[37] | 1 | function b = subsref(a, ss) |
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| 2 | % SUBSREF Subscripted reference. |
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| 3 | % (Quaternion overloading of standard Matlab function.) |
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| 4 | |
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| 5 | % Copyright © 2005 Stephen J. Sangwine and Nicolas Le Bihan. |
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| 6 | % See the file : Copyright.m for further details. |
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| 7 | |
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| 8 | if length(ss) ~= 1 |
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| 9 | error('Only one level of subscripting is currently supported for quaternions.'); |
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| 10 | % See the notes below under structure indexing. |
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| 11 | end |
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| 12 | |
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| 13 | switch ss.type |
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| 14 | case '()' |
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| 15 | if length(ss) ~= 1 |
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| 16 | error('Multiple levels of subscripting are not supported for quaternions.') |
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| 17 | end |
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| 18 | |
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| 19 | % To implement indexing, we separate the quaternion into components, and then |
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| 20 | % compose the quaternion from the indexed components. |
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| 21 | |
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| 22 | if ispure(a) |
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| 23 | xa = x(a); ya = y(a); za = z(a); |
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| 24 | b = quaternion(xa(ss.subs{:}), ya(ss.subs{:}), za(ss.subs{:})); |
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| 25 | else |
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| 26 | sa = s(a); xa = x(a); ya = y(a); za = z(a); |
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| 27 | b = quaternion(sa(ss.subs{:}), xa(ss.subs{:}), ya(ss.subs{:}), za(ss.subs{:})); |
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| 28 | end |
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| 29 | case '{}' |
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| 30 | error('Cell array indexing is not valid for quaternions.') |
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| 31 | case '.' |
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| 32 | % Structure indexing. |
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| 33 | % |
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| 34 | % See some notes on this subject in the file subsasgn.m. Here, we would |
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| 35 | % have to support two levels of indexing, such as q.x(1,2) and q(1,2).x |
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| 36 | % which would give the same result. The Matlab help on subsref explains |
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| 37 | % how this would work. We could accept s, x, y, or z as field names and |
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| 38 | % return x(a) etc, but we would really need to pass a second level of |
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| 39 | % subscripting back to subsref recursively. The code below is an |
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| 40 | % interim step to support one level of structure indexing. |
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| 41 | % |
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| 42 | % 15-Sep-2005 Code contributed by T.A. Ell. |
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| 43 | % |
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| 44 | switch ss.subs |
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| 45 | case {'vector', 'v'} |
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| 46 | b = vector(a); % maybe private function access would be better? |
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| 47 | case {'scalar', 's'} |
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| 48 | b = scalar(a); |
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| 49 | case {'x', 'I'} |
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| 50 | b = x(a); |
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| 51 | case {'y', 'J'} |
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| 52 | b = y(a); |
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| 53 | case {'z', 'K'} |
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| 54 | b = z(a); |
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| 55 | case 'imag' |
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| 56 | b = imag(a); |
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| 57 | case {'real'} |
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| 58 | b = real(a); |
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| 59 | otherwise |
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| 60 | error( ['Structure ''.', ss.subs, ''' is not a valid index']); |
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| 61 | end |
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| 62 | otherwise |
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| 63 | error('subsref received an invalid subscripting type.') |
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| 64 | end |
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