root / src / blas / dznrm2.f @ 7
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DOUBLE PRECISION FUNCTION DZNRM2(N,X,INCX) |
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* .. Scalar Arguments .. |
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INTEGER INCX,N |
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* .. |
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* .. Array Arguments .. |
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DOUBLE COMPLEX X(*) |
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* .. |
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* |
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* Purpose |
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* ======= |
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* |
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* DZNRM2 returns the euclidean norm of a vector via the function |
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* name, so that |
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* |
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* DZNRM2 := sqrt( conjg( x' )*x ) |
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* |
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* |
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* -- This version written on 25-October-1982. |
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* Modified on 14-October-1993 to inline the call to ZLASSQ. |
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* Sven Hammarling, Nag Ltd. |
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* |
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* |
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* .. Parameters .. |
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DOUBLE PRECISION ONE,ZERO |
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PARAMETER (ONE=1.0D+0,ZERO=0.0D+0) |
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* .. |
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* .. Local Scalars .. |
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DOUBLE PRECISION NORM,SCALE,SSQ,TEMP |
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INTEGER IX |
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* .. |
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* .. Intrinsic Functions .. |
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INTRINSIC ABS,DBLE,DIMAG,SQRT |
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* .. |
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IF (N.LT.1 .OR. INCX.LT.1) THEN |
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NORM = ZERO |
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ELSE |
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SCALE = ZERO |
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SSQ = ONE |
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* The following loop is equivalent to this call to the LAPACK |
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* auxiliary routine: |
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* CALL ZLASSQ( N, X, INCX, SCALE, SSQ ) |
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* |
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DO 10 IX = 1,1 + (N-1)*INCX,INCX |
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IF (DBLE(X(IX)).NE.ZERO) THEN |
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TEMP = ABS(DBLE(X(IX))) |
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IF (SCALE.LT.TEMP) THEN |
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SSQ = ONE + SSQ* (SCALE/TEMP)**2 |
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SCALE = TEMP |
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ELSE |
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SSQ = SSQ + (TEMP/SCALE)**2 |
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END IF |
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END IF |
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IF (DIMAG(X(IX)).NE.ZERO) THEN |
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TEMP = ABS(DIMAG(X(IX))) |
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IF (SCALE.LT.TEMP) THEN |
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SSQ = ONE + SSQ* (SCALE/TEMP)**2 |
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SCALE = TEMP |
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ELSE |
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SSQ = SSQ + (TEMP/SCALE)**2 |
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END IF |
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END IF |
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10 CONTINUE |
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NORM = SCALE*SQRT(SSQ) |
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END IF |
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* |
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DZNRM2 = NORM |
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RETURN |
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* |
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* End of DZNRM2. |
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* |
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END |