root / src / blas / snrm2.f @ 4
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| 1 | 1 | pfleura2 | REAL FUNCTION SNRM2(N,X,INCX) |
|---|---|---|---|
| 2 | 1 | pfleura2 | * .. Scalar Arguments .. |
| 3 | 1 | pfleura2 | INTEGER INCX,N |
| 4 | 1 | pfleura2 | * .. |
| 5 | 1 | pfleura2 | * .. Array Arguments .. |
| 6 | 1 | pfleura2 | REAL X(*) |
| 7 | 1 | pfleura2 | * .. |
| 8 | 1 | pfleura2 | * |
| 9 | 1 | pfleura2 | * Purpose |
| 10 | 1 | pfleura2 | * ======= |
| 11 | 1 | pfleura2 | * |
| 12 | 1 | pfleura2 | * SNRM2 returns the euclidean norm of a vector via the function |
| 13 | 1 | pfleura2 | * name, so that |
| 14 | 1 | pfleura2 | * |
| 15 | 1 | pfleura2 | * SNRM2 := sqrt( x'*x ). |
| 16 | 1 | pfleura2 | * |
| 17 | 1 | pfleura2 | * Further Details |
| 18 | 1 | pfleura2 | * =============== |
| 19 | 1 | pfleura2 | * |
| 20 | 1 | pfleura2 | * -- This version written on 25-October-1982. |
| 21 | 1 | pfleura2 | * Modified on 14-October-1993 to inline the call to SLASSQ. |
| 22 | 1 | pfleura2 | * Sven Hammarling, Nag Ltd. |
| 23 | 1 | pfleura2 | * |
| 24 | 1 | pfleura2 | * |
| 25 | 1 | pfleura2 | * .. Parameters .. |
| 26 | 1 | pfleura2 | REAL ONE,ZERO |
| 27 | 1 | pfleura2 | PARAMETER (ONE=1.0E+0,ZERO=0.0E+0) |
| 28 | 1 | pfleura2 | * .. |
| 29 | 1 | pfleura2 | * .. Local Scalars .. |
| 30 | 1 | pfleura2 | REAL ABSXI,NORM,SCALE,SSQ |
| 31 | 1 | pfleura2 | INTEGER IX |
| 32 | 1 | pfleura2 | * .. |
| 33 | 1 | pfleura2 | * .. Intrinsic Functions .. |
| 34 | 1 | pfleura2 | INTRINSIC ABS,SQRT |
| 35 | 1 | pfleura2 | * .. |
| 36 | 1 | pfleura2 | IF (N.LT.1 .OR. INCX.LT.1) THEN |
| 37 | 1 | pfleura2 | NORM = ZERO |
| 38 | 1 | pfleura2 | ELSE IF (N.EQ.1) THEN |
| 39 | 1 | pfleura2 | NORM = ABS(X(1)) |
| 40 | 1 | pfleura2 | ELSE |
| 41 | 1 | pfleura2 | SCALE = ZERO |
| 42 | 1 | pfleura2 | SSQ = ONE |
| 43 | 1 | pfleura2 | * The following loop is equivalent to this call to the LAPACK |
| 44 | 1 | pfleura2 | * auxiliary routine: |
| 45 | 1 | pfleura2 | * CALL SLASSQ( N, X, INCX, SCALE, SSQ ) |
| 46 | 1 | pfleura2 | * |
| 47 | 1 | pfleura2 | DO 10 IX = 1,1 + (N-1)*INCX,INCX |
| 48 | 1 | pfleura2 | IF (X(IX).NE.ZERO) THEN |
| 49 | 1 | pfleura2 | ABSXI = ABS(X(IX)) |
| 50 | 1 | pfleura2 | IF (SCALE.LT.ABSXI) THEN |
| 51 | 1 | pfleura2 | SSQ = ONE + SSQ* (SCALE/ABSXI)**2 |
| 52 | 1 | pfleura2 | SCALE = ABSXI |
| 53 | 1 | pfleura2 | ELSE |
| 54 | 1 | pfleura2 | SSQ = SSQ + (ABSXI/SCALE)**2 |
| 55 | 1 | pfleura2 | END IF |
| 56 | 1 | pfleura2 | END IF |
| 57 | 1 | pfleura2 | 10 CONTINUE |
| 58 | 1 | pfleura2 | NORM = SCALE*SQRT(SSQ) |
| 59 | 1 | pfleura2 | END IF |
| 60 | 1 | pfleura2 | * |
| 61 | 1 | pfleura2 | SNRM2 = NORM |
| 62 | 1 | pfleura2 | RETURN |
| 63 | 1 | pfleura2 | * |
| 64 | 1 | pfleura2 | * End of SNRM2. |
| 65 | 1 | pfleura2 | * |
| 66 | 1 | pfleura2 | END |