This directory contains grating descriptions.

PARAMETERS:

    The following grating parameters are used.

          title - Title used for labeling of output.
    description - Multiple lines of text used for documentation of output.
     tablescale - Factor by which to multiply the table values.
 	   type - Type of disperser: grating.
	    gmm - Grooves per mm.
	  blaze - Blaze angle in degrees.
    reflectance - Fractional reflectance of grating.

TABLE:

    The grating table has three columns, the first order wavelength in
    Angstroms, the order, and the fractional efficiency at that
    wavelength.  For values in percent use a "tablescale" parameter of
    0.01.  If no table is given the efficiency (blaze function) is
    calculated.  Normally the calculated function is used since the grating
    may be used in a wide range of configurations.  However if the grating
    is used in a limit set of configurations (same spectrograph and a few
    orders) a table may be appropriate.

    Note that the wavelengths are always at first order so that the table
    may be given in the required regular form.  So for multiple orders the
    sample points are at the same first order values (wavelength * order)
    though the efficiency values will be for the particular order.

EXAMPLE

    # title = "BL 181: 316 l/mm
    # type = grating
    # gmm = 316 groves/mm
    # blaze = 7.396 deg
    # reflectance = 0.78

SYNTAX:

    Comment lines begin with '#' and can contain any text and can occur
    anywhere in the file, though normally found at the beginning.

    Parameters are comment lines with the form

	# <parameter> = <value>

    where whitespace is required between each field, <parameter> is a single
    word parameter name, and <value> is a single word value.  A quoted string
    is a single word so if the value contains whitespace it must be quoted.
    Any text following the value is ignored.

    The optional table is a multicolumn list of numeric values.  The list
    must be in increasing order in the independent columns.  Only 1D (two
    columns) and 2D (three columns) tables are currently supported.  2D
    tables must form a regular grid.  The table will be interpolated.
    Extrapolation outside of the table consists of the taking the nearest
    value; thus, a single line defines a constant value for all values of
    the independent variable.  If a "tablescale" parameter is specified
    then the table values are multiplied by this value.
