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Index Page ident_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
       ident_c ( Return the 3x3 identity matrix )

       void ident_c ( SpiceDouble    matrix[3][3] )
#### Abstract
       Return the 3x3 identity matrix.
#### Required_Reading
       None.
#### Keywords
       MATRIX
#### Brief_I/O
       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       matrix     O   The 3x3 identity matrix.
#### Detailed_Input
       None.
#### Detailed_Output
       matrix      is the 3x3 Identity matrix. That `matrix' is
                   the following

                      .-                 -.
                      |  1.0   0.0   0.0  |
                      |  0.0   1.0   0.0  |
                      |  0.0   0.0   1.0  |
                      `-                 -'
#### Parameters
       None.
#### Exceptions
       Error free.
#### Files
       None.
#### Particulars
       This is a utility routine for obtaining the 3x3 identity matrix
       so that you may avoid having to write the loop or assignments
       needed to get the matrix.
#### 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) Define a 3x3 matrix and compute its inverse using the CSPICE
          routine invert_c. Verify the accuracy of the computed inverse
          using the mathematical identity

                  -1
             m x m   - i = 0

          where `i' is the 3x3 identity matrix.

          Example code begins here.

          /.
             Program ident_ex1
          ./
          #include <stdio.h>
          #include "SpiceUsr.h"

          int main( )
          {

             /.
             Local variables.
             ./
             SpiceDouble          idmat  [3][3];
             SpiceDouble          imat   [3][3];
             SpiceDouble          mout   [3][3];
             SpiceDouble          mzero  [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.
             ./
             invert_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.
             ./
             ident_c ( idmat );
             mxm_c   ( m, mout, imat );

             vsubg_c ( (SpiceDouble *)imat, (SpiceDouble *)idmat,
                        9,                  (SpiceDouble *)mzero );

             printf( "\n" );
             printf( "Original times inverse minus identity:\n" );
             for ( i = 0; i < 3; i++ )
             {
                printf( "%16.7f %15.7f %15.7f\n",
                        mzero[i][0], mzero[i][1], mzero[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 minus identity:
                 0.0000000       0.0000000       0.0000000
                 0.0000000       0.0000000       0.0000000
                 0.0000000       0.0000000       0.0000000
#### 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, 02-JUN-2021 (JDR)

           Edited the header to comply with NAIF standard. Added complete
           code example.

       -CSPICE Version 1.0.0, 01-JUN-1999 (NJB) (WLT)
#### Index_Entries
       Get the 3x3 identity matrix
#### Link to routine ident_c source file ident_c.c

    Fri Dec 31 18:41:08 2021