dznrm2.f.html

来自「famous linear algebra library (LAPACK) p」· HTML 代码 · 共 94 行

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<pre>
      DOUBLE PRECISION FUNCTION <a name="DZNRM2.1"></a><a href="dznrm2.f.html#DZNRM2.1">DZNRM2</a>(N,X,INCX)
<span class="comment">*</span><span class="comment">     .. Scalar Arguments ..
</span>      INTEGER INCX,N
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Array Arguments ..
</span>      DOUBLE COMPLEX X(*)
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Purpose
</span><span class="comment">*</span><span class="comment">  =======
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  <a name="DZNRM2.12"></a><a href="dznrm2.f.html#DZNRM2.1">DZNRM2</a> returns the euclidean norm of a vector via the function
</span><span class="comment">*</span><span class="comment">  name, so that
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     <a name="DZNRM2.15"></a><a href="dznrm2.f.html#DZNRM2.1">DZNRM2</a> := sqrt( conjg( x' )*x )
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  -- This version written on 25-October-1982.
</span><span class="comment">*</span><span class="comment">     Modified on 14-October-1993 to inline the call to <a name="ZLASSQ.19"></a><a href="zlassq.f.html#ZLASSQ.1">ZLASSQ</a>.
</span><span class="comment">*</span><span class="comment">     Sven Hammarling, Nag Ltd.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Parameters ..
</span>      DOUBLE PRECISION ONE,ZERO
      PARAMETER (ONE=1.0D+0,ZERO=0.0D+0)
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      DOUBLE PRECISION NORM,SCALE,SSQ,TEMP
      INTEGER IX
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC ABS,DBLE,DIMAG,SQRT
<span class="comment">*</span><span class="comment">     ..
</span>      IF (N.LT.1 .OR. INCX.LT.1) THEN
          NORM = ZERO
      ELSE
          SCALE = ZERO
          SSQ = ONE
<span class="comment">*</span><span class="comment">        The following loop is equivalent to this call to the LAPACK
</span><span class="comment">*</span><span class="comment">        auxiliary routine:
</span><span class="comment">*</span><span class="comment">        CALL <a name="ZLASSQ.41"></a><a href="zlassq.f.html#ZLASSQ.1">ZLASSQ</a>( N, X, INCX, SCALE, SSQ )
</span><span class="comment">*</span><span class="comment">
</span>          DO 10 IX = 1,1 + (N-1)*INCX,INCX
              IF (DBLE(X(IX)).NE.ZERO) THEN
                  TEMP = ABS(DBLE(X(IX)))
                  IF (SCALE.LT.TEMP) THEN
                      SSQ = ONE + SSQ* (SCALE/TEMP)**2
                      SCALE = TEMP
                  ELSE
                      SSQ = SSQ + (TEMP/SCALE)**2
                  END IF
              END IF
              IF (DIMAG(X(IX)).NE.ZERO) THEN
                  TEMP = ABS(DIMAG(X(IX)))
                  IF (SCALE.LT.TEMP) THEN
                      SSQ = ONE + SSQ* (SCALE/TEMP)**2
                      SCALE = TEMP
                  ELSE
                      SSQ = SSQ + (TEMP/SCALE)**2
                  END IF
              END IF
   10     CONTINUE
          NORM = SCALE*SQRT(SSQ)
      END IF
<span class="comment">*</span><span class="comment">
</span>      <a name="DZNRM2.66"></a><a href="dznrm2.f.html#DZNRM2.1">DZNRM2</a> = NORM
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="DZNRM2.69"></a><a href="dznrm2.f.html#DZNRM2.1">DZNRM2</a>.
</span><span class="comment">*</span><span class="comment">
</span>      END

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