Training speed of Regression Forest about randomforest-matlab HOT 1 OPEN

Hi Kang

yeh there is a difference between the regression/classification code. when 
creating tree you need to split data but before splitting you need to sort data 
falling into a node. the classification code uses a pre-sorted array and that 
makes the classification code scale as O(number of example) whereas regression 
code uses on the fly code and that makes regression code scale as O(nlog(n)) - 
best sort code scaling.

i am guessing you have lots of examples and thats one reason regression might 
be slower. 

the other reason might be that regression trees may be split totally (i.e leaf 
nodes have the minimum number of examples) whereas your classification trees 
might be much simpler (a low VC dimension)

calculate the mean number of nodes in the model created, that might give you 
some more idea
mean(modelRf.ndbigtree) (classification)
mean(modelRf.ndtree)(regression)