From octave-sources-request at bevo dot che dot wisc dot edu  Wed Jul 19 18:25:40 2000
Subject: Re: Errorbar update
From: pkienzle at kienzle dot powernet dot co dot uk (Paul Kienzle)
To: tpikonen at pcu dot helsinki dot fi
Cc: octave-sources at bevo dot che dot wisc dot edu
Date: Wed, 19 Jul 2000 23:34:25 +0100 (BST)

Teemu,

	Thanks for coding the errorbar() function.  I've had a chance
to try it out, and found a few issues:

1) Matlab's doc:
	errorbar(X,Y,L,U) plots X versus Y with error bars L(i)+U(i) long
	specifying the lower and upper error bars. X, Y, L, and U must be
	the same size. When they are vectors, each error bar is a distance
	of L(i) below and U(i) above the point defined by (X(i),Y(i)).
	When they are matrices, each error bar is a distance of L(i,j)
	below and U(i,j) above the point defined by (X(i,j),Y(i,j)).

   Your implementation seems to to want errorbar(x,y,y-l,y+u) instead
   of errorbar(x,y,l,u).

2) Matlab's doc:
	errorbar(...,LineSpec) draws the error bars using the line type,
	marker symbol, and color specified by LineSpec.

   In particular, Matlab's errorbar(x,y) does the default linespec for
   plot, which is to draw a line connecting the points, but can be set
   to any sort of linespec between the points.  Gnuplot can only do one
   thing at a time (errorbar or line), so you will have to do a plot,
   hold, plot with "w <blah>" -> "w e" and "t <blah>" -> "notitle".  Could 
   be tricky.

   Particularly confusing is:
	errorbar(x,y,dy,";;");
   which not only supresses the legend entry, but also supresses the
   error bars themselves, drawing instead a line to connect the x-y's.

3) I'm not sure what the point of "#" style is.  bar(x,y) seems to
   do what you need, except it doesn't handle overlapping boxes.  I can
   understand the need for "#~" (confidence levels on your bar charts),
   but for the few times that you need them, you can do that with:
	bar(x,y); hold on; errorbar(x,y,dy,".;;"); hold off;

4) The plot options ~, < and # don't work with the plot() command
   (obviously),  which makes an already confusing command even more
   confusing.  Couldn't you have three different commands for error bars:
	errorbar(), xerrorbar(), xyerrorbar()
   This takes care of ~ and <, and you can drop the # option entirely
   since it is more or less handled by bar().

5) Even the matrix version works. Wow!  A minor problem though:
	octave:179> errorbar([x x], [y y+2], [dy dy], ["~;y;" ; "~;y+2;"])
	error: invalid conversion from string to real matrix
	error: evaluating index expression near line 76, column 15
	error: evaluating assignment expression near line 76, column 13
	error: evaluating for command near line 69, column 5
	error: evaluating if command near line 62, column 1
	error: called from `__errplot' in file ...
	error: called from `errorbar' in file ...

Paul Kienzle
pkienzle at kienzle dot powernet dot co dot uk



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