Misorientation calculations

[kshankar7]

I am trying to find mis-orientation between two orientations (q1, q2) defined by two quaternions. My material is defined using a h5 file and is read in (qsym). To calculate misorientation I am using the following function call. Can you help me if this is correct? Any help in this would be greatly appreciated.

from hexrd.material import Material
from hexrd import rotations  as rot

mat = Material(name='Al_7085', 
               material_file='materials.h5')

qsym = mat.planeData.getQSym()

angle, mis_ori = rot.misorientation(_q1, _q2, ([qsym]))

@darrencpagan

[donald-e-boyce]

I improved the documentation for rotations.misorientation and created a test file in pull request #644.

In your example:

angle, mis_ori = rot.misorientation(_q1, _q2, ([qsym]))

The variable _q1 should be a single quaternion (shape (4, 1)); _q2 an array of quaternions (4, n); the third argument should just be (qsym,), which is a 1-tuple. The results will be angle, a scalar array of length n, and mis_ori, a quaternion array of shape (4, n).

The new documentation looks like:

def misorientation(q1, q2, *args):
    """
    PARAMETERS
    ----------
    q1: array(4, 1)
        a single quaternion
    q2: array(4, n)
        array of quaternions
    *args: tuple
        there can be only one extra argument, which is 1- or 2-tuple with
        symmetries (quaternion arrays); for crystal symmetry only,
        use a 1-tuple; with both crystal and sample symmetry use a 2-tuyple

    RETURNS
    -------
    angle: array(n)
        the misorientation angle between `q1` and each quaternion in `q2`
    mis: array(4, n)
        the quaternion of the smallest misorientation angle
    """

[donald-e-boyce]

One more comment on some python details.

Starting with your final line.

angle, mis_ori = rot.misorientation(_q1, _q2, ([qsym]))

That would work if you added the * operator.

angle, mis_ori = rot.misorientation(_q1, _q2, *([qsym]))

The python *args mechanism takes a list of further arguments. You can just give them directly without the *, or if they are in a list, then the * expands the list. So you could also write:

angle, mis_ori = rot.misorientation(_q1, _q2, [qsym])

There you are using a list instead of a tuple, which is fine, but if you wanted to use a tuple, it would be:

angle, mis_ori = rot.misorientation(_q1, _q2, (qsym,))

You need the comma to make it a tuple. Otherwise, it will just be parentheses around a single item that have no effect, i.e. (qsym) is the same as qsym.