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Indexing on row matrices
From: |
Daniel J Sebald |
Subject: |
Indexing on row matrices |
Date: |
Mon, 12 Aug 2013 02:32:05 -0500 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.24) Gecko/20111108 Fedora/3.1.16-1.fc14 Thunderbird/3.1.16 |
In working with assert.m and converting column vector indexed
matrices/vectors to strings I'm wondering if the following is correct:
a = [11 22]
a =
11 22
a ([1 2])
ans =
11 22
a ([1; 2])
ans =
11 22
I can easily work around this with
a ([1; 2]) (:)
ans =
11
22
but before doing so, I notice that the documentation isn't quite clear
on what the outcome should be:
"
8.1 Index Expressions
=====================
Vectors are indexed using a single index expression. Matrices (2-D)
and higher multi-dimensional arrays are indexed using either one index
or N indices where N is the dimension of the array. When using a
single index expression to index 2-D or higher data the elements of the
array are taken in column-first order (like Fortran).
The output from indexing assumes the dimensions of the index
expression. For example:
a(2) # result is a scalar
a(1:2) # result is a row vector
a([1; 2]) # result is a column vector
"
Now, the last result might lead one to believe that the above result for
a row vector is not correct. However, the discussion clearly has
drifted to the topic of matrices so the documentation neither confirms
or contradicts the output for indexing a row vector. If the result
above is correct, then it might be good to add that to the 8.1
documentation.
Dan
- Indexing on row matrices,
Daniel J Sebald <=