## Plot in 3D over triangle...

Is there an elegant way to plot the region between the surfaces z=-y^2 and z=x^2, only on the domain of the XY-plane bounded by the triangle with vertices (0,0), (1,0) and (1,1)?

## How to simulate random walks on graphs?...

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.

## Section of a 3d spherical plot function...

Is there an elegant way to plot in 3d only the portion of the function f(x,y)=sqrt(25-x^2-y^2) for which 9 <= x^2+y^2 <= 16 ? I'm looking for a nice plot that shows it against the whole sphere with radius 5, so that it's clear which part of the sphere is cut out.

## Problem with subsection insertion...

I have a Document that I have been putting together.  When I insert a Subsection into a section below the title I get a 1D-math input command symbol.  Is there a way to prevent this from happening?  I have not had this problem before.

It appears there is something confused in the startup of the document because when I start a new document and this doesn't happen.

It's almost like when I insert the subsection it converts that part to a worksheet?????

## Fill a distribution plot...

with(Statistics):
X := RandomVariable(Normal(0, 1))

DensityPlot(X,filled=true)

I don't know why the plot doesn't produce a shaded plot.

## Solving nonlinear recurrence equation...

How to solve following recurrence equation:

a(0)=2;

a(n+1)=a(n)+a(n)^2

I tried,but it doesn't work.

How to find the sequence an ?

Maple_worsheet.mw

Mariusz Iwaniuk

## Where is "lib" folder in Maple on OS X?...

Maple tech support sent me a third party application for my Maple 2016 to solve a problem that I'm working on. I was instructed to copy and paste a few items from the download: "to your "<maple>/lib" folder" Unfortunately I cannot access "lib" in my Maple "Applications" folder on my OS X MacBook Pro.

This is what Maple Tech Support sent me:

"Another option you may want to look into is the "DirectSearch" package (which is third-party, and not supported by us), which would need to be downloaded from the Maplesoft Application Centre:

There is a function "GlobalOptima()", which allows one to search for a global minimum to the objective function, as opposed to a local minimum like commands such as "LSSolve()". To install, you can extract the files "DirectSearch.mla", "DirectSearch.help", and "DirectSearch.hdb" to your "<maple>/lib" folder."

Any suggestions?

## Creating of symmetric n-rank tensor ...

I need to create n-order tensor filled with any symbolic variable, for exemple 'x', but "symbol" option works only on vectors and matrix, so i don't know how to do that on n-order array.

X := Vector(3, symbol = x);#------ Work
Matrix(3, 3, symbol = x);#------ Work

Array(1 .. 3, 1 .. 3, 1 .. 3, symbol = x);
Error, argument `symbol = x` is incorrect or out of order

And 2nd problem thet globaly i need to create symmetric n-order tensor with symmitry for any pair of index and with contraction for any couple of indexes equal to zero. As i understend i need to create a big list of equations for every individual pair of index and 2 conditions (contraction and symmitry) and solve it to get a match and combination of independent index and paste values in them?

## How to filter DataFrame with strings?...

How do I filter a DataFrame using a value in a string column?
I have a CSV file containing records. Some columns are numbers, others are strings.
The examples in the tutorials are good for filtering on numbers but I can't see how to filter using a string.

ie I have 1300 records with ID, Name, Region, enrolments, ...
enrolments is a number and I can filter on that.
Region is a column of strings. I want to filter on that and work with all records from a specific region.

Thanks,
David Moss

## How to read a JSON file?...

Dear all,

I am looking at the help page for reading json files, but it is too advanced for me to understand...

Can anyone give an easy example where a json file is read into a variable and printing the data structure?

Hugs,
Louise =)

## Annotate a triangle...

I can draw a triangle using the geomtry package:

point(A, 0, 0), point(B, 2, 1), point(C, 2, 0); triangle(T, [A, B, C])
d := draw(T, axes = none, color = black); t := textplot([[.227, 0.60e-1, typeset(theta)], [1.1, 0, typeset(k__2)]])
display(t,d)

The result is as below.

I would like to place the label k2 below the line but negative numbers do not work. I would like to put a label k1 to the right of
the opposite side but there is no room,  and finally I would like to put sqrt(k1^2+k2^2) above the hypotenuse slanted to be
parallel with the hypotenuse if possible.

## Bug in WhittakerW integration

Maple 2016

Bug_in_integrate.mw

M_Iwaniuk

## How to choose a random point...

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?

## Is it possible to read YAML in Maple?...

Hello all,

I have a hash structure with arrays in a YAML file that I would like to read in Maple.

Does there exist a module, so I can read it?

## Why does Maple fail with this?...

When generating the list of all the permutations of  [\$1..10]  we get an error:

combinat[permute]([\$ 1 .. 10]);

Error, (in combinat:-permute) Maple was unable to allocate enough memory to complete this computation. Please see ?alloc

But if the same problem to solve using a simple custom procedure, there is no any problems:

restart;

Permute := proc (L::list)

local n;

n := nops(L);

if nops(L) = 1 then return [L[1 .. 1]] else

[seq(seq([op(p[1 .. k-1]), L[1], p[k .. n-1][]], k = 1 .. n), p = Permute(L[2 .. n]))] end if;

end proc:

L := CodeTools[Usage](Permute([\$ 1 .. 10])):

nops(L);

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