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pyRMSD is a small Python package that aims to offer an integrative and efficient way of performing RMSD calculations of large sets of structures. It is specially tuned to do fast collective RMSD calculations, as pairwise RMSD matrices.


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pyRMSD goal is the fast (and easy!) calculation of rmsd collective operations, specially matrices of large ensembles of protein conformations. It also offers a symmetric distance matrix implementation with improved access speed and memory efficiency.

If you like it and you are using it for your scientific projects, please cite the pyRMSD paper:

Bioinformatics (2013) 29 (18): 2363-2364.
doi: 10.1093/bioinformatics/btt402

pyRMSD distributed under MIT license, and it is currently on its version 4.0 .


##1 - Features ###Collective operations pyRMSD currently has 5 basic operations: 1 - Pairwise RMSD calculation 2 - One vs. following (of a sequence of conformers). 3 - One vs. all the other conformations (of a sequence of conformers). 4 - Pairwise RMSD matrix 5 - Iterative superposition of a sequence.

All methods can use the same coordinates for fitting and RMSD calculation, or a different set of coordinates for fitting (superposing) and calculating RMSD (referred into the code as 'calculation coordinates' ).

Currently pyRMSD implements a total of 3 superposition algorithms (Kabsch's,QTRFIT and QCP) which can have serial or parallel versions (OpenMP and CUDA in one case).

The available calculators so far are:

  • QCP_CUDA_CALCULATOR (in CUDA capable machines*)
  • QCP_CUDA_MEM_CALCULATOR (in CUDA capable machines*)

In addition it offers 2 other calculators that do not perform superposition (for cases in which the parts of interest of the system are already superposed):

  • NOSUP_OMP_CALCULATOR This calculator will also center the coordinates, adding a little unnecessary overhead. This overhead will be totally diluted when calculating RMSD matrices though.

Finally it also holds a hidden calculator, QCP_SERIAL_FLOAT_CALCULATOR, maninly used to test against QCP_CUDA_CALCULATOR in its float version.

Methods 1, 2 and 3 can be used to modify the input coordinates (the input coordinates will be superposed). The iterative superposition method will always have this behaviour as it would be senseless otherwise. Conversely, RMSD matrix will never modify input coordinates.

pyRMSD can also have fitting symmetries and rotational calculation symmetries into account. Documentation about this is on its way.

If you think you need new features to be added (or better examples) click here. * Computing capability of the GPU must be equal or higher than 1.1 (>1.2 if built with double precision support). ###Condensed matrix pyRMSD contains also a C written data type called CondensedMatrix. This is a representation of a squared symmetric matrix and it will save you half of the, otherwise redundant, memory. Besides, its write and read access outperforms other implementations like pure python's list-based and even Cython implementations (see the benchmarks folder). This means that it will speed up for free any application that heavily relies on accessing a distance matrix, like clustering algorithms. See the examples below to get more insight about how to use it. ##2 - Usage Some code snippets and explanations about them will be shown below. Note that, as the code changes rapidly, this snippets can be outdated. I will put all my effort for this not to happen, but if you detect that the code examples are being more problematic than helpful for you, please contact me. You will also find method and variables documentation in the code. Do not hesitate to ask for more documentation if you find is missing.

###Getting coordinates To use the module the first thing will be to extract all the coordinates from a PDB file. Coordinates must be stored in numpy arrays, using the same layout that Prody uses:

Coordset: [Conformation 1, Conformation 2, ..., Conformation N]
Conformation: [Atom 1, Atom 2,..., Atom M]
Atom: [x,y,z]

In order to do this there's a convenience class function in pyRMSD/utils/ called Reader. This will read a pdb file using the built in reader. Despite this, we encourage the use of Prody if you need to do any kind of selection/manipulation.

from pyRMSD.utils.proteinReading import Reader
reader = Reader().readThisFile("my_trajectory.pdb").gettingOnlyCAs()
coordinates =
num_of_atoms = reader.numberOfAtoms
num_of_frames = reader.numberOfFrames

See 'pyRMSD/pyRMSD/test/ for a simple usage example. ###Calculating the RMSD matrix To calculate the RMSD matrix you can use a MatrixHandler or use directly one calculator object to feed a CondensedMatrix.

