x^2 + y^2 - z^2 = 1
z^2 - x^2 - y^2 = 1

r^2 - z^2 = 1
z^2 - r^2 = 1

r^2 = 1 + z^2
z^2 = 1 + r^2

r = sqrt(1 + z.^2)
z = sqrt(1 + r.^2)