This

expr:='1/r^2*diff(r^2*diff(v(r),r),r)'

gives

And when evaluated second time it gives

expr

The question is, how to put expr back to its original form shown at the top?

I tried simplify, combine, etc.. but nothing puts back to same form.

The reason I am asking, is that I need put more complicated expression in form that resembles when I am looking at in textbook. For an example, the Laplacian

VectorCalculus:-Laplacian(u(r,theta,phi),'spherical'[r,theta,phi])

But the above should be the same as

So I figured if I can rewrite each term to look like in the shorter version above (complete derivative version), it will be easier for me to compare what Maple gives and the text book shows,

ps. I found that the following command in Maples gives a little clearer Laplacian, but it is still not as simplified as the book but it is better than using VectorCalculus:-Laplacian

Physics[Vectors]:-Laplacian(u(r,theta,phi));

At least this has each term a little more seprated.

When typing 

z:=exp(I*2*Pi/3);
convert(z,'sincos')

Maple evaluates the intermediate result which is cos(2*Pi/3)+I*sin(2*Pi/3) and  gives

Is there a way to tell it not to do this? I'd like to see the result as when typing

'cos(2*Pi/3)+I*sin(2*Pi/3)'

Is there an option or method to tell Maple not to immediate evaluation in the above? it can do evaluate next time the expression is used.

Should Maple handle this error internally and may be give no solution if it can't solve it instead of this  error?

When setting boundary condition to zero, maple gives error below. Heat PDE in a sphere. No angle dependency. Only the radial part.

unassign('r,u,t');
pde:=diff(u(r,t),t)= 1/r*diff(r*u(r,t),r$2); #Laplacian in spherical
ic:=u(r,0)=1;
bc := u(1,t) =0;
pdsolve([pde,ic,bc],u(r,t),HINT =boundedseries(r=0)) assuming t>0

Error, (in assuming) when calling 'ln'. Received: 'when calling 'ln'. Received: 'numeric exception: division by zero''

Adding assumptions such as 0<r,r<1 did not help.

Physics version 348. Maple 2019 on windows 10. Is there something I am doing wrong? 

Why does Maple display eval(diff(f(r),r),r=C)=0;  differently when C is a number?

unassign('f,C,r');
eval(diff(f(r),r),r=C)=0;
eval(diff(f(r),r),r=5)=0;

I wanted the first one to display the same as the second one. First one looks confusing. it looks like taking derivative w.r.t to C. Is there a way to make the first one look like:

I am learning how to use dchange in Maple. I can do  something as dchange(x=t^2) OK, but I need to do dchange(x=t^n) where "n" is meant to be a parameter that I can later use subs on to set it to any number I want.  But I do not know how to tell Maple that "t" is the new variable and that "n" is meant to be used as constant or parameter.

As an example, this works

n:=2;
ode:=x^2*diff(z(x),x)=0;
PDEtools:-dchange({x=t^n},ode,{t})

But this does not work

n:='n';
ode:=x^2*diff(z(x),x)=0;
PDEtools:-dchange({x=t^n},ode,{t});
subs(n=2,%)

It used "n" above as new variable. So the dependent variable which was z(x) became z(t,n). 

So I need to tell Maple that "t" is the new variable only and not "n" as well. 

Is it possible to do this in Maple?

Maple 2019 on windows.