izmax1.f.html

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<pre>
      INTEGER          FUNCTION <a name="IZMAX1.1"></a><a href="izmax1.f.html#IZMAX1.1">IZMAX1</a>( N, CX, INCX )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  -- LAPACK auxiliary routine (version 3.1) --
</span><span class="comment">*</span><span class="comment">     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
</span><span class="comment">*</span><span class="comment">     November 2006
</span><span class="comment">*</span><span class="comment">
</span><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>      COMPLEX*16         CX( * )
<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="IZMAX1.17"></a><a href="izmax1.f.html#IZMAX1.1">IZMAX1</a> finds the index of the element whose real part has maximum
</span><span class="comment">*</span><span class="comment">  absolute value.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Based on IZAMAX from Level 1 BLAS.
</span><span class="comment">*</span><span class="comment">  The change is to use the 'genuine' absolute value.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Contributed by Nick Higham for use with <a name="ZLACON.23"></a><a href="zlacon.f.html#ZLACON.1">ZLACON</a>.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Arguments
</span><span class="comment">*</span><span class="comment">  =========
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  N       (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The number of elements in the vector CX.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  CX      (input) COMPLEX*16 array, dimension (N)
</span><span class="comment">*</span><span class="comment">          The vector whose elements will be summed.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  INCX    (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The spacing between successive values of CX.  INCX &gt;= 1.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment"> =====================================================================
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      INTEGER            I, IX
      DOUBLE PRECISION   SMAX
      COMPLEX*16         ZDUM
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC          ABS
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Statement Functions ..
</span>      DOUBLE PRECISION   CABS1
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Statement Function definitions ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     NEXT LINE IS THE ONLY MODIFICATION.
</span>      CABS1( ZDUM ) = ABS( ZDUM )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Executable Statements ..
</span><span class="comment">*</span><span class="comment">
</span>      <a name="IZMAX1.57"></a><a href="izmax1.f.html#IZMAX1.1">IZMAX1</a> = 0
      IF( N.LT.1 )
     $   RETURN
      <a name="IZMAX1.60"></a><a href="izmax1.f.html#IZMAX1.1">IZMAX1</a> = 1
      IF( N.EQ.1 )
     $   RETURN
      IF( INCX.EQ.1 )
     $   GO TO 30
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     CODE FOR INCREMENT NOT EQUAL TO 1
</span><span class="comment">*</span><span class="comment">
</span>      IX = 1
      SMAX = CABS1( CX( 1 ) )
      IX = IX + INCX
      DO 20 I = 2, N
         IF( CABS1( CX( IX ) ).LE.SMAX )
     $      GO TO 10
         <a name="IZMAX1.74"></a><a href="izmax1.f.html#IZMAX1.1">IZMAX1</a> = I
         SMAX = CABS1( CX( IX ) )
   10    CONTINUE
         IX = IX + INCX
   20 CONTINUE
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     CODE FOR INCREMENT EQUAL TO 1
</span><span class="comment">*</span><span class="comment">
</span>   30 CONTINUE
      SMAX = CABS1( CX( 1 ) )
      DO 40 I = 2, N
         IF( CABS1( CX( I ) ).LE.SMAX )
     $      GO TO 40
         <a name="IZMAX1.88"></a><a href="izmax1.f.html#IZMAX1.1">IZMAX1</a> = I
         SMAX = CABS1( CX( I ) )
   40 CONTINUE
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="IZMAX1.93"></a><a href="izmax1.f.html#IZMAX1.1">IZMAX1</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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