text: /*
  
  -Procedure      vlcom_c ( Vector linear combination, 3 dimensions )
  
  -Abstract
   
     Compute a vector linear combination of two double precision, 
     3-dimensional vectors. 
   
  -Disclaimer
  
     THIS SOFTWARE AND ANY RELATED MATERIALS WERE CREATED BY THE
     CALIFORNIA INSTITUTE OF TECHNOLOGY (CALTECH) UNDER A U.S.
     GOVERNMENT CONTRACT WITH THE NATIONAL AERONAUTICS AND SPACE
     ADMINISTRATION (NASA). THE SOFTWARE IS TECHNOLOGY AND SOFTWARE
     PUBLICLY AVAILABLE UNDER U.S. EXPORT LAWS AND IS PROVIDED "AS-IS"
     TO THE RECIPIENT WITHOUT WARRANTY OF ANY KIND, INCLUDING ANY
     WARRANTIES OF PERFORMANCE OR MERCHANTABILITY OR FITNESS FOR A
     PARTICULAR USE OR PURPOSE (AS SET FORTH IN UNITED STATES UCC
     SECTIONS 2312-2313) OR FOR ANY PURPOSE WHATSOEVER, FOR THE
     SOFTWARE AND RELATED MATERIALS, HOWEVER USED.
  
     IN NO EVENT SHALL CALTECH, ITS JET PROPULSION LABORATORY, OR NASA
     BE LIABLE FOR ANY DAMAGES AND/OR COSTS, INCLUDING, BUT NOT
     LIMITED TO, INCIDENTAL OR CONSEQUENTIAL DAMAGES OF ANY KIND,
     INCLUDING ECONOMIC DAMAGE OR INJURY TO PROPERTY AND LOST PROFITS,
     REGARDLESS OF WHETHER CALTECH, JPL, OR NASA BE ADVISED, HAVE
     REASON TO KNOW, OR, IN FACT, SHALL KNOW OF THE POSSIBILITY.
  
     RECIPIENT BEARS ALL RISK RELATING TO QUALITY AND PERFORMANCE OF
     THE SOFTWARE AND ANY RELATED MATERIALS, AND AGREES TO INDEMNIFY
     CALTECH AND NASA FOR ALL THIRD-PARTY CLAIMS RESULTING FROM THE
     ACTIONS OF RECIPIENT IN THE USE OF THE SOFTWARE.
  
  -Required_Reading
   
     None. 
   
  -Keywords
   
     VECTOR 
   
  */
  
     #include "SpiceUsr.h"
     #undef    vlcom_c
  
  
     void vlcom_c ( SpiceDouble        a, 
                    ConstSpiceDouble   v1[3], 
                    SpiceDouble        b, 
                    ConstSpiceDouble   v2[3], 
                    SpiceDouble        sum[3] ) 
  /*
  
  -Brief_I/O
   
     VARIABLE  I/O  DESCRIPTION 
     --------  ---  -------------------------------------------------- 
     a          I   Coefficient of v1 
     v1         I   Vector in 3-space 
     b          I   Coefficient of v2 
     v2         I   Vector in 3-space 
     sum        O   Linear Vector Combination a*v1 + b*v2 
   
  -Detailed_Input
   
     a     This double precision variable multiplies v1. 
     v1    This is an arbitrary, double precision 3-dimensional 
            vector. 
     b     This double precision variable multiplies v2. 
     v2    This is an arbitrary, double precision 3-dimensional 
            vector. 
   
  -Detailed_Output
   
     sum   is an arbitrary, double precision 3-dimensional vector 
            which contains the linear combination a*v1 + b*v2. 
   
  -Parameters
   
     None. 
   
  -Particulars
   
     For each index from 0 to 2, this routine implements in C 
     code the expression: 
   
     sum[i] = a*v1[i] + b*v2[i] 
   
     No error checking is performed to guard against numeric overflow. 
   
  -Examples
   
     To generate a sequence of points on an ellipse with major 
     and minor axis vectors major and minor, one could use the 
     following code fragment 
   
            step = twopi_c()/ n; 
            ang  = 0.0;
  
            for ( i = 0; i < n; i++ )
               { 
               vlcom_c ( cos(ang),major,  sin(ang),minor,  point );
   
               do something with the ellipse point just constructed 
  
               ang = ang + step;
               }
   
     As a second example, suppose that u and v are orthonormal vectors 
     that form a basis of a plane. Moreover suppose that we wish to 
     project a vector x onto this plane, we could use the following 
     call inserts this projection into proj. 
   
            vlcom_c ( vdot_c(x,v),v,   vdot_c(x,u),u,    proj ) 
   
   
  -Restrictions
   
     No error checking is performed to guard against numeric overflow 
     or underflow.  The user is responsible for insuring that the 
     input values are reasonable. 
   
  -Exceptions
   
     Error free. 
   
  -Files
   
     None 
   
  -Author_and_Institution
   
     W.L. Taber      (JPL) 
     E.D. Wright     (JPL)
   
  -Literature_References
   
     None 
   
  -Version
   
     -CSPICE Version 1.1.0, 22-OCT-1998 (NJB)
  
        Made input vectors const.
  
     -CSPICE Version 1.0.0, 08-FEB-1998 (EDW)
  
  -Index_Entries
   
     linear combination of two 3-dimensional vectors 
   
  -&
  */
  
  { /* Begin vlcom_c */
  
     /* This really doesn't require a degree in rocket science */
   
     sum[0] = a*v1[0] + b*v2[0];
     sum[1] = a*v1[1] + b*v2[1];
     sum[2] = a*v1[2] + b*v2[2];
  
  
  } /* End vlcom_c */
  