Unanswered Questions

This page lists MaplePrimes questions that have not yet received an answer

I want to do the substitution f(t) - ff(t) = epsilon for any variable t in Maple:

 

expand(myerror);
    2 f(x - 2 h)   f(x)   3 f(x + 3 h)   2 ff(x - 2 h)   ff(x)
  - ------------ - ---- + ------------ + ------------- + -----
        15 h       6 h        10 h           15 h         6 h

       3 ff(x + 3 h)
     - -------------
           10 h     


NULL;
myfunc := t -> f(t) - ff(t) = epsilon;
 myfunc := proc (t) options operator, arrow, function_assign;

    f(t)-ff(t) = epsilon end proc


algsubs(myfunc(t), myerror);
          2               1        3            
        - -- f(x - 2 h) - - f(x) + -- f(x + 3 h)
          15              6        10           
        ----------------------------------------
                           h                    

               2                1         3             
             - -- ff(x - 2 h) - - ff(x) + -- ff(x + 3 h)
               15               6         10            
           - -------------------------------------------
                                  h                     


NULL;
subs(f(-h*n + x) = 1, ff(-h*n + x) = 0, f(x) = 1, ff(x) = 0, f(h*m + x) = 1, ff(h*m + x) = 0, myerror)*epsilon;
                           4 epsilon
                           ---------
                             15 h   

 

This happens each time I run a long loop.  (2,500 iterations, which takes about 3 hrs to complete)

Maple always hangs (it does not time out on odetest() ). But my question is not about this (as this is something I have to deal with for long time now and mentioned it before many times. May be one day Maplesoft will fix this). 

But I noticed this also.  When Maple hangs, (and it always hangs at least once during this loop), I then click on the button "interrupt the current operation". This does stop the hangs.

Next I do a restart and starts the loop from the loop counter where it hanged in order to continue.  

But It still hangs at that same iteration. I repeate this again, and it still hangs.

Now I close Maple altogether, start Maple again, open same worksheet, and repeat from the same iteration again from where it was at before, now it does not hang.

This tells me that restart and "interrupt the current operation" do not clean everything as expected. Else why only restarting Maple makes it work?

It means mserver.exe (separate process from the frontend) still is caching something related, and that is why it hangs at that iteration.

I can reproduce this each time I run the whole loop from the start.

I can't make a minimal example, since I have no idea where it hangs and why. And it is related to running a long loop.

I just know it hangs when doing odetest() with timeout which never timeout, and it seems random at what iteration it decides to hang.

But my question is really basic here: Does mserver.exe keep any information about the earlier user session/worksheet even after restart ? help says that restarts clear internal memory of the kernel.

Isn't mserver.exe  the Maple kernel? If so, then what could explain that only restarting Maple clears the hang? I am just looking for ideas that could explain this.

This type of problem is the most annoying thing about Maple for me. 

Maple 2020.1 on windows 10.

 


Eigenvector result is changing every time it run.

How to make eigenvectors result the same every time it run?

 

What do I need to do to the "2 + 3" in the attached Document in order to make it evaluate? I know about F5 to switch between Text and Math modes, but that's not enough to get me where I want to be. The "2 + 3" is already in Math mode, but that's not enough to get it to evaluate.

The Document: t.mw

Something goes wrong in this worksheet with old code

Must be corrected
Thanks

fmatrix.mws

Anyone maybe helps me with writing the maple code mentioned in the following pdf.

I want to know about the potential flow around 3D domain.

 

Doc1.pdf

Don't get a DEplot 


 

with(DEtools,DEplot);with(plots,display);

[DEplot]

 

[display]

(1)

 

 

 

init3:=seq([0,k*0.2,0],k=-4..10);

[0, -.8, 0], [0, -.6, 0], [0, -.4, 0], [0, -.2, 0], [0, 0., 0], [0, .2, 0], [0, .4, 0], [0, .6, 0], [0, .8, 0], [0, 1.0, 0], [0, 1.2, 0], [0, 1.4, 0], [0, 1.6, 0], [0, 1.8, 0], [0, 2.0, 0]

(2)

 

The forward plot is p3:

 

p3:=DEplot([sys],[x,y],t=0..2,[init3],x=-3..2,y=-3..2,stepsize=.05,arrows=none,linecolor=black,thickness=1,axes=box,scaling=constrained):

Error, (in f) numeric exception: division by zero

 

he backward plot is np3:

 

np3:=DEplot([sys],[x,y],t=-2..0,[init3],x=-3..2,y=-3..2,stepsize=.05,arrows=none,linecolor=black,thickness=1,axes=box,scaling=constrained):

Warning, plot may be incomplete, the following errors(s) were issued:
   cannot evaluate the solution further left of -.29861232, probably a singularity
Warning, plot may be incomplete, the following errors(s) were issued:
   cannot evaluate the solution further left of -.93147185e-1, probably a singularity
Warning, plot may be incomplete, the following errors(s) were issued:
   cannot evaluate the solution further left of -.23648931e-1, probably a singularity
Warning, plot may be incomplete, the following errors(s) were issued:
   cannot evaluate the solution further left of -.27325542e-2, probably a singularity

 

Error, (in f) numeric exception: division by zero

 

 

display({p1,p2,p3,np3});

Error, (in plots:-display) expecting plot structures but received: {np3}

 

 


 

Download uitzoeken_ode_lesmateriaal_betounes_of_het_werkt.mw

I have been using Maple 2017 but recently upgraded to MacOS Catalina. It doesn't work anymore. I would upgrade to Maple 2020, but worried will I have to upgrade again when the new MacOS 11 comes out? does anyone have any experiece dealing with similar situation on previous MacOS upgrade?

