Heading:qjk40(635)
IDL DESIGN:  Design Extensionsy756qjk40
Page Numbers: Yes  X: 527  Y: 10.5" qjk40
XEROX Palo Alto Research Center						9 February 1977
Inter-Office Memorandumz18592y762\f2 5f5 1b25f0B6f5 15f0 1f5b
To	IDL Group	From	Beau Sheilz18592l4445d2998e18(0,65535)(1,4445)(2,14371)(3,13411)(4,15796)(5,11684)(6,14146)\2t2 1t0 9t4 1t0 4t5 1t0
File	<IDL>Design.Extensions	IDL Design Note Number:  3e12qjk40(2,11695)(4,65535)(5,65535)(6,65535)\27t4 1t0
Subject	 Extensions to the Harvard Designe12qjk40(635)\7t2 1t0
This document describes ways in which the new version of IDL might be extended beyond the design specified in the IDL Reference Manual.  No deep issues are involved - just matters of relatively straightforward addition or alteration.  Rough priorities are also suggested.e18j
The following are known weaknesses or omissions in the design expressed in the current manual which we might consider fixing.e12j
1.	Several classes of statistics are not covered adequately by the current set of functions.  These include l3552d2999j(0,65535)(1,3549)(2,65535)(3,65535)\2t2 1t0
a.	eigenvalue based statistics.  Some variant of the operators described in Dempster (1969) will probably be the basis of our approach to these.  [Dempster is on order for the Library]l4160d3563j(2,4160)\2t3 1t0
b.	repeated measure anova beyond the pre-test post-test case described in the manual.l4160d3563j\2t3 1t0
c.	iterative table fitting.l4160d3563j\2t3 1t0
d.	multidimensional scaling.l4160d3563j\2t3 1t0
e.	a primitive to derive pair oriented non-parametric statistics - such as GAMMA, TAU - from COUNT tables.l4160d3563j\2t3 1t0
These should be added whenever a treatment of them compatible with the IDL philosophy can be devised.  As this involves some relatively deep thought, I propose it be deferred for the time being.l3563j(2,65535)\106i4I
2.	The set of abilities provided by RESHAPE, REFORM, and ALLOC should be combined into one array generating function.  This routine should also take a string expression or a function as a specification of the contents of the array (like RECODE).  High priority.l3552d2999j\2t2 1t0
3.	An n-tile cut function (which returns an N-1 vector of values which divide its argument vector into N equifrequent intervals (medians, quartiles etc.)) should be added.  Moderate priority - sooner than (1) as is very straightforward.l3552d2999j\2t2 1t0
4.	A function to compute determinants would be a nice closure for the matrix functions.  Low priority - simple, but rarely used.l3552d2999j\2t2 1t0
5.	The compress functions should take forms, not integer weight codes, to do the weighting of observations.  (Some care in handling free variables must be exercised, and this is an important issue as other functions already in the system have this problem).  To be done when compression functions are redone - moderate priority.l3552d2999j\2t2 1t0 35i5I
6.	Random number generation was hacked in IDL-PPL to use the PPL random number generator.  A better solution, compatible with DEAL and other IDL ideas, is to have RANDOM(a) return a vector of length a of random reals between 0 and 1.  The function of setting the seed for the random number generator (used by both RANDOM and DEAL) should be split off into a separate function.  We may wish to add an analogous function that generates random normal deviates.l3552d2999j\2t2 455t0
j(635)