I have 3 numpy arrays, i.e. `x`,`y`,`z`, which each have equal length. Also, matching indices between the 3 numpy arrays form a single set, e.g. `(x[i],y[i],z[i])`. Given `x`,`y`,`z` as known arrays and an arbitrary target set, e.g. `a = [0.0,1.0,2.0]`, is there an efficient numpy-thonic way to compute the index, `i`, that finds the closest single set in `x`,`y`,`z` to `a`?