Compute the total resistance of n resistors in parallel - new minor version

The Rparallel31 m-file function computes the total resistance of n resistors in parallel.

This m-file function can be used in any area where the total electrical resistance of parallel resistors is required. The only real difference between this version and the old one is that the function now allows a single vector input parameter (row/column) as well as the usual multiple scalar arguments in the old version. Also the code is more compact than before, demonstrates the use of nargin and isvector and has been tested with MATLAB R2011a.

Example usage:
>> z = Rparallel31(1,1,1)
z = 0.3333

>> z = Rparallel31([1;1;1])
z = 0.3333