus! I'll keep this question short and to the point. I'm going into my senior year of high school, will have an independent research period, and have few ides of what to do during ...
0
votes
2answers
245 views

Plot graph with custom axes

How to plot graph with custom axes in Mathematica 8.0? e.g. use the axes $\frac1y$ instead of $y$ and $x^2$ instead of $x$? this is to implement Linear Law
0
votes
1answer
188 views

Equation to find if a set of vertices form a concave shape?

i'm trying to get around the rule of only being able to form concave shapes in the SFML c++ library by forming the non-concave shape out of many concave shapes. What I don't know is the equation for ...
0
votes
1answer
118 views

Poles placement problem

It is an equations of inverted pendulum. Example of controlling him with pole placement. $$ \text{eqns}=(M+m)x\text{''}[t]-m l \text{Sin}[\theta [t]] \theta '[t]^2+m l \text{Cos}[\theta ...
1
vote
0answers
182 views

Euler method on differential equation problem

I have this problem to solve. I want to compute the inclination of a plane $\theta(t)$ at every frame of a simulation given the following rule for its angular speed of rotation $\omega(t)$ $$ ...
2
votes
2answers
143 views

Computation of characteristic polynomial fails for me

For a matrix $A\in\mathbb{K}^{n\times n}$ where $\mathbb{K}\in\{\mathbb{R},\mathbb{C}\}$ the characteristic polynomial is defined as $$\chi_A(\lambda) := \text{det}(A-\lambda I_n) = \sum_{k=0}^n c_k ...
2
votes
2answers
315 views

help with old Mathematica file

I am trying to solve a problem, for what I finally found a book what has some Mathematica files supplied, but I am stuck now as I cannot run the files. My problem is that I cannot run the program as ...
2
votes
2answers
293 views

Closed-form Expression for $\sum_{j=0}^{k-1}(2j+2)\sum_{i=1}^j \frac 1 {i^2}$? (problem with Mathematica)

I need to calculate a closed-form expression for $\sum_{j=0}^{k-1}(2j+2)\sum_{i=1}^j \frac 1 {i^2}$. This isn't particularly difficult, and I do it by hand pretty much routinely. However I found out ...
2
votes
2answers
267 views

Branch points of an equation

I was reading the Mathematica Guidebook to Symbolics by Michael Trott, and saw the following expression to evaluate the branch points of a Riemann surface given by $f(x,a)=x^3+x^2+ax-1/2$. ...
0
votes
4answers
3k views

How to tell Mathematica about a constant?

Sometimes I want to ask mathematica to plot or calculate something without given a certain value for it .. For example I may want to ask mathematica to integrate $\int{a x} \mathrm{d}x$! How to tell ...
1
vote
1answer
356 views

Trying to pick a random point on sphere end up picking from a lune

I was inspired by this question to play around a little bit (its a weekend). I was pretty confident of my derivation and thought it might be nice to supplement it with a pretty picture. However, ...
0
votes
2answers
216 views

Mathematica Equation Solving

Suppose I wanted to solve the following for $a[1], a[2], a[3]$ in the Mathematica code: (a[1]+a[3])*t+(a[1]+2*a[2])*t^2=0 with $a[1] = 1$ where $t$ is just a ...
1
vote
0answers
508 views

Mathematica: How to convert scales to frequencies?

According to the transform $$w(u,s)=\frac{1}{\sqrt{s}}\int _{-\infty }^{\infty }x(t) \psi ^*\left(\frac{t-u}{s}\right)dt,$$ the frequency should be $f=\omega/(2\pi)=1/(2\pi s)$ (is it right?), where ...
1
vote
2answers
386 views

How to find endpoint?

How do you find the coordinates of endpoint of arc (pi + s) when the endpoint of arc s on the unit circle is (-sqrt (21)/5, 2/5)?
1
vote
1answer
216 views

Mathematica VectorPlot with Piecewise arguments

Why won't this output the VectorPlot? It outputs number (that even seems correct for the application), but I can't get a picture out of them :( ...
1
vote
2answers
153 views

Informal Equivalents of Mathematica “Set” and “SetDelayed”

How would one distinguish between what is meant by Mathematica's "Set" and "SetDelayed" functions in informal mathematical notation? Is there a way to make this distinction any any reasonably standard ...
4
votes
2answers
503 views

Integrate in Mathematica takes forever

I'm trying to calculate the length of a curve from a polynomial in Mathematica and for some reason Integrate doesn't complete, it just runs until I abort the execution. The polynom: ...
2
votes
1answer
249 views

Mathematica fails with boolean simplification with exponents

I have a truly simple inequality, which I want to prove using Mathematica: $$ a^x \geq 1 ,\quad \quad with \quad 1\leq a \quad and \quad 1\leq x \quad a,x \in R$$ This is obviously true. When I try ...
3
votes
2answers
867 views

Compute unknown limit from known integral in Mathematica?

I have an integral $\int_a^b \! f(x) \, \mathrm{d}x = c$ where I know c and either a or b. Now I want to compute either b or a (i.e., the missing limit). How would I do that in Mathematica/Wolfram ...
3
votes
2answers
522 views

Union on Graph Data in Mathematica

I have begun working with Mathematica for some Graph Theory, and I want to compute the number of spanning trees of all cubic graphs up to 12 vertices. I have found that GraphData["Cubic", 12] will ...
7
votes
3answers
1k views

Local variables when defining function in Mathematica

I defined a function in Mathematica. It is a function of n, so f[n_]:=, but in the definition, I used a sum, $\sum_{k=0}^n$. So, the $k$ is just an index variable for the sum and no $k$ shows up in ...
2
votes
1answer
320 views

Working with Conditions or Assumptions in Mathematica with boolean operators

I have the following code: $Assumptions = {x > 0} b[x_] := x^2 b'[x] > 0 In my (very basic) understanding of Mathematica, this should give me me the Output ...