NAME

       classq.f -

SYNOPSIS

   Functions/Subroutines
       subroutine classq (N, X, INCX, SCALE, SUMSQ)
           CLASSQ updates a sum of squares represented in scaled form.

Function/Subroutine Documentation

   subroutine classq (integer N, complex, dimension( * ) X, integer INCX, real SCALE, real SUMSQ)
       CLASSQ updates a sum of squares represented in scaled form.

       Purpose:

            CLASSQ returns the values scl and ssq such that

               ( scl**2 )*ssq = x( 1 )**2 +...+ x( n )**2 + ( scale**2 )*sumsq,

            where x( i ) = abs( X( 1 + ( i - 1 )*INCX ) ). The value of sumsq is
            assumed to be at least unity and the value of ssq will then satisfy

               1.0 .le. ssq .le. ( sumsq + 2*n ).

            scale is assumed to be non-negative and scl returns the value

               scl = max( scale, abs( real( x( i ) ) ), abs( aimag( x( i ) ) ) ),
                      i

            scale and sumsq must be supplied in SCALE and SUMSQ respectively.
            SCALE and SUMSQ are overwritten by scl and ssq respectively.

            The routine makes only one pass through the vector X.

       Parameters:
           N

                     N is INTEGER
                     The number of elements to be used from the vector X.

           X

                     X is COMPLEX array, dimension (N)
                     The vector x as described above.
                        x( i )  = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.

           INCX

                     INCX is INTEGER
                     The increment between successive values of the vector X.
                     INCX > 0.

           SCALE

                     SCALE is REAL
                     On entry, the value  scale  in the equation above.
                     On exit, SCALE is overwritten with the value  scl .

           SUMSQ

                     SUMSQ is REAL
                     On entry, the value  sumsq  in the equation above.
                     On exit, SUMSQ is overwritten with the value  ssq .

       Author:
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Date:
           September 2012

Author

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