@vv 

Thank you!

@vv 

I had to check the type of sin and similar expressions

@vv 

Indeed, this button is useless :(

@Kitonum 

Thanks, surprisingly easy...

It is desirable to have the full list of changes/improvements in this release with demonstration of new features. For comparison, Wolfram Research describes in details each new release of its software.

Please, clarify you questions.

What do you mean under "transition matrix"?

Yes, it's possible to convert any help page into a worksheet, apply styles and build a new Help System on the base of converted sheets. Interesting workaround, but time-consuming.....

Result is the same. I'll try to reinstall later.

@Carl Love 

Maybe, my installation of Maple is corrupted?

@maple2015 

Please, go tp Tools > Options... > Precision and adjust parameter "Limit expression length to..." or uncheck it.

@tomleslie 

Thank you, this works.....

@acer 

Thank you. I'm aware of other dsolve options. In fact, I solve a multi-point BVP (not presented in the question), reduced to two-point one. Using Array is more appropritate for a number of reasons. And, at last, the question was about a way of calculation of y'' with use of values of a function and y'.

@Kitonum 

Sorry, my question was invoked by mistyping. I accidentally mixed up “numbcomp” and “numbcomb”

Глянул кратко. Не определены функции p(t), q(t), r(t)

@acer 

Than you.
Empty first line has solved the issue.