SNRM2/DNRM2/SCNRM2/DZNRM2 |
| Euclidean norm | ||
| INTEGER*8 | n, incx |
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| REAL*8 | s, DZNRM2 | ||
| COMPLEX*16 | x(lenx) |
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| s = DZNRM2(n, x, incx) |
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Input | n |
| Number of elements of vector x to be used in the | |
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| Euclidean norm. If n ≤ 0, the subprograms do not | |
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| reference x. | |
| x |
| Array of length lenx = (n−1)⋅incx+1 containing the | |
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| incx |
| Increment for the array x. x is stored forward in array x | |
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| with increment incx; that is, xi is stored in | |
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| x((i−1)⋅incx+1). | |
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| Use incx = 1 if the vector x is stored contiguously in | |
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| array x; that is, if xi is stored in x(i). Refer to “BLAS | |
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| Indexing Conventions” in the introduction to this | |
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| chapter. |
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Output | s |
| If n ≤ 0, then s = 0. Otherwise, s is the Euclidean norm | |
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| of x. |
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Fortran |
| REAL*4 FUNCTION SNRM2 ( N, X,INCX ) | ||
Equivalent |
| INTEGER*4 INCX, INCXA, IX, N | ||
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| REAL*4 ABSXI, SCALE, SSQ, X(*) | ||
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| IF ( N .GT. 1 ) THEN | ||
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| INCXA = ABS ( INCX ) | ||
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| SCALE | = 0.0 |
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| SSQ | = 1.0 |
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| DO 10 IX = 1, 1 + | ||
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| IF ( X(IX) .NE.0.0 ) THEN | ||
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| ABSXI = ABS ( X(IX) ) | |
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| IF ( SCALE .LT. ABSXI ) THEN | |
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| SSQ | = 1.0 + SSQ * (SCALE/ABSXI) ** 2 |
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| SCALE = ABSXI | |
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| ELSE |
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| SSQ | = SSQ + (ABSXI/SCALE) ** 2 |
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| END IF |
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| END IF |
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| 10 | CONTINUE |
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SNRM2 = SCALE | * SQRT ( SSQ ) |
ELSE IF ( N .EQ. | 1 ) THEN |
SNRM2 = ABS ( | X(1) ) |
ELSE |
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SNRM2 = 0.0 |
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END IF |
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RETURN |
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END |
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108HP MLIB User’s Guide