hi,i want to take differential with respect to another differential using physics package,but using D instead of diff,could anyone help me do that ? for example :

restart; with(Physics):
A1 := -(1/24)*1*rho*((diff(phi[1](x, t), t))^2)*(h^3)-(1/2)*1*rho*((diff(u[ref](x, t), t))^2)*h-(1/2)*rho*((diff(w(x, t), t))^2)*h+(1/24)*1*1*((diff(phi[1](x, t), x))^2)*(h^3)+(1/2)*1*(1*((diff(u[ref](x, t), x)+(1/2)*(diff(w(x, t), x))^2)^2)+K*1*((diff(w(x, t), x)+phi[1](x, t))^2))*h-1*q*w(x, t):

A2:=-diff(diff(A1,diff(u[ref](x,t),x)),x);

here i want to compute A2 using D command,not diff and i do not want use convert command ! i just need to calculate A2 directly using D command. tnx for your help.

i want to solve this pde,but i do know how to write my boundary or initial conditons,actually my dependent variables were x and y, i changed x to t,since i faced an error that pde solver needs time=varname , but i could not solve my problem,do anyone know how to insert my boundary conditions ?! please help,thnx
maple.mw

i have 3 equations which contains both numeric and symbols, how can i seprrate these to ?
for example :

> restart:
> eq1:=a[1]^3+a[2]+a[3]^2+50;

> eq2:=a[1]^2+5*a[2]+a[3]+44;

> eq3:=a[1]+a[2]+a[3]^2+74;

i want maple to seprate these three equations in two vectors,first vector including symbols and second one includes numerics , like this :
V1:=<<a[1]^3+a[2]+a[3]^2>,<a[1]^2+5*a[2]+a[3]>,<a[1]+a[2]+a[3]^2>>;

V2:=<<50>,<44>,<74>>;

eq:=<<eq1>,<eq2>,<eq3>>;

so that 

is(V1+V2=eq);

gives me the answer true.
tnx for help.

i do not want maple to round off some terms , for example 1.7777777777 which is rounded off 1.7777777778 . i do not want maple to round off the result,what should i do ?

how can i define an index for a vector?

for example i have

V:=Vector(5)

for i to 20 do
...
V[i]=..

od.

when i write V[i] i want to address it for  "i"'s number from the loop,not element "i" of the Vector. how can i define it ?!
thnx for help