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