Either post your complete Maple input, or upload your worksheet (mw file) so that we can reproduce the problem.

Also, your Maple version may be relevant.

BTW: I have the deleted your (even more incomplete) question with almost the same title.

This has been fixed in Maple 2019: the 1st simplify call now returns 0 (even without the assumption).

I can't comment on the error message, but the is call returns true in the development version of Maple, so it should be fixed in the next release.

Thanks for bringing it to our attention. The bug is already in our database.

@Christopher2222 The old file is no longer available. Same principle as with previous dot releases. If you downloaded it before, we suggest that you delete it locally.

I cannot reproduce that either; tried on Windows 7 here.

The white redrawing artefacts that I see in your video (thanks for embedding it), seem to indicate some Java problem. You might consult our FAQs, particularly https://faq.maplesoft.com/hc/en-us/articles/360019491692-Graphical-glitches-in-Maple.

Please upload a worksheet so that we can reproduce the problem and possibly find a solution. Nobody will type in anything from a screenshot.

@Mac Dude AFAIK, it was tested on all supported versions. Personally, I tested it on an iPad Air with iOS 12.4, which works well. Please send a detailed report (i.e. with hardware and software specs) to support@maplesoft.com. Thanks!

Update: you can also send feedback via https://www.maplesoft.com/products/MapleCompanion/feedback.aspx.

Could you clarify what kind of simplification you have in mind, and how it is related to the GCD? (And the GCD of which polynomials - you mentioned only one...)

Ideally, upload a worksheet, or - if the example is small - post it as plain text so that we can copy&paste it.

For grouping coefficients, take a look the collect command.

Side remark: The NumberTheory package introduced in Maple 2016 comes with a CalkinWilfSequence routine.

@acer The language settings of Windows were relevant here: the bug appeared for (all?) non-English versions.

Anyway, it is fixed by now, and there was an easy workaround, as others have pointed out.

Side remark: Maple 2016 introduced a PCA command in its Statistics package. Perhaps that is useful for you as well. I haven't looked at your worksheet, though.

@Zeineb Sure, that will yield _C1=12. Plotting over any y range is trivial then.

@tomleslie Thorough and helpful answer, as always. :-)

Just let me add that Maple offers CodeGeneration:-Matlab for exporting Maple code, and (to some extent) even the opposite direction: importing MATLAB code into Maple via Matlab:-FromMatlab and related routines. Perhaps the OP should give the latter try.

@student_md This pdetest result is actually a list, not a matrix. The solution is applied (i.e. differentiated and then plugged into) the list of equations, that is [PDE, BCs, ICs], where BCs is a sequence of two equations in this example.
If you don't need the multiplicity info, use sets instead of lists. Simply replace the square brackets by curly braces then. However, if any non-zero result occurs, lists are helpful in pinpointing the equation that led to that result.
Please look up the ?pdetest help page for more details.

Side remarks, unrelated: pdsolve and pdetest are top-level commands, hence loading PDEtools is unnecessary here.

And helping pdsolve with the multiplicative ansatz (by providing one of the two factors) leads to the PDE (not the full IBVP!) being solved:

sol:=pdsolve(PDE,HINT=exp(-t)*g(x));
sol:=pdsolve(PDE,HINT=f(t)*sin(x));

However, that requires too much knowledge about the solution, so I would see this more as an observation rather than a valid workaround.

I'm afraid nobody is going to type in those equations for you. (Smart community!)

For a start, please see the examples on the ?pdsolve help page. The diff syntax and semantics are fairly simple. Some keystrokes can be saved by using the diff_table command from the PDEtools package.

You should also give the new Maple Companion App a try!