Does this formula for directional derivative always hold as long as all the partials exist?
93967
Prove partial derivatives exist, but not all directional derivatives exists.
33691
Confusion about a particular differential form being exact?
53841
Function always continuous in a Sobolev Space?
41043
example of discontinuous function having direction derivative
53640
Equality of mixed partial derivatives
52701
Manipulating Partial Derivatives of Inverse Function
124499
Where is the error in my proof that all derivatives are continuous?
151297
Second order partial of $f(x,y)=\frac{xy(x^2-y^2)}{x^2+y^2}$
48464
If the derivative approaches zero then the limit exists
111611
When can we add a total time derivative of $f(q, \dot{q}, t)$ to a Lagrangian?
68752
A few questions about infinite derivative.
45071
Having the derivative be an operator
40184
Notation in partial differentiation
11205
Computing second partial derivative with polar coordinates
24449
How discontinuous can a derivative be?
81411
why normalize and the definition of directional derivative
45363
Show that both mixed partial derivatives exist at the origin but are not equal