From help-octave-request at che dot utexas dot edu  Mon Jan 16 19:56:44 1995
Subject: Indexing "1-vectors"
From: Ted dot Harding at nessie dot mcc dot ac dot uk (Ted Harding)
To: help-octave at che dot utexas dot edu
Date: Tue, 17 Jan 1995 01:55:21 +0100 (GMT)

Apologies if this has all been settled before.

Using Octave-1.0, I have written a function which works fine with
vector arguments. It includes lines like

        rhod( rhod<=-1 ) = 0.5*( rho0( rhod<=-1 ) - 1);

to modify those elements of a vector satisfying a condition,
namely " rhod(i) <= -1 ", with reference to another vector rho0.

So far so good, provided the variables are vectors with more than
one element. But I would also like this function to work if the
arguments (and therefore the variables like "rhod", "rho0") are 1x1
matrices (equivalent to scalars). However, in such a case when the
condtion is false, Octave says

        error: index invalid or out of range for scalar type

and there seems to be no way to prevent this. Yet, if Octave could
be forced to view the "scalar" as a vector of length 1 rather than as a scalar
proper, the indexing behaviour should also work in this case, according
to the rule which seems to apply for M-vectors, namely:-

        For M-vectors A, B, C
        A( boolean_fn(C) ) = B( boolean_fn(C) )

should carry out the assignment A(i)=B(i) for elements (i)
for which boolean_fn(C(i)) is true, and do nothing for all other (i).
This works even if there are no elements (i) for which the condition
is true.

The dimension does not have to be greater than one for this rule to
be workable. Is it possible to force this behaviour in Octave-1.0,
or do I have to write a special-case "if ... " section to cope with
the scalar case?

With thanks,
Ted.                                     (Ted dot Harding at nessie dot mcc dot ac dot uk)