21448 Reputation

29 Badges

15 years, 120 days

Social Networks and Content at

MaplePrimes Activity

These are replies submitted by acer

@digerdiga Which version and operating system are you using? 

@Carl Love My guesses are:

LWM = Legendre wavelet operational matrix method

NFSD = Nonstandard Finite Difference

@sand15 You might also be interested in examples like these:

w := (a-2)/(a-4^(1/2)):

eval(w, a = 2);  # notice


limit(w, a = 2);

f := a -> (a-4)/(2-sqrt(a)):

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

ee := f(a);

                  a - 4
          ee := --------
                 2 - a

eval(ee,a=4);  # notice




See here for an old discussion.

@tomleslie In the Standard Java GUI, for a call to the interface command to work properly it has to be in a separate Execution Group (or Document Block) from a restart.

I took the liberty of fixing the rtablesize MapleNet property in the file and inlining it above. I hope that's ok.

@ALIKHADEMI Put your followup details here. I'll delete duplicate posts of this.

If you're trying to export to Matlab or Excel then write your data to a Matrix and use the ExportMatrix command.

Upload your worksheet if you want us to fill in the missing bits.

Did you intend that restart?

Earlier, you had defined a polynomial in p (assigned to v?). The restart gets rid of that. Perhaps you just forgot to assign it again.

@das1404 My answer already demonstrated how the terms in the lhs (or rhs) of an equation could be reduced by common constant content. The `simplify` command doesn't do that.

If you want an answer to some specific question then ask a specific question.

@Ronan At nelems=10^9 I would not be surprised if your 64GB machine starting swapping of RAM, and if that happens then you might as well stop the run as you'll be timing your OSes ability to swap rather than Maple's ability to compute.

But why bother storing the results in an Array anyway? You could compute them without assigning them to anything, and measure the timing of that.

@Ronan So you got 400sec for nelems=100mil it seems, with this code.

Not a bad speedup from  approx. 1530sec.

One aspect to note is that 300 of those 400 seconds are spent in the garbage collector. I wonder how much allocated memory it'd take to hold any of these examples if gc were (somehow) effectively turned off. I suppose the answer to that is the final value of kernelopts(bytesused) and is likely prohibitively high.

If we subtract the realgctime from the realtime for your 10mil and 100mil runs with the (so far) optimal code then the following observation can be made.

   10mil:    realgctime = 7sec         (totalrealtime-gcrealtime) = 10sec

  100mil:   realgctime = 300sec     (totalrealtime-gcrealtime) = 100sec

So the real time to do the actual computations went up by a factor of 10 (from 10sec to 100sec) as the problem size went from 10mil to 100mil. That's even better than I'd have guessed, since the maximal exponent goes up with problem size for your example. But the garbage collection real time went up by a factor of 42 (from 7sec to 300sec), which is noticeably higher. I don't know whether that could be mitigated.

@nm On MS-Windows you could look for something like,


(It's a little confusing because, on MS-Windows, the name of this preferences/resource file is like the name of a Maple initialization file. But the locations are different. And only the latter contains actual Maple source code.)

@Chouette You can fill out this Software Change Request (SCR) form. You can get to it from the Mapleprimes top menu.

@mmcdara I constructed the example so that the denominator would be (mathematically equivalent to) zero upon the substitution x=5 .

At the top-level I used 1-level evaluation in order to print it without the denominator becoming zero. Within a procedure that printing can be done directly since access of the procedure's assigned locals only gets 1-level evaluation.

The purpose was to prevent the evaluation of GAMMA(10/3) after the substitution x=5. After evaluation of that GAMMA(10/3) call the whole denominator would become zero. Hence accessing the evaluated, substituted expression would produce a numeric exception.



eval(GAMMA(10/3), 1);


And so,

expr := 1/(GAMMA(x*2/3)-56*Pi*sqrt(3)/(81*GAMMA(2/3)));




TD := subs(x=5, denom(expr));




eval(TD, 1);


lprint(eval(TD, 1));


I just happened to utilize lprint so that the output was terse. At the top-level I could call lprint or print after the substitution by using 1-level eval of the argument to prevent the division by zero that would occur upon full evaluation. Within the procedure I could utilize lprint or print directly.

The goal was to illustrate that utilizing subs can incur additional risk of hiding a zero-valued denominator, and that the situation can be trickier still if it happens within a procedure.

@Ronan You've probably already noticed that there can be noticeable variation in timing even for repeats of the very same method.

So it gets a little tricky to compare, when the average between two methods is on the same order as the variation. Just wanted to mention it.

@mmcdara I was mostly thinking of the ways in which the lack of evaluation can cause surprises (later on).


expr := 1/(GAMMA(x*2/3)-56*Pi*sqrt(3)/(81*GAMMA(2/3))):

T := subs([x=5], expr):



# It's inconvenient to be surprised by this only later. Eg.

Error, numeric exception: division by zero

# It may not be evident, that the problem is this:

Error, numeric exception: division by zero

# It's often convenient to find out sooner.
eval(expr, [x=5]);

Error, numeric exception: division by zero

# Inside a procedure the local `T` sent to `print`
# is only evaluated 1-level, and the problem can be
# missed.
F := proc()
  local expr, T;
  expr := 1/(GAMMA(x*2/3)-56*Pi*sqrt(3)/(81*GAMMA(2/3)));
  T := subs([x=5], expr):
  print(T); # non-useful debug attempt
end proc:





Perhaps this will provide background.

First 80 81 82 83 84 85 86 Last Page 82 of 450