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| 1 | DOUBLE PRECISION FUNCTION DNRM2(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 PRECISION 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 | * DNRM2 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 | * DNRM2 := sqrt( 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 DLASSQ. |
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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 ABSXI,NORM,SCALE,SSQ |
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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,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 IF (N.EQ.1) THEN |
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| 37 | NORM = ABS(X(1)) |
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| 38 | ELSE |
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| 39 | SCALE = ZERO |
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| 40 | SSQ = ONE |
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| 41 | * The following loop is equivalent to this call to the LAPACK |
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| 42 | * auxiliary routine: |
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| 43 | * CALL DLASSQ( N, X, INCX, SCALE, SSQ ) |
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| 44 | * |
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| 45 | DO 10 IX = 1,1 + (N-1)*INCX,INCX |
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| 46 | IF (X(IX).NE.ZERO) THEN |
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| 47 | ABSXI = ABS(X(IX)) |
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| 48 | IF (SCALE.LT.ABSXI) THEN |
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| 49 | SSQ = ONE + SSQ* (SCALE/ABSXI)**2 |
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| 50 | SCALE = ABSXI |
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| 51 | ELSE |
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| 52 | SSQ = SSQ + (ABSXI/SCALE)**2 |
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| 53 | END IF |
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| 54 | END IF |
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| 55 | 10 CONTINUE |
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| 56 | NORM = SCALE*SQRT(SSQ) |
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| 57 | END IF |
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| 58 | * |
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| 59 | DNRM2 = NORM |
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| 60 | RETURN |
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| 61 | * |
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| 62 | * End of DNRM2. |
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| 63 | * |
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| 64 | END |
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