DLAPY2 - return sqrt(x**2+y**2), taking care not to cause
unnecessary overflow
DOUBLE PRECISION FUNCTION DLAPY2( X, Y )
DOUBLE PRECISION X, Y
DLAPY2 returns sqrt(x**2+y**2), taking care not to cause
unnecessary overflow.
X (input) DOUBLE PRECISION
Y (input) DOUBLE PRECISION X and Y specify
the values x and y.