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What is the name given to numeric 4's whose top lines do not meet? February 15, 2009 ( talk) 02:05, 16 October 2008 (UTC)
I don't get this; where am I going wrong - it's a vector rotation thing:
aa = 10*pi/180; %angle of 10 degrees in radians
V1= [ 0, 0.342020143325670, 0.939692620785908]; % vector I'm interested in using
R_mat=[ cos(aa), 0, -sin(aa) ; 0 ,1, 0; sin(aa), 0, cos(aa) ]; % rotating by 10 degrees around y-axis
V3 = R_mat * V1'; % rotate V1 by 10 degrees
d = dot(V1,V3) / (norm(V1) * norm(V3)); % dot product
a = acos(d); % check angle between them
The answer I get should be 0.1745 (in format short), but I get 0.1640.
To summarise: I have the particular result shown in V1 from an intermediate stage of a larger problem. I rotate it by 10 degrees using the matrix shown. Then, to verify, I use the dot product of the vectors to determine the angle between them.
What have I done wrong? I am not ashamed to be embarrassed at this stage! Fritzpoll ( talk) 10:01, 16 October 2008 (UTC)
The cross product of two vectors has the direction of the axis of rotation. But you want to extract the axis of rotation from the two vectors and the angle of rotation, right? Bo Jacoby ( talk) 11:25, 16 October 2008 (UTC).
Mathematics desk | ||
---|---|---|
< October 15 | << Sep | October | Nov >> | October 17 > |
Welcome to the Wikipedia Mathematics Reference Desk Archives |
---|
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages. |
What is the name given to numeric 4's whose top lines do not meet? February 15, 2009 ( talk) 02:05, 16 October 2008 (UTC)
I don't get this; where am I going wrong - it's a vector rotation thing:
aa = 10*pi/180; %angle of 10 degrees in radians
V1= [ 0, 0.342020143325670, 0.939692620785908]; % vector I'm interested in using
R_mat=[ cos(aa), 0, -sin(aa) ; 0 ,1, 0; sin(aa), 0, cos(aa) ]; % rotating by 10 degrees around y-axis
V3 = R_mat * V1'; % rotate V1 by 10 degrees
d = dot(V1,V3) / (norm(V1) * norm(V3)); % dot product
a = acos(d); % check angle between them
The answer I get should be 0.1745 (in format short), but I get 0.1640.
To summarise: I have the particular result shown in V1 from an intermediate stage of a larger problem. I rotate it by 10 degrees using the matrix shown. Then, to verify, I use the dot product of the vectors to determine the angle between them.
What have I done wrong? I am not ashamed to be embarrassed at this stage! Fritzpoll ( talk) 10:01, 16 October 2008 (UTC)
The cross product of two vectors has the direction of the axis of rotation. But you want to extract the axis of rotation from the two vectors and the angle of rotation, right? Bo Jacoby ( talk) 11:25, 16 October 2008 (UTC).