nm

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These are questions asked by nm

Any one know if it possible to see the steps used by the limit() function as one does with many other functions such as dsolve and int ?  This is what I tried

restart;
infolevel[limit]:=5;
interface(verboseproc=3);
limit(x^2 *log(x),x=0);

But I see no steps, only the final answer. Are not all Maple functions possible to trace? How does one know which functions can generate trace and which do not?

I am using Maple 2016.1

I wanted to see something like:

let x=1/t, hence expression becomes  (-ln t)/t^2, now taking limit as t->infinity. Applying L'Hopital rule, limit t->infinity of -1/(2 t^2) which gives zero.

I assumed this is something what Maple does internally, (but there are other ways also) and wanted to see what Maple does.

 

I have never seen DEtools:-odeadvisor hang before. I've seen dsolve itself hang many times, but not odeadvisor. Is this a bug? Maple 2016.1 on windows.

restart;
eq:=(2*y(x)*diff(diff(y(x),x),x)-diff(y(x),x)^2)^3+32*diff(diff(y(x),x),x)*(x*diff(diff(y(x),x),x)-diff(y(x),x))^3 = 0;
DEtools:-odeadvisor(eq);

Now it hangs. Waited for more than one hr. This is an ODE from a book. Do others see the hang as well?

 

The ODE diff(y(x),x) = sec(x)^2*sec(y(x))^3  can be solved as separable. So the answer should be 

simple_answer:=sin(y(x))*(cos(y(x))^2+2)=C_1+3*tan(x);

as can be seen by direct integration of each side of the differential equation. I am trying to make Maple give the same answer, but not having any luck. 

restart;
ode:=diff(y(x),x) = sec(x)^2*sec(y(x))^3;
sol:=dsolve(ode, y(x),implicit);

I tried simplify(sol,trig) and tried simplify(sol,size).  Both Maple answer, and the simple answer solve the ODE.

Is there a way to make Maple dsolve give the simpler answer, or simplify/convert the answer it gives to the simpler one? I am newbie in Maple.

Hello; I found another ODE which Maple gives division by zero on.  Is this also a bug? 

dsolve(x*(a^2*x+(x^2-y(x)^2)*y(x))*diff(y(x),x)^2-(2*a^2*x*y(x)-(x^2-y(x)^2)^2)*diff(y(x),x)+a^2*y(x)^2-x*y(x)*(x^2-y(x)^2) = 0, y(x));

Error, (in dsolve) numeric exception: division by zero

This is from a book. Using Maple 2016.1 on windows.

Maple 2016.1 on windows. This ODE from a book, and Maple gives division by zero. Is this a bug or expected?

ode:=(a^2*x+(x^2-y(x)^2)*y(x))*diff(y(x),x)+x*(x^2-y(x)^2) = a^2*y(x);
dsolve(ode, y(x));

Error, (in dsolve) numeric exception: division by zero


Mathematica gives this to same ODE, but no division by zero.

DSolve[x*(x^2 - y[x]^2) + (a^2*x + y[x]*(x^2 - y[x]^2))*y'[x] == a^2*y[x], y[x], x]

Solve[x^2/2 - (1/2)*a^2*Log[x - y[x]] + (1/2)*a^2*Log[x + y[x]] +y[x]^2/2 == C[1], y[x]]

Where is the division by zero coming from in Maple?

2016.1 on windows.

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