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[37] | 1 | function Y = cosh(X) |
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| 2 | % COSH Hyperbolic cosine. |
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| 3 | % (Quaternion overloading of standard Matlab function.) |
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| 4 | |
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| 5 | % Copyright © 2006 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 | error(nargchk(1, 1, nargin)), error(nargoutchk(0, 1, nargout)) |
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| 9 | |
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| 10 | if isreal(X) |
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| 11 | |
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| 12 | % X is a real quaternion, and we compute the hyperbolic cosine of an |
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| 13 | % isomorphic complex number using the standard Matlab cosh function, |
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| 14 | % then construct a quaternion with the same axis as the original |
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| 15 | % quaternion. |
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| 16 | |
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| 17 | Y = isoquaternion(cosh(isocomplex(X)), X); |
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| 18 | else |
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| 19 | |
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| 20 | % X is a complex quaternion, and therefore we cannot use the method |
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| 21 | % above for real quaternions, because it is not possible to construct |
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| 22 | % an isomorphic complex number. We use instead a fundamental formula |
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| 23 | % for the hyperbolic cosine. |
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| 24 | |
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| 25 | Y = (exp(X) + exp(-X)) ./ 2; |
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| 26 | end; |
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