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These are questions asked by DarkMath


How one can plot a vector (field) defined in Physics[Vectors] package ?

F_:=r _r + phi^2 _phi

I could normally use fieldplot/fieldplot3d from plots package to plot vector fields from VectorCalculus package, but with Physics[Vectors] package, I am not sure how to plot these. Can you show me a way to plot Physics[Vector] vectors?



I was wondering if it is possible to write a 1st order differential equation in differential form?


Instead of writing the diff eq in 


is it possible to to write something like

ode: -(x^2+x*y(x))*D(x)+ (1)*D(y(x))=0


When I create a rooted vector 


and a free vector


and dot product them


it gives me 2.

But if I change v1 to 


the product of v1.v2 gives me an error

"..cannot combine two rooted vectors with different points of origin"

Can anyone explain me the problem? 

Here is what I understand: 

In spherical coordinates the unit vector e_r, e_th, e_ph are functions of theta and phi. So when I call root=[1,Pi/4,0] that means r=1, theta=Pi/4 and phi=0. This uniquely defines the unit vectors in spherical coordinates and r places the vector away in the e_r direction. The [0,0,1] then attaches a vector to the point r=1, theta=Pi/4 and phi=0  with only 1 unit along the e_ph direction.

What I don't understand is the concept of origin with the free vector and the rooted vector. How changing the theta from Pi/4 to Pi/6 makes the origin "different"? 

Edit: This is part of the VectorCalculus pacakge.


I tried to solve an inequality involving factorials using solve, but I failed. The code is 


n should be 7.

Maple returns me "Warning, solutions may have been lost" message. 

How can I solve an inequality like this using solve?

I worked around this with a for loop testing the value of the expression for every increasing value of n against the criteria. Is there a "magical" keyword that will help with solve? 




How can I use assmptions in partial differential equations?

For example consider the following differential equation

sol:=pdsolve(pde,build) assuming alpha=0

This gives me the same solution if alpha!=0

I also tried this


I again got the same result as if alpha!=0. Except this time there was a tilde on the right side of alpha (to my knowledge that means there are assumptions on alpha)

How do you apply assumptions in PDEs? 



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