CFD Utilities Files

INTERP_1D DESCRIPTION:

   INTERP_1D provides for interactive interpolating/extrapolating
within a monotonic set of data points (at least two points).   In
particular,  it  answers the common case of interpolating a third
point from a given pair of points,  since  using  a calculator is
error-prone.

   Both linear and local cubic spline interpolation are  provided
here, possibly for comparison purposes.  64-bit arithmetic may be
advisable (as for careful capture of the end of a trajectory).

   Also calculated are the straight line slope and intercept  for
the appropriate interval in the table,  along with the derivative
from the spline fit.

METHOD:

   After the data file  ("table")  and spline method are entered,
the inner loop over abscissas of interest prompts for each target
abscissa and displays the interpolated (or extrapolated) results.

DATA FORMAT:

   (X, Y) data in two columns, read until EOF.

PROCEDURES:

   TABLE1    Linear interpolation table look-up utility which
             returns the relevant interval - otherwise, we could
             use the linear option in LCSFIT.
   LCSFIT    Local cubic spline utility (4-point method).

HISTORY:

   DAS   10/21/83   Test program for TABLE1.
   DAS   08/08/86   Slight clean up as INTERP1D.
   DAS   04/07/87   More tidy up for publication.
 DAS/RAK 03/04/88   Slope and intercept displayed now.
   DAS   05/23/02   INTERP_1D version intended for higher precision
                    data, prompted by Traj_opt gradient difficulties.
                    Read the data from a file instead of prompting,
                    but prompt for target abscissas.  See SMOOTH
                    for much more complete handling of (X, Y) data.

AUTHOR:  David Saunders, ELORET/NASA Ames Research Center.