@Christian Wolinski I think that you just inadvertently gave two identical commands.

@Christian Wolinski 

As far as I can tell, the 4 light models are just white lights from 4 different angles, and that's the way that they've always been. If you want colored lights, you need to make your own, which is pretty easy.

Shining a white light perpendicularly on a grey surface essentially makes it white. (Note that there's no essential difference between a standard "silver" mirror and a glossy grey one.)

If you execute this, do you see the difference (without doing any mouse manipulation!)?

plot3d(0, 0..1, 0..1, lightmodel= none, orientation= [80, 30, -36]);

plot3d(0, 0..1, 0..1, lightmodel= light3, orientation= [80, 30, -36]);

@chinthak I noticed several things in your code that could be done more elegantly and much, much more efficiently. For example, you do the operation below many times for different sets: 

k := {};
for i from 1 to 4096 do
    if lhs(cyclicsolution[i]) <> rhs(cyclicsolution[i]) then 
        k := {cyclicsolution[i], op(k)} 
    end if
end do:
kk:= cyclicsolution minus k;

That whole block of code can be replaced by the single command:

(kk, k):= selectremove(evalb, cyclicsolution):

In particular, note that 

• no initialization of k is needed;
• no index variable i is needed; indeed, no indexing at all is needed;
• no knowledge of the number of elements of cyclicsolution is needed;
• a single command creates both a set and its complement.

I haven't timed it, but I wouldn't be surprised if my version runs 1000 times faster.

This loop:

numelems(equals);
ind_comp := {};
for i from 1 to 69 do
    ind_comp := {lhs(equals[i]), op(ind_comp)}
end do:

can be replaced by

ind_comp:= lhs~(equals):

@eithne I just checked (1:50 AM, EST, 21-Nov-2019), and the Maple 2019.2 update is still available, ready to be downloaded by unsuspecting users who don't read MaplePrimes (which, I guess, is the majority). This bug is crippling and catasthropic, so why hasn't the update been taken down? Is this an attempt at corporate suicide?

@chinthak 

Oddly enough, nearly the same commands do it in reverse. Forget about solutionlist; it's totally unnecessary. Create the tensor directly from solutions:

T:= eval(Array((1..4)$6, ()-> index(S, args)), solutions);

That's all there is to it!

I know nothing about this nightmare with the update Maple 2019.2 other than what I've read here on MaplePrimes. (Fortunately, I didn't update my own Maple.) The problem that you describe seems consistent with what I've read. And, according to what I've read, you can work around the bug by removing the restart command from your worksheet. IMO, this is the most catasthropic bug ever released into Maple. That leads me to believe that it'll be fixed soon.

@chinthak Ah, yes, I now see the ambiguous interpretations of your Question as essentially being opposites.

To answer, I need to know how the list is organized. In other words, which indices of the tensor correspond to the n^th list element? The easiest situation would be that the indices are the base-4 representation of n-1 with each digit increased by 1.

Or perhaps your list entries already contain the indices in some form?

@SaeedAF7 Thank you, and a Vote Up. It's exactly what I was looking for. 

@rameen hamood 

More hints:

4. The results of any command can be made into a set by enclosing the command in curly braces { }.

5. Any command can be made to operate elementwise, e.g. individually on the elements of a set, by appending ~ to its name, e.g. abs~.

6. The non-real roots of a real polynomial always occur as conjugate pairs. The members of such a pair have the same modulus. 

@acer Thank you for the clarification; I was suspicious of that. I should probably not try understanding unformatted 2D ASCII output on my phone. 

@acer Ouch, the syntax of that undocumented command is a nightmare. Hopefully that gets completely redone before it's ready for "prime time". Consistency demands at the very least that it be convert, not eval, and that the arguments be interchanged.

@Rouben Rostamian  Thank you, and a Vote Up; that's quite informative. I wasn't previously aware of the importance of the distinction between the magnitudes and their ratios.

@SaeedAF7 The question that I just posed to Rouben in a Reply above I also pose to you. Although I don't have MapleSim, just seeing the animation here would sate my curiosity.

@Rouben Rostamian  Just curiousity here: I know that if the cylinders were hollow (and, for simplicity, let's say uncapped), their moments of inertia would be different. How would this affect the plot? For simplicity, let's say that the cylinders are made from sheets of a dense metal of neglible thickness.

@Stretto You cannot change kernelopts(homedir). You may be confusing that with currentdir(...), which can be readily changed with 

currentdir("whatever"):

If you use colons to suppress the output of commands in the initialization file, then their output will not show in your worksheet.