The meaure command supplies several algorithms for analyzing molecular
structures. In the following options, *selection* refers to an atom
selection, as returned by the `atomselect` command described in section
8.3.2. The optional *weight* must be either
`none`, an atom selection keyword such as `mass`, or a list of values,
one for each atom in the selection, to be used as weights. If *weight*
is missing or is `none`, then all weights are taken to be 1. When
an atom selection keyword is used, the weights are taken from *selection1*.

**center**: Returns the geometric center of atoms in*selection*[weight*weight*]*selection*using the given`weight`.**minmax**: Returns two vectors, the first containing the minimum , , and coordinates of all atoms in*selection**selection*, and the second containing the corresponding maxima.**rmsd**: Returns the root mean square distance between corresponding atoms in the two selections, weighted by the given*selection1**selection2*[weight*weight*]*weight*.*selection1*and*selection2*must contain the same number of atoms (the selections may be from different molecules that have different numbers of atoms).**fit**: Returns a 4x4 transformation matrix which, when applied to the atoms in*selection1**selection2*[weight*weight*]*selection1*, minimizes the weighted RMSD between*selection1*and*selection2*.**inverse**: Returns the inverse of the given 4x4 matrix.*matrix*

See section for more on RMSD alignment.