Subject:
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Re: Quick way to mirror-image a model?
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Newsgroups:
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lugnet.cad
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Date:
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Wed, 23 Jun 2004 16:36:30 GMT
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Viewed:
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3983 times
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In lugnet.cad, Don Heyse wrote:
> Matrix multiplication is not commutative. (distributive? Err, I
> forget my math terms.) You're doing one or more of the multiplications
> in the wrong order?
It's neither commutative [(a * b) * c != a * (b * c)] nor associative [a * b !=
b * a].
That shouldn't be the problem in the calculation above, since the current matrix
was the identity matrix...
> Try ME * (MC * MP) instead. Notice I switched the order inside the
> parens, and outside.
> Check how I do it in my code. You'll probably have to fetch L3Math.c
> and L3Def.h from the ldglite CVS archive on the sourceforge to see
> the order, because I think I only put the new stuff in the mirwiz.zip
> file.
Looks like you're doing MF = MP * (MC * ME) in the code?
Thanks,
Carl
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Message has 1 Reply:
 | | Re: Quick way to mirror-image a model?
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| (...) Yes, that looks right. The other thing that messes me up with LDRAW matrices is the row, column ordering. The ordering in LDRAW files is not what I would have chosen, so I always have to look it up. From the old FAQ: (URL) type 1's format is: (...) (20 years ago, 23-Jun-04, to lugnet.cad, lugnet.cad.mlcad)
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Message is in Reply To:
| | Re: Quick way to mirror-image a model?
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| (...) Probably. ;^) (...) Matrix multiplication is not commutative. (distributive? Err, I forget my math terms.) You're doing one or more of the multiplications in the wrong order? Try ME * (MC * MP) instead. Notice I switched the order inside the (...) (20 years ago, 23-Jun-04, to lugnet.cad)
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