I have differential equation with x as independent variable that I want to convert to state space representation.

But DynamicSystems will not accept y(x) as the output variable, since it defaults to y(t).

Help under "Description of the Model of a Linear System Object" says it is possible to change the independent variable by changing continuoustimevar setting. But help does not give an example how to do this and all my tries failed.

How to do this? Attached is worksheet showing the problem

Download DS_problem.mw

Using t=0 .. 3*Pi the plot is truncated. Changing the 3*Pi to a number, then the full plot shows.

Also keeping 3*Pi but changing y=-1..1 to y=-1.01 .. 1.01 now the full plot shows again.

Is the above normal behaviour or it it a bug?

Download strange_result_of_DEplot.mw

Given two terms in expression of type  `+` where the first is rational and the second is not, I wanted to combine both under on common denominator to obtain one term (not `+` any more).

I expected that combine will do that.

restart;
expr:=A/B+C;
combine(expr);

But the above leaves the original expression as is. Ofcourse I can just do

numer(expr)/denom(expr);

Here is screen shot

My question is why combine does not do that automatically? For reference, Mathematica command Together is the equivalent to Maple combine and this is what it does

Which is what one would expect to happen. 

I am just trying to understand the logic why Maple's combine did not work as one would expect. That is all. I looked at help and tried different option to combine, but non worked.

Maple knows how to obtain differntials using D.

So typing  D(x*y) it gives   D(x)*y+x*D(y)

But what I want is given as input  D(x)*y+x*D(y) have Maple return back D(x*y)

Nothing I tried work. I tried simplify and convert(...,D) 

I am looking for a function that takes an expression with differentials like the above output, and return, if possible ONE differnetial in the form  D(  f(x,y) )

What I mean, given as INPUT any of these expressions on the RHS in the image below

To return back  the  D(...)  in the LHS above. I know Maple can do it going from the LHS to the RHS. But I want the other way around.

Does Maple support such operations?

Maple 2022.1

To Maple support,. 

fyi,

internal error generated on this ode when trying odetest
 

Download problem_odetest_july_23_2022.mw

Update 2 years later

FYI, This error is still not fixed in Maple 2024

Download odetest_error_series_august_2024.mw

Will check again in 2-3 years and I am sure this bug will still not be fixed.