mthkvv

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6 years, 142 days

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These are questions asked by mthkvv

Hi there.

I noticed that in Maple 2020 default font size of document (Times New Roman 12) looking bigger than in previous versions. How can I make the view the same as in previous versions?

Thank you

Hi there.

How supress this warning in Maple 2020 when I use "e" just like a variable not an exponent:

Warning, if e is meant to be the exponential e, use command/symbol completion or palettes to enter this special symbol, or use the exp function

?

Thank you

Hi there.

I found bugs in covariant differentiation of vectors that defined in another coordinate system. I attached three documents - two of them with bugs and one with normal behavior.

In cov_diff_bug_1.mw I defined Killing vector in Minkowski spacetime. Then I transformed metric and this vector to spherical coordinate system and calculated covariant derivative of vector and obtained symmetric tensor matrix. But for Killing vector it should be antisymmetric.

In cov_diff_bug_2.mw I set metric in spherical coordinate system by hand instead of transformation and obtained zero covariant derivative.

And in cov_diff_no_bug.mw I set metric and vector by hand without any transformation and obtained normal results - antisymmetric covariant derivative and zero sum of two covariant derivatives with rearranged indexes.

So in Maple 2020 coordinate transformation don't doing well in combining with covariant differentiation. But in previous versions of Maple this behavior could be opposite)

I'm asking developers to consider this issues.

Thank you.

cov_diff_bug_1.mw

cov_diff_bug_2.mw

cov_diff_no_bug.mw

 

Hi all,

 

I think the developers should pay attention to this problem.

 

This simple expression with Threads:-Map executed perfectly on my machine with 8-threaded CPU and 16 GB RAM:

Threads:-Map(proc (i) options operator, arrow; ln(i)/2. end proc, [`$`(1 .. 10^7)]);

 

But the similar expression with Grid:-Map never be executed:

Grid:-Map(proc (i) options operator, arrow; ln(i)/2. end proc, [`$`(1 .. 10^7)]);

Maple or freezed, or crashed every time. Although the consuming of memory is not reached even 50%.

 

The similar problem exist for Grid:-Seq too. With `$`(1 .. 3*10^6) Grid:-Map and Grid:-Seq executed normally. With `$`(1 .. 5*10^6) - 50/50. But not with `$`(1 .. 10^7).

 

Is this a real bug of Grid:-Map and Grid:-Seq ?

Or is exist a way to fix this problem?

 

Thanks.

 

Updated:

I got a new error behavior of Grid:-Map in this case instead crash or freeze:

Grid:-Launch(numnodes = 8);

st := time[real](); Grid:-Map(proc (i) options operator, arrow; ln(i)/2. end proc, [`$`(1 .. 10^7)]);

time[real]()-st;

print(`output redirected...`); # input placeholder

`System error, `, "bad id"
2267.482

 

I hope this helps developers to fix this bug.

What is the correct mode of using dsolve/numeric/compile with Grid package?

I've tried a lot of different, but only one turned out to be working is by using Grid:-Seq(dsolve..., i=1).

For example:

...

dsol := Grid:-Seq(dsolve(dsys, numeric, parameters = [bb, qq, prf0, `pθf0`], compile = true, optimize = true, output = listprocedure, maxfun = 0), i = 1):

dsol3 := proc (tt) try dsol[3](tt) catch "cannot evaluate the solution further": tt = 0. end try end proc:

st := time[real]():

A := Array([Grid:-Seq([seq(op(2, [dsol[1](parameters = [b[i, j], q[i, j], pr[i, j], `pθ`[i, j]]), rhs(dsol3(-10^6))]), j = 1 .. sz[2])], i = 1 .. sz[1])]);

time[real]()-st;

example.mw

But this mode not stable and causing to this error very often:

Error, (in dsolve/numeric/SC/preproc) unable to post-link (rc=31), please try again, and if that fails check that your Windows SDK installation is up to date, and compatible with your Windows compiler

How I can fix this problem?

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