Power series of a scalar function with a vector

[shehry1]

I was trying to expand a scalar function with a power series but it accepts a vector argument. Do I simply use the multivariable power series expansion with the components of the vector acting as the argument OR do I use the single variable power series and take the vector's magnitude in the expansion?

 

[Dick]

You can only expand as a series in the vector's magnitude if the scalar function is only a function of the vector's magnitude (that's it's spherically symmetric). Is it? If not then you need the multivariable power series.