| 1 | DOUBLE PRECISION FUNCTION DZNRM2(N,X,INCX) |
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| 2 | * .. Scalar Arguments .. |
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| 3 | INTEGER INCX,N |
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| 4 | * .. |
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| 5 | * .. Array Arguments .. |
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| 6 | DOUBLE COMPLEX X(*) |
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| 7 | * .. |
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| 8 | * |
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| 9 | * Purpose |
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| 10 | * ======= |
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| 11 | * |
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| 12 | * DZNRM2 returns the euclidean norm of a vector via the function |
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| 13 | * name, so that |
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| 14 | * |
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| 15 | * DZNRM2 := sqrt( conjg( x' )*x ) |
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| 16 | * |
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| 17 | * |
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| 18 | * -- This version written on 25-October-1982. |
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| 19 | * Modified on 14-October-1993 to inline the call to ZLASSQ. |
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| 20 | * Sven Hammarling, Nag Ltd. |
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| 21 | * |
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| 22 | * |
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| 23 | * .. Parameters .. |
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| 24 | DOUBLE PRECISION ONE,ZERO |
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| 25 | PARAMETER (ONE=1.0D+0,ZERO=0.0D+0) |
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| 26 | * .. |
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| 27 | * .. Local Scalars .. |
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| 28 | DOUBLE PRECISION NORM,SCALE,SSQ,TEMP |
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| 29 | INTEGER IX |
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| 30 | * .. |
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| 31 | * .. Intrinsic Functions .. |
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| 32 | INTRINSIC ABS,DBLE,DIMAG,SQRT |
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| 33 | * .. |
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| 34 | IF (N.LT.1 .OR. INCX.LT.1) THEN |
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| 35 | NORM = ZERO |
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| 36 | ELSE |
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| 37 | SCALE = ZERO |
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| 38 | SSQ = ONE |
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| 39 | * The following loop is equivalent to this call to the LAPACK |
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| 40 | * auxiliary routine: |
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| 41 | * CALL ZLASSQ( N, X, INCX, SCALE, SSQ ) |
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| 42 | * |
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| 43 | DO 10 IX = 1,1 + (N-1)*INCX,INCX |
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| 44 | IF (DBLE(X(IX)).NE.ZERO) THEN |
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| 45 | TEMP = ABS(DBLE(X(IX))) |
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| 46 | IF (SCALE.LT.TEMP) THEN |
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| 47 | SSQ = ONE + SSQ* (SCALE/TEMP)**2 |
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| 48 | SCALE = TEMP |
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| 49 | ELSE |
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| 50 | SSQ = SSQ + (TEMP/SCALE)**2 |
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| 51 | END IF |
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| 52 | END IF |
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| 53 | IF (DIMAG(X(IX)).NE.ZERO) THEN |
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| 54 | TEMP = ABS(DIMAG(X(IX))) |
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| 55 | IF (SCALE.LT.TEMP) THEN |
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| 56 | SSQ = ONE + SSQ* (SCALE/TEMP)**2 |
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| 57 | SCALE = TEMP |
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| 58 | ELSE |
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| 59 | SSQ = SSQ + (TEMP/SCALE)**2 |
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| 60 | END IF |
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| 61 | END IF |
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| 62 | 10 CONTINUE |
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| 63 | NORM = SCALE*SQRT(SSQ) |
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| 64 | END IF |
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| 65 | * |
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| 66 | DZNRM2 = NORM |
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| 67 | RETURN |
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| 68 | * |
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| 69 | * End of DZNRM2. |
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| 70 | * |
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| 71 | END |
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