Re: Vector Question

From: Sean (TeamHubbell_at_charter.net)
Date: 06/21/04 

Date: 21 Jun 2004 15:35:54 -0700

Lynn Kurtz <kurtzDELETE-THIS@asu.edu> wrote in message news:<WyTXQKHJOegWCk+PNXR0cD3SWIYc@4ax.com>...
> On 21 Jun 2004 07:33:43 -0700, TeamHubbell@charter.net (Sean) wrote:
>
> >Hello,
> >
> > I do not seem to recall from Physics on how to do this. I have a
> >vector, say vector A. I also have a vector B. I would like to be able
> >to calculate a vector between these two, and then add a varing angle,
> >say theta, to the result so that I can perform some calculations. Here
> >is a simple pictorial:
> >
> >
> > C
> > /
> > /
> > /
> > / Theta
> >A --------------------- B
> >
> >So, basically, I would like to be given A, B and Theta, then calculate
> >the vectors my given offset theta value from 0-90 degrees.
> >
> >
> >Thanks in advance,
> >
> >Sean
>
> Your picture is a bit confusing. You call A and B vectors but show
> them as points. I assume you are talking about the vector from A to B
> which I will call V = < a, b >. (If A and B represent the heads of two
> undrawn vectors, then V = B - A). You want a vector W rotated
> counterclockwise from V by an angle theta. One way would be to use
> polar coordinates. Let alpha = arctan(b/a) if a > 0 and pi +
> arctan(b/a) if a < 0. Then let
>
> W = < cos(alpha + theta), sin(alpha + theta) >
>
> will give you a unit vector in the desired direction. Of course, if a
> = 0 alpha is +- pi/2 depending on the sign of b.
>
> --Lynn

Mr. Krutz, First thank you for your assistance. I understand
calculating the vector V. I was wondering if you might elaborate on
how to actually rotate V about A given a theta value.

Thanks again.

Sean

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