classq.f(3)

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 (integerN, complex, dimension( * )X, integerINCX, realSCALE, realSUMSQ)

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

Definition at line 107 of file classq.f.

Author

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