DOUBLE PRECISION FUNCTION DZNRM2(N,CX,INCX)
 
a real*8 function that computes the Euclidean norm of a complex*16
vector, also known as the root-mean-square norm, or the square root
of the sum of the squares of the entries.
DZNRM2:=SQRT(SUM(I=1 to N)DBLE(CX(I))**2+AIMAG(CX(I))**2)
 
N      Input, INTEGER N, number of elements in vector.
 
SX     Input, COMPLEX*16 SX(N), vector whose norm is desired.
 
INCX   Input, INTEGER INCX, increment between elements of SX.  For contiguous
       elements, INCX = 1.
 
DZNRM2 Output, DOUBLE PRECISION DZNRM2, the euclidean norm of the vector SX.