Using MatrixHandler to get the RMSD pairwise matrix (given that we already have read the coordinates) will look like this:

from pyRMSD.matrixHandler import MatrixHandler

rmsd_matrix = MatrixHandler()\
   .createMatrix(coordinates, 'QCP_OMP_CALCULATOR')

Calculating the matrix using directly the RMSDCalculator is a little bit more verbose:

import pyRMSD.RMSDCalculator

calculator = pyRMSD.RMSDCalculator.\
rmsd = calculator.pairwiseRMSDMatrix()
rmsd_matrix = CondensedMatrix(rmsd)

As the resulting matrix is symmetric and its diagonal is 0, the rmsd_matrix object will store only the upper diagonal triangle (condensed matrix), in the same way scipy.spatial.distance.pdist does. ###Available calculators Programatically, available calculators can be queried with:

from pyRMSD.availableCalculators import availableCalculators

print availableCalculators()

###Matrix handlers A MatrixHandler object will help you to create the matrix and will also help you saving and loading matrix data to disk.

from pyRMSD.matrixHandler import MatrixHandler

# Create a matrix with the coordsets and using a calculator
mHandler = MatrixHandler()
matrix = mHandler.createMatrix( coordsets,\

# Save the matrix to 'to_this_file.bin'

# Load it from 'from_this_file.bin'

# Get the inner CondensedMatrix instance
rmsd_matrix = mHandler.getMatrix()

###Accessing the RMSD matrix You can access a matrix object contents like this:

rmsd_at_pos_2_3 = rmsd_matrix[2,3]

The row_lenght parameter will give you the... row length. Remember that the matrix is square and symmetric, so row_length == column_length, rmsd_matrix[i,j] == rmsd_matrix[j,i] and as it is a distance matrix, rmsd_matrix[i,i] == 0.

One can also access the inner representation of the data (a numpy array) using the get_data( ) function. Ex.

inner_data = rmsd_matrix.get_data()  

The inner_data array will contain only the elements of the matrix upper triangle (diagonal not included), in row-major order. for example, the matrix:

0 1 2 3 4
1 0 5 6 7
2 5 0 8 9
3 6 8 0 1
4 7 9 1 0

Will be retrieved as:

[1, 2, 3, 4, 5, 6, 7, 8, 9, 1]

It is possible to use scipy.spatial.distance.squareform in order to recover the initial matrix layout.

###Matrix statistics The CondensedMatrix class also offers an efficient way to ask for the most common statistical moments. Use the methods calculateMean, calculateVariance, calculateSkewness and calculateKurtosis to get mean, variance, skewness and kurtosis ( easy, isn't it :) ). You can also use calculateMax and calculateMin to get the maximum and minimum value of the matrix.

##3 - Building & Installation ###Before installation Users only need to install Python version 2.6/2.7 (pyRMSD has only been tested with those, however it may work with another versions of the Python 2.X family). Numpy is also required. Surely you already have it into your machine, but, in the case you don't, it can be found here. There you will be able to find installers for almost all the combinations of platforms and Python versions you can think about.

Developers may remember that header files of Python and Numpy may be accessible, and your Python installation must contain the python shared library. This usually means that you have to compile it using ./configure --enable-shared before building Python (usually 2.7 distributions already come with this library). Prody is not a dependency, but I encourage its use to handle coordinates, as it is well-tested and powerful tool.

###Linux and MacOs

Those users have the following choices:

1) Using the '' file inside the root folder by typing:

> python install

with superuser privileges. Use 'build' instead to only build it. This is the usual way python packages are deployed. As 'distutils' do not support CUDA directly, your package will not be able to use CUDA calculators.

