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Index Page invort_c
Table of contents
Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries
#### Procedure
       invort_c ( Invert nearly orthogonal matrices )

       void invort_c ( ConstSpiceDouble   m  [3][3],
                       SpiceDouble        mit[3][3] )
#### Abstract
       Construct the inverse of a 3x3 matrix with orthogonal columns and
       non-zero column norms using a numerically stable algorithm. The
       rows of the output matrix are the columns of the input matrix
       divided by the length squared of the corresponding columns.
#### Required_Reading
       None.
#### Keywords
       MATRIX
#### Brief_I/O
       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       m          I   A 3x3 matrix.
       mit        O   m after transposition and scaling of rows.
#### Detailed_Input
       m           is a 3x3 matrix.
#### Detailed_Output
       mit         is the matrix obtained by transposing m and dividing
                   the rows by squares of their norms.
#### Parameters
       None.
#### Exceptions
       1)  If any of the columns of `m' have zero length, the error
           SPICE(ZEROLENGTHCOLUMN) is signaled by a routine in the call
           tree of this routine.

       2)  If any column is too short to allow computation of the
           reciprocal of its length without causing a floating point
           overflow, the error SPICE(COLUMNTOOSMALL) is signaled by a
           routine in the call tree of this routine.
#### Files
       None.
#### Particulars
       Suppose that m is the matrix

              .-                      -.
              |   A*u    B*v     C*w   |
              |      1      1       1  |
              |                        |
              |   A*u    B*v     C*w   |
              |      2      2       2  |
              |                        |
              |   A*u    B*v     C*w   |
              |      3      3       3  |
              `-                      -'

       where the vectors (u , u , u ),  (v , v , v ),  and (w , w , w )
                           1   2   3      1   2   3          1   2   3

       are unit vectors. This routine produces the matrix:

              .-                      -.
              |   a*u    a*u     a*u   |
              |      1      2       3  |
              |                        |
              |   b*v    b*v     b*v   |
              |      1      2       3  |
              |                        |
              |   c*w    c*w     c*w   |
              |      1      2       3  |
              `-                      -'

       where a = 1/A, b = 1/B, and c = 1/C.
#### Examples
       The numerical results shown for this example may differ across
       platforms. The results depend on the SPICE kernels used as
       input, the compiler and supporting libraries, and the machine
       specific arithmetic implementation.

       1) Given a double precision 3x3 matrix with mutually orthogonal
          rows of arbitrary length, compute its inverse. Check that the
          original matrix times the computed inverse produces the
          identity matrix.

          Example code begins here.

          /.
             Program invort_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {

             /.
             Local variables.
             ./
             SpiceDouble          imat   [3][3];
             SpiceDouble          mout   [3][3];

             SpiceInt             i;

             /.
             Define a matrix to invert.
             ./
             SpiceDouble          m      [3][3] = { {0.0, -1.0, 0.0},
                                                    {0.5,  0.0, 0.0},
                                                    {0.0,  0.0, 1.0} };

             printf( "Original Matrix:\n" );
             for ( i = 0; i < 3; i++ )
             {

                printf( "%16.7f %15.7f %15.7f\n", m[i][0], m[i][1], m[i][2] );

             }

             /.
             Invert the matrix, then output.
             ./
             invort_c ( m, mout );

             printf( " \n" );
             printf( "Inverse Matrix:\n" );
             for ( i = 0; i < 3; i++ )
             {

                printf( "%16.7f %15.7f %15.7f\n",
                        mout[i][0], mout[i][1], mout[i][2] );

             }

             /.
             Check the `m' times `mout' produces the identity matrix.
             ./
             mxm_c ( m, mout, imat );

             printf( " \n" );
             printf( "Original times inverse:\n" );
             for ( i = 0; i < 3; i++ )
             {

                printf( "%16.7f %15.7f %15.7f\n",
                        imat[i][0], imat[i][1], imat[i][2] );

             }

             return ( 0 );
          }

          When this program was executed on a Mac/Intel/cc/64-bit
          platform, the output was:

          Original Matrix:
                 0.0000000      -1.0000000       0.0000000
                 0.5000000       0.0000000       0.0000000
                 0.0000000       0.0000000       1.0000000

          Inverse Matrix:
                 0.0000000       2.0000000       0.0000000
                -1.0000000       0.0000000       0.0000000
                 0.0000000       0.0000000       1.0000000

          Original times inverse:
                 1.0000000       0.0000000       0.0000000
                 0.0000000       1.0000000       0.0000000
                 0.0000000       0.0000000       1.0000000
#### Restrictions
       None.
#### Literature_References
       None.
#### Author_and_Institution
       N.J. Bachman        (JPL)
       J. Diaz del Rio     (ODC Space)
       W.L. Taber          (JPL)
#### Version
       -CSPICE Version 1.0.1, 01-NOV-2021 (JDR)

           Edited the header to comply with NAIF standard. Fixed I/O type
           of argument "mit" in -Brief_I/O table. Extended -Abstract
           section.

           Added complete code example.

       -CSPICE Version 1.0.0, 02-JAN-2002 (WLT) (NJB)
#### Index_Entries
       Transpose a matrix and invert the lengths of the rows
       Invert a pseudo orthogonal matrix
#### Link to routine invort_c source file invort_c.c

    Fri Dec 31 18:41:08 2021