Hi everyone, I think there is a small error in the angular momentum calculation. Below, L is calculated as: L = velocity x radius def _SpecificAngularMomentumX(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return yv*rv[2,:] - zv*rv[1,:] def _SpecificAngularMomentumY(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return -(xv*rv[2,:] - zv*rv[0,:]) def _SpecificAngularMomentumZ(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return xv*rv[1,:] - yv*rv[0,:] but it should be: L = radius x velocity This leads to a sign error (and gives me a whole load of retrograde GMCs!) def _SpecificAngularMomentumX(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return zv*rv[1,:] - yv*rv[2,:] def _SpecificAngularMomentumY(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return -(zv*rv[0,:] - xv*rv[2,:]) def _SpecificAngularMomentumZ(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return yv*rv[0,:] - xv*rv[1,:] Does that look right? Elizabeth ------------------------------------------------------ Elizabeth TASKER Assistant Professor Physics Department, Faculty of Science Hokkaido University Sapporo, Japan tasker@astro1.sci.hokudai.ac.jp http://astro3.sci.hokudai.ac.jp/~tasker/ ------------------------------------------------------
Hi Elizabeth, I think you're right, and Britton and I went over it to double check. I believe this should not have caused any issues as the L_vec is typically only used in analysis to get an axis (or to calculate the *Total* angular momentum) so this shouldn't be too big of an issue. But please do issue a pull request for this. Thanks for catching this! -Matt PS Initially I had to check how obtain_rvec worked to make sure it was also correct, and I believe it is. On Thu, Nov 8, 2012 at 4:00 AM, Elizabeth Tasker <tasker@astro1.sci.hokudai.ac.jp> wrote:
Hi everyone,
I think there is a small error in the angular momentum calculation.
Below, L is calculated as:
L = velocity x radius
def _SpecificAngularMomentumX(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return yv*rv[2,:] - zv*rv[1,:] def _SpecificAngularMomentumY(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return -(xv*rv[2,:] - zv*rv[0,:]) def _SpecificAngularMomentumZ(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return xv*rv[1,:] - yv*rv[0,:]
but it should be:
L = radius x velocity
This leads to a sign error (and gives me a whole load of retrograde GMCs!)
def _SpecificAngularMomentumX(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return zv*rv[1,:] - yv*rv[2,:] def _SpecificAngularMomentumY(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return -(zv*rv[0,:] - xv*rv[2,:]) def _SpecificAngularMomentumZ(field, data): xv, yv, zv = obtain_velocities(data) rv = obtain_rvec(data) return yv*rv[0,:] - xv*rv[1,:]
Does that look right?
Elizabeth
------------------------------------------------------ Elizabeth TASKER Assistant Professor
Physics Department, Faculty of Science Hokkaido University
Sapporo, Japan
tasker@astro1.sci.hokudai.ac.jp http://astro3.sci.hokudai.ac.jp/~tasker/ ------------------------------------------------------
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