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# New Lamothe book PG.247 math question

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I have posted this in here rather than the math because I felt it more likely someone would have his new book and be reading this area. My problem is regarding some of the symbols he uses in Figure 4.5 on page 247. Yes, he does make a list and explains what the symbols he will use mean a few pages before but then he uses some symbols not on the lists. What I want to know is what does, _ ~ _ P mean and - mean and also - mean and finally when you have - something like P - < r . cos0, r . sin0 > what do the <> mean? - Help appreciated. Paul

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I haven''t read the book (actually, I hate lamothe, he doesn''t describe anything in his books. When you go through your old books in a year or two and find his book there you''ll think what the hell did i learn from this. Actually, I''m only basing that on his dummies game programming book, maybe the others are better)

anyway...
~ as a math operator? If its being done on matrices then it means they are equivalent (or more likely row equivalent)
If that doesn''t mean anything to you you should go read up on some basic linear algebra. If its not being done on matrices then I don''t know what it means. In programming its usually a "not" operator of some kind.

As for < blah > these brackets are used by some people when representing vectors. The elements inside the brackets, delimited by commas, are the components of a vector. For geometry, 2D and 3D the order is always and respectively. For 4D stuff the order isn''t very standard and it depends on what you''re talking about. If its 3D homogenous coordinates the w coordinate is usually last, i.e. but if you''re referring to quaternions, it is usually written first as either or w + or something.

Anyway, yeah, < ... > are vectors

-out

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quote:
Original post by Sir_Spritely
What I want to know is what does,
_ ~ _
P mean and - mean and also - mean and finally when you have
-
something like P - < r . cos0, r . sin0 > what do the <> mean?
-
Help appreciated.

I think the tilde ''~` is being used for ''approximatley equal to''. He did say in the book that he had some trouble getting the editors to be able to properly represent certain symbols (I have no idea why). As far as the other you mentioned, it looks like part of a method used to convert polar coordinates into cartesian coordinates. r is the magnitude of the polar coordinate and theta is the angle. You get the x component of the cartesian coordinate by multiplying the magnitude by cos(theta) and the y coordinate by multiplying the magnitude by sin(theta). So P is a point, or vector enclosed in the <> to show that it''s an ordered pair.

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