Markiyan Hirnyk

Markiyan Hirnyk
10 years, 191 days


These are questions asked by Markiyan Hirnyk

I accidentally came across a nice Mma animation. Unfortunately, I am able to present only few frames of it in MaplePrimes. See two inconsecutive frames below

 

I find this animation very deep. I don't remember something similar. It looks like an iterative
map shown in its dynamics. Not being an expert in Mathematica, I don't understand the machinery of the generating code.
n = 1000;
r := RandomInteger[{1, n}];
f := (#/(.01 + Sqrt[#.#])) & /@ (x[[#]] - x) &;
s := With[{r1 = r}, p[[r1]] = r; q[[r1]] = r];
x = RandomReal[{-1, 1}, {n, 2}];
{p, q} = RandomInteger[{1, n}, {2, n}];
Graphics[{PointSize[0.007], Dynamic[If[r < 100, s];
Point[x = 0.995 x + 0.02 f[p] - 0.01 f[q]]]}, PlotRange -> 2]
Here is its fragment translated into Maple:
>with(MmaTranslator):
>FromMma(" (#/(.01 + Sqrt[#.#])) & /@ (x[[#]] - x) &;");
map(unapply(_Z1/(0.1e-1+sqrt(_Z1 . _Z1)), _Z1), unapply(x(_Z1)-x, _Z1))
To my regret,
>FromMma(" n = 1000;
r := RandomInteger[{1, n}];
f := (#/(.01 + Sqrt[#.#])) & /@ (x[[#]] - x) &;
s := With[{r1 = r}, p[[r1]] = r; q[[r1]] = r];
x = RandomReal[{-1, 1}, {n, 2}];
{p, q} = RandomInteger[{1, n}, {2, n}];
Graphics[{PointSize[0.007], Dynamic[If[r < 100, s];
Point[x = 0.995 x + 0.02 f[p] - 0.01 f[q]]]}, PlotRange -> 2]");
Error, (in MmaTranslator:-FromMma) incorrect syntax (at position 11) in last character of "...0)
r"

This week I am participating in 19th Ising lectures (see https://drive.google.com/folderview?id=0B0uPwoK-03XgSEZpYWljYnpXN0U&usp=sharing). The Serguei Nechaev's talk inspired me to ask the question:
"How to simulate a random walk on an undirected and unweighted (and, of course, connected) graph
(All the paths from a vertex of degree k have the same probability 1/k.)?"
A Maple procedure to this end is welcome.

of a (concrete/general) triangle, making use of Maple tools in an efficient way?  Mathematica applies the barycentric coordinates and the Dirichlet distribution to this end. More generally, how to efficiently choose a random point in a given bounded region?

Let us consider the maximum value of the polynomial

x^4+c*x^2+x^3+d*x-c-1

on the interval x=-1..1 as a function g of the parameters c and d. General considerations suggest its continuity. However, a plot3d of g does not  confirm it.  Also the question arises "Is the function g(c,d) bounded from below?". Here is my try with the DirectSearch and NLPSolve:

 

restart;
``

g(10, -10)

9.

(1)

plot(x^4+x^3+10*x^2-10*x-10-1, x = -1 .. 1)

 

plot3d(g, -5 .. 5, -5 .. 5, grid = [100, 100], style = surface, color = "DarkOliveGreen")

 

DirectSearch:-GlobalOptima(proc (a, b) options operator, arrow; g(a, b) end proc, {a = -1000 .. 1000, b = -1000 .. 1000}, variables = [a, b])

[-167.208333252089, Vector(2, {(1) = 999.9999999975528, (2) = 166.20833325208952}, datatype = float[8]), 815]

(2)

DirectSearch:-GlobalOptima( (a, b) -> g(a, b), variables = [a, b])

DirectSearch:-GlobalOptima(proc (a, b) options operator, arrow; g(a, b) end proc, variables = [a, b])

Error, (in Optimization:-NLPSolve) invalid input: PolynomialTools:-CoefficientVector expects its 1st argument, poly, to be of type polynom(anything, x), but received HFloat(HFloat(undefined))*x^4+HFloat(HFloat(undefined))*x^3+HFloat(HFloat(undefined))*x^2+HFloat(HFloat(undefined))*x+HFloat(HFloat(undefined))

 

``

 

Download bound.mw

 

I mean

J := int((x^2+2*x+1+(3*x+1)*sqrt(x+ln(x)))/(x*sqrt(x+ln(x))*(x+sqrt(x+ln(x)))), x);

Of course, with Maple.

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