classq (3) - Linux Manuals
subroutine classq (integerN, complex, dimension( * )X, integerINCX, realSCALE, realSUMSQ)
CLASSQ updates a sum of squares represented in scaled form.
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.
N is INTEGER The number of elements to be used from the vector X.
X is COMPLEX array, dimension (N) The vector x as described above. x( i ) = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.
INCX is INTEGER The increment between successive values of the vector X. INCX > 0.
SCALE is REAL On entry, the value scale in the equation above. On exit, SCALE is overwritten with the value scl .
SUMSQ is REAL On entry, the value sumsq in the equation above. On exit, SUMSQ is overwritten with the value ssq .
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
- September 2012
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