Hi,

How I can solve biharmonic equations in toroidal coordinate?

If this possible I can provide a worksheet and send it.

I provided a solution for Laplacian in pdf file.

Separation_of_Laplace.pdf

 

Dear All,

I am studying parallel programming in Maple. Two words are important keys in parallel programming. The one is “task”, and another is “process”. In the help pages of Maple are said the Grid:-Map package is executed in separate “processes”, while the Threads:-Map command is tried to divide the input into separate “tasks”.

  1. What is the difference between the “process” and “task” conception and meaning in Threads and Grid packages?
  2. What is the discrepancy between Grid:-Map and Threads:-Map commands in the practice and execution?
  3. Between the “process” and “task”, which one of them does have the smaller run-time?
  4. What is the default value of “tasksize” option in Grid:-Map and Threads:-Map commands,
  5. Does or the larger value of the “tasksize” option results in smaller run-time either the smaller value of that?

 

Can anyone explain to me the above questions?

Thanks in advance,

Best wishes

Dear maple users,

Greetings.

When converting the maple figure into EPS format (for latex) which shows white patches.

How to avoid such patches.

does maple provide a way to programatically get the name of the "current" worksheet file?

I'm looking for something analogous to
interface(worksheetdir);

which gives the directory the worksheet file is in.

thanks.

 

Hello everyone.

I am not really sure how to solve the following problem:

Given a parametriaztion of a surface as an interpolation in terms of given nodes as:
X(ξ,η)= Σ Νi(ξ,η) Xi, it is possible to calculate tangent and normal vectors as:
α1(ξ,η)= Σ Νi,ξ(ξ,η) Xi     α2(ξ,η)= Σ Νi,η(ξ,η) Xi  and a3(ξ,η)= cross(a1,a2) and their derivatives
α1,ξ α1,η α2,ξ α2,η etc.
For a variation of Xi i.e.  a variation of X can be calculated δX(ξ,η)= Σ Νi(ξ,η) δXi in terms of 
intermediate quantities that are as simple as  Σ Νi(ξ,η) for the position vector but get quite complicate
for the normal vector (δα3 that depends on a cross product) of given vectors  and for higher order derivatives,
or for the second variation. These variations can be also expressed with a directional derivative in the direction 
X,Y, or Z of a node i with initial position Xi.

To calculate those more complicate derivations I try to express them in terms of known less complicate ones.
Symbolizing r and s the first and second variation, and α,β firs and second derivative withh respect to ξ οr h or ξ,η.


Regarding the variation of the normal vector "a3_t" as known (i.e. a3_t,r)
and the variation of its norm "a3_n" (i.e. a3_n,r) as known too we can get the variation of
the of unit normal using the following commands:

a3 := a3_t(a, s, r)*(1/a3_n(a, s, r)): (vector-scalar operation) (1)
diff(a3, r):

the second variation
diff(a3, r):
diff(diff(a3, r), s) (2)

and even variations of its derivatives 
diff(diff(diff(a3, a), r), s): (3) 

That yield the results of the posted picture.

The problem is that if we want to calculate in the same way the variation of the derivative 
of expressions that involve the vector-vector operations i.e  variation of diff(a3_t, a)
where a3_t = CrossProduct(a1(a,r,s),a2(a,r,s)) it is not possible to do that as in (1)
we cannot substitute CrossProduct or dot product operation  with simple multiplication.

If we use the same strategy in VectorCalculus package we can get some results:
using the following commands: 

a1 := PositionVector([a1x(a, s, r), a1y(a, s, r), a1z(a, s, r)], cartesian[x, y, z])
a2 := PositionVector([a2x(a, s, r), a2y(a, s, r), a2z(a, s, r)], cartesian[x, y, z])
a3T := CrossProduct(a1, a2)
diff(a3T, r)

but then (as it is shown in the upload picture 2) the calculations are performed component-wise
are very lengthy so it is impossible to get second derivative or second derivation.

So I would like to ask is it possible to declare a1 as a vector but not give its components a1x, a1y etc explicitely but instead
declare it as a vector valued function of (a, r, s). so that it yields simpler expressions 
as "a3_t,r= a1,r(x)a2 + a1(x)a2,r".

I would also like to know if those calculations can be made simpler with and another package and if so is there an appropriate example
or a book that explains how to do that.

I would really appreciate  any idea.
Because this is a difficult problem Maple can make it very easy.

Thank you in advance.


upload1.mw

If I have a tensor T[mu,nu,alpha] in 3-dimensions which is symmetric on {mu,nu} and anti-symmetric on {nu,alpha}, then the number of independent components should be zero. However, if I put this into Maple, using Library:-MinimizeTensorComponents followed by Library:-NumberOfIndependentTensorComponents it returns 4.

Any insight into why it does this would be great, thanks.

Hi,

I have been  working on a Maple code written almost 17 years back. The code generates a 3D model input for modelling analysis in ABAQUS software. The input file generated is different from the usual ABAQUS input files. I am seeking help with how to make changes to the input file generated to import into the  ABAQUS. I am uploading the notepad version of the input file as the Maple does not allow .inp files. Please do find the below attachment.

wucell.txt

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