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1 | function y = axis(x) |
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2 | % AXIS Axis of quaternion. |
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3 | % If Q = A + mu .* B where A and B are real/complex, and mu is a unit pure |
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4 | % quaternion, then axis(Q) = mu. |
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5 | |
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6 | % Copyright © 2005 Stephen J. Sangwine and Nicolas Le Bihan. |
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7 | % See the file : Copyright.m for further details. |
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8 | |
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9 | error(nargchk(1, 1, nargin)), error(nargoutchk(0, 1, nargout)) |
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10 | |
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11 | % In the warning check that follows, abs is used twice in order to handle |
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12 | % complexified quaternions with a complex modulus. |
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13 | |
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14 | if any(abs(abs(v(x))) < eps) |
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15 | warning('At least one element may have an undefined axis.'); |
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16 | end |
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17 | |
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18 | % Make a unit version of x before taking the vector part. This is essential |
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19 | % in the case where x is a complex quaternion, but has no effect when x is |
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20 | % a real quaternion. SJS 20 September 2005. |
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21 | |
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22 | y = unit(v(unit(x))); |
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