itsme

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These are questions asked by itsme

or am I missing something?

Consider:

A:=Matrix(2, 2, [1, 4, 5, 1]);
x0:=Vector([2,1]); #initial condition

sol := DETools:-matrixDE(A, t);

M:=(Matrix(convert(sol[1], listlist)));  #convert to modern day Matrix from array that is returned by matrixDE

#the solutoion according to the documentation:

x:=M.x0;

#should match x0 at t=0, but does not:

subs(t=0, x);

 

#using this instead seems to work. But the docs claim this is method is meant to work for constant coeffs.

sol := DETools:-matrixDE(A, t, method=matrixexp);

 

Am i missing something? or is matrixDE not to be trusted (especially in cases where method is not provided)?

as a side note, the documentation is very out of date; claims matrixDE returns Matrix and vector, but these are just the old array types; means LinearAlgebra operations do not work.

 

 

Hi there:

i use Grid:-Map() to run some code on many cores. When I set

Grid:-Setup(numnodes=23);

everything runs fine. When I set (note I have 28 logical cores present):

Grid:-Setup(numnodes=24);

I get the "stack limit reached" message (see attached image below). I've explored setting stack limits to 'unlimited' at the OS level (ubuntu 18.04), as well as setting

kernelopts(stacklimit=infinity)

However, these do not help, and I still end up with the same message.

Any ideas what could be the problem? Also, I am assuming that kernelopts settings get passed to other, spawned kernels, but even if not, I experimented with setting this directly inside the function that gets passed to Grid:-Map()

thanks

 

 

 

 

Is it just me, or did the insert->subsection disappear from the menus in the latest maple??

i'm using 2018.1 on linux.

thanks

Does anyone understand this behavior? Why under some situations the exponential is not explicitly calculated by maple?

issue_matrix_exp.mw

I'm on linux x86_64, using Maple 2017.3

thanks.
 

Code:

restart:

H:=Matrix(4,4, 0):
H[2,3]:=a*exp(I*(b*x+phi)):
H[3,2]:=a*exp(-I*(b*x+phi)):
H;

LinearAlgebra:-MatrixExponential(-I*H); #result as I would expect

H2:=subs(a=0.1, b=0.3, phi=0.1, H); #substitute a few variables

LinearAlgebra:-MatrixExponential(-I*H2); #why does this not work?

H3:=subs(x=0.35, H2); #substitute numerical value for x as well

LinearAlgebra:-MatrixExponential(-I*H3); #now get a result

how would you interpret the solutions to this:

>int(sin(y/2)^2/(x*(x-y)*y^2), x=omega__ir*t..omega__c*t) assuming t::positive, omega__ir::positive, omega__c::positive, omega__c>omega__ir;
 

which leads to the expression shown in the screen shot. In particular, I'm interested in the condition for the solution to be "undefined"

thanks.

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