# -*- coding: utf-8 -*-
"""
Created on Fri May 17 17:11:14 2019

@author: 
"""
import math

"""
*> \brief \b DDOT
*
*  =========== DOCUMENTATION ===========
*
* Online html documentation available at
*            http://www.netlib.org/lapack/explore-html/
*
*  Definition:
*  ===========
*
*       DOUBLE PRECISION FUNCTION DDOT(N,DX,INCX,DY,INCY)
*
*       .. Scalar Arguments ..
*       INTEGER INCX,INCY,N
*       ..
*       .. Array Arguments ..
*       DOUBLE PRECISION DX(*),DY(*)
*       ..
*
*
*> \par Purpose:
*  =============
*>
*> \verbatim
*>
*>    DDOT forms the dot product of two vectors.
*>    uses unrolled loops for increments equal to one.
*> \endverbatim
*
*  Arguments:
*  ==========
*
*> \param[in] N
*> \verbatim
*>          N is INTEGER
*>         number of elements in input vector(s)
*> \endverbatim
*>
*> \param[in] DX
*> \verbatim
*>          DX is DOUBLE PRECISION array, dimension ( 1 + ( N - 1
*)*abs( INCX ) )
*> \endverbatim
*>
*> \param[in] INCX
*> \verbatim
*>          INCX is INTEGER
*>         storage spacing between elements of DX
*> \endverbatim
*>
*> \param[in] DY
*> \verbatim
*>          DY is DOUBLE PRECISION array, dimension ( 1 + ( N - 1
*)*abs( INCY ) )
*> \endverbatim
*>
*> \param[in] INCY
*> \verbatim
*>          INCY is INTEGER
*>         storage spacing between elements of DY
*> \endverbatim
*
*  Authors:
*  ========
*
*> \author Univ. of Tennessee
*> \author Univ. of California Berkeley
*> \author Univ. of Colorado Denver
*> \author NAG Ltd.
*
*> \date November 2017
*
*> \ingroup double_blas_level1
*
*> \par Further Details:
*  =====================
*>
*> \verbatim
*>
*>     jack dongarra, linpack, 3/11/78.
*>     modified 12/3/93, array(1) declarations changed to array(*)
*> \endverbatim
*>
*  =====================================================================
"""
#DOUBLE PRECISION FUNCTION ddot(N,DX,INCX,DY,INCY)
def ddot(n, dx, incx, dy, incy):
    
    #*
    #*  -- Reference BLAS level1 routine (version 3.8.0) --
    #*  -- Reference BLAS is a software package provided by Univ. of
    #*  Tennessee,    --
    #*  -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG
    #*  Ltd..--
    #*     November 2017
    #*
    #*     .. Scalar Arguments ..
    #INTEGER INCX,INCY,N
    #*     ..
    #*     .. Array Arguments ..
    #DOUBLE PRECISION DX(*),DY(*)
    #*     ..
    #*
    #*  =====================================================================
    #*
    #*     .. Local Scalars ..
    dtemp = 0.0e0
    i = 0
    ix = 0
    iy = 0
    m = 0
    mp1 = 0
    
    #DOUBLE PRECISION DTEMP
    #INTEGER I,IX,IY,M,MP1
    #*     ..
    #*     .. Intrinsic Functions ..
    #INTRINSIC mod
    #*     ..
    #ddot = 0.0d0
    returnValue = 0.0e0
    dtemp = 0.0e0
    
    #IF (n.LE.0) RETURN
    if (n > 0):
        
        #IF (incx.EQ.1 .AND. incy.EQ.1) THEN
        if (incx == 1 and incy == 1):
            #*
            #*        code for both increments equal to 1
            #*
            #*
            #*        clean-up loop
            #*
            m = n % 5
            
            #IF (m.NE.0) THEN
            if (m != 0):
                
                #DO i = 1,m
                for i in range(m):
                    dtemp = dtemp + dx[i]*dy[i]
            
                #IF (n.LT.5) THEN
                if (n < 5):
                    
                    #ddot=dtemp
                    returnValue = dtemp
                    #RETURN
            
            if (n >= 5):
             
                mp1 = m + 1
             
                #DO i = mp1,n,5
                for i in range(mp1-1, n, 5):
                 
                    dtemp = dtemp + dx[i]*dy[i] + dx[i+1]*dy[i+1] +\
                    dx[i+2]*dy[i+2] + dx[i+3]*dy[i+3] + dx[i+4]*dy[i+4]
         
        else:
            #*
            #*        code for unequal increments or equal increments
            #*          not equal to 1
            #*
            #ix = 1
            #iy = 1
            ix = 0
            iy = 0       
            if (incx < 0):
                ix = ((-1*n)+1)*incx + 1
            if (incy < 0):
                iy = ((-1*n)+1)*incy + 1
            #DO i = 1,n
            for i in range(n):
                dtemp = dtemp + dx[ix]*dy[iy]
                ix = ix + incx
                iy = iy + incy


    #ddot = dtemp
    returnValue = dtemp
      
    return returnValue