zlassq.c

来自「算断裂的」· C语言 代码 · 共 120 行

#include "f2c.h"

/* Subroutine */ int zlassq_(integer *n, doublecomplex *x, integer *incx, 
	doublereal *scale, doublereal *sumsq)
{
/*  -- LAPACK auxiliary routine (version 2.0) --   
       Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd.,   
       Courant Institute, Argonne National Lab, and Rice University   
       October 31, 1992   


    Purpose   
    =======   

    ZLASSQ 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.   

    Arguments   
    =========   

    N       (input) INTEGER   
            The number of elements to be used from the vector X.   

    X       (input) DOUBLE PRECISION   
            The vector x as described above.   
               x( i )  = X( 1 + ( i - 1 )*INCX ), 1 <= i <= n.   

    INCX    (input) INTEGER   
            The increment between successive values of the vector X.   
            INCX > 0.   

    SCALE   (input/output) DOUBLE PRECISION   
            On entry, the value  scale  in the equation above.   
            On exit, SCALE is overwritten with the value  scl .   

    SUMSQ   (input/output) DOUBLE PRECISION   
            On entry, the value  sumsq  in the equation above.   
            On exit, SUMSQ is overwritten with the value  ssq .   

   ===================================================================== 
  


    
   Parameter adjustments   
       Function Body */
    /* System generated locals */
    integer i__1, i__2, i__3;
    doublereal d__1;
    /* Builtin functions */
    double d_imag(doublecomplex *);
    /* Local variables */
    static doublereal temp1;
    static integer ix;


#define X(I) x[(I)-1]


    if (*n > 0) {
	i__1 = (*n - 1) * *incx + 1;
	i__2 = *incx;
	for (ix = 1; *incx < 0 ? ix >= (*n-1)**incx+1 : ix <= (*n-1)**incx+1; ix += *incx) {
	    i__3 = ix;
	    if (X(ix).r != 0.) {
		i__3 = ix;
		temp1 = (d__1 = X(ix).r, abs(d__1));
		if (*scale < temp1) {
/* Computing 2nd power */
		    d__1 = *scale / temp1;
		    *sumsq = *sumsq * (d__1 * d__1) + 1;
		    *scale = temp1;
		} else {
/* Computing 2nd power */
		    d__1 = temp1 / *scale;
		    *sumsq += d__1 * d__1;
		}
	    }
	    if (d_imag(&X(ix)) != 0.) {
		temp1 = (d__1 = d_imag(&X(ix)), abs(d__1));
		if (*scale < temp1) {
/* Computing 2nd power */
		    d__1 = *scale / temp1;
		    *sumsq = *sumsq * (d__1 * d__1) + 1;
		    *scale = temp1;
		} else {
/* Computing 2nd power */
		    d__1 = temp1 / *scale;
		    *sumsq += d__1 * d__1;
		}
	    }
/* L10: */
	}
    }

    return 0;

/*     End of ZLASSQ */

} /* zlassq_ */