[chronojump] Fixed problem with extrema cross that sometimes did not find 0 cross

[Xavier de Blas <xaviblas src gnome org>]

commit 2732a95c8846b106ed8fc5535511d94c7fcb6546
Author: Xavier de Blas <xaviblas gmail com>
Date:   Mon May 18 21:01:55 2015 +0200

    Fixed problem with extrema cross that sometimes did not find 0 cross

 encoder/util.R |   29 ++++++++++++++++++++++++++++-
 1 files changed, 28 insertions(+), 1 deletions(-)
---
diff --git a/encoder/util.R b/encoder/util.R
index c496b48..2ceb127 100644
--- a/encoder/util.R
+++ b/encoder/util.R
@@ -146,7 +146,34 @@ extrema <- function(y, ndata = length(y), ndatam1 = ndata - 1) {
                        }
                        ncross <- nrow(cross)        
                }
-       } 
+       }
+
+       #extrema cross working:
+       #a=c(-3,-2,-1,0,1,2,1)
+       #extrema(a)$cross
+       #     [,1] [,2]
+       #[1,]    4    4
+       #extrema(a)$ncross
+       #[1] 1
+       #
+       #But, if there's no change of direction, cross does not find anything:
+       #a=c(-3,-2,-1,0,1,2)
+       #extrema(a)$cross
+       #NULL
+       #extrema(a)$ncross
+       #[1] 0
+       #
+       #then find a cross in this situation. Find just one cross.
+       if(ncross == 0) {
+               positiveAtStart = (y[1] >= 0)
+               for(i in 1:length(y)) {
+                       if( (y[i] >= 0) != positiveAtStart) { #if there's a sign change
+                               cross = rbind(cross, c(i-1,i))
+                               ncross = 1
+                               break
+                       }
+               }
+       }
 
        list(minindex=minindex, maxindex=maxindex, nextreme=nextreme, cross=cross, ncross=ncross)
 }