Index expressions, boolean types and numerical types

[Greg Novak]

Does Octave have boolean types?  Does it keep track of them silently?  How 
do you do casts between numerical types and boolean types?  If there are 
no boolean types, then how does the following fragment of a session make 
sense?

octave:68> y=1:10
y = 1   2   3   4   5   6   7   8   9  10
octave:69> y(y<11)
ans = 1   2   3   4   5   6   7   8   9  10
octave:70> k=y<11
k = 1  1  1  1  1  1  1  1  1  1
octave:71> y(k)
ans = 1   2   3   4   5   6   7   8   9  10
octave:72> k=ones(1,10)
k = 1  1  1  1  1  1  1  1  1  1 
octave:73> y(k)
ans = 1  1  1  1  1  1  1  1  1  1 
octave:74>

k looks exactly the same when I assign it by k=y<11 or k=ones(1,10), but 
the behavior of y(k) is very different in the two cases.

What gives?
Thanks,
Greg



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