title: how do you multiply a matrix to another with openMaya?
body: <p>I'm trying to create a script for mirroring transforms across the yz plane in Maya.</p>
  
  <p>I was able to set up a node network that gets the desired results.  I took a node at the origin with sz set to -1 and a source node from the left side (lf_grp for this test), and fed their worldMatrix attrs into a multMatrix node.  Then I passed the output (multMatrix.matrixSum) through a decompose matrix and into my destination node.</p>
  
  <p>I'd really prefer to not create a bunch of nodes to do my mirroring - running a create/connect/disconnect/delete cycle every time is slow and painful... I'd rather just "math the crap out of it" through my script, but I can't seem to figure out how to actually multiply my two matrices...</p>
  
  <p>Oh, I'm using the MTransformationMatrix since it handles a few things for you that the MMatrix does not - like rotation order (at least from what I've read...)</p>
  
  <p>Thank you for any help you can give!</p>
  
  <pre><code>import maya.cmds as mc
  import maya.OpenMaya as om
  
  src_xfm = 'lf_grp'
  mir_matrix_vals = [-1.0, -0.0, -0.0, 0.0,
                     0.0, 1.0, 0.0, 0.0,
                     0.0, 0.0, 1.0, 0.0,
                     0.0, 0.0, 0.0, 1.0]
  
  # get src xfm matrix
  #
  selList = om.MSelectionList()
  selList.add(src_xfm)
  mDagPath = om.MDagPath()
  selList.getDagPath(0, mDagPath)
  
  src_xfmFn = om.MFnTransform(mDagPath)
  src_matrix = src_xfmFn.transformation()
  
  # construct mir xfm matrix
  #
  mir_matrix = om.MTransformationMatrix()
  tmp_matrix = om.MMatrix()
  om.MScriptUtil().createMatrixFromList(mir_matrix_vals, tmp_matrix)
  mir_matrix = om.MTransformationMatrix(tmp_matrix)
  
  # multiply matrices to get mirrored matrix
  #
  dst_matrix = src_matrix * mir_matrix  # HOW DO YOU DO THIS????
  </code></pre>