SLAPY3 - return sqrt(x**2+y**2+z**2), taking care not to
cause unnecessary overflow
REAL FUNCTION SLAPY3( X, Y, Z )
REAL X, Y, Z
SLAPY3 returns sqrt(x**2+y**2+z**2), taking care not to
cause unnecessary overflow.
X (input) REAL
Y (input) REAL Z (input) REAL X, Y and
Z specify the values x, y and z.