2) Using the custom script in pyRMSD main folder. This will compile a version of pyRMSD following your configuration details. To finish the installation you will need to change your PYTHONPATH in order to point to the parent folder of the package (or copy it in a folder already inside your PYTHONPATH). See this if you have any problem modifying it.


Windows Installation is discontinued. I keep some very basic instructions here though.

##4 - The custom building script pyRMSD includes a small build script that is indeed a recipe to compile the C extensions of pyRMSD. The script is the most versatile way to compile pyRMSD and will work in almost all situations. With this script one can build x86 and x64 distributions with enabled or disbled CUDA calculators. Invoke it from pyRMSD root folder with:

> python \[OPTIONS\]

By default this script won't do anything. OPTIONS can be one of these:

--build -> to compile pyRMSD (OpenMP version). --cuda single/double -> to compile it with single or double precission (you must specify only one). Double precission will not work in old cards even if they are CUDA capable. --clean -> Will remove any generated .o files. --build --clean is a good combination if you are not a developer. --clean-all -> Will remove all generated files. Combine this one with any other is not a good idea. It will remove any useful built file. --build-conf -> Will determine the file (inside build_conf folder) storing the configuration info. --help/-h -> Will write some hints about the options.

This script uses distutil's sysconfig package to get the search path for python headers and libs automatically. The building script will try to guess the location of the needed files for compilation, but it can be easily modified to be able to handle all kind of scenarios.

Configuration files

As stated before, multiple configuration files can be used by the building script to feed it with the correct variables. This configuration files are stored in the build_conf folder and by default, the 'default.conf' file is loaded (equivalent to --build-conf default.conf). These are the parameters that can be changed. If one key is not present in the file, then the contents of the key inside the 'default.conf' file are used.

  • "CUDA_BASE": Base folder of the CUDA distribution installed.
  • "CUDA_INCLUDE_FOLDER": Folder inside CUDA_BASE where CUDA headers are found.
  • "CUDA_LIBRARIES_FOLDER": Folder inside CUDA_BASE where CUDA libraries are found.
  • "CUDA_ARCHITECHTURE": Arquitecture of the GPU (in the sm_XX format).
  • "CUDA_LIBRARY": Name of the cuda library (usually 'cudart').
  • "CUDA_OPTIONS": Some options for the CUDA compiler.
  • "DEFINE_USE_CUDA": Allows to redefine the macro that tells the preprocessor that CUDA is going to be used. Changing this means you also changed parts of the code, so is not adviced.
  • "PYTHON_EXTENSION_OPTIONS": Compiler options usually added to compile Python extensions.
  • "PYTHON_INCLUDE_FOLDER": If "AUTO" it will use 'distutils.sysconfig' to obtain the location of Python's header files, if not it must be the full location of python's header files folder.
  • "PYTHON_LIBRARY_FOLDER": If "AUTO" it will use 'distutils.sysconfig' to obtain the location of Python's libraries. If "AUTO_ALT", it will use os.path.dirname (useful for those situations in which 'distutils.sysconfig' fails to get the propper folder). The other option is the full location of python's libraries folder.
  • "PYTHON_LIBRARY" : The python library to link against.
  • "OPENMP_OPTION" : The openmp flag for the compiler used (nowadays the only compiler is gcc, so this flag must be -fopenmp in almost all cases).
  • "NUMPY_INCLUDE" : If "AUTO" it will use ''numpy.get_include' to get the folder where numpy headers are. If not it must be the full path of this folder.
  • "PYTHON_EXTENSION_LINKING_OPTIONS": Compiler options usually added to link Python extensions.

See the examples into the build_conf if you want to create your own configuration files.

###Unix-based systems The building script was used in a Ubuntu x86 and Ubuntu x64 Os, as well as in MacOs (Snow Leopard) to perform a non CUDA build. It had the python-dev package installed, so python headers were available. PYTHON_X constants were left unchanged. It was also used under Ubuntu x64 with CUDA 4.2 to build the CUDA enabled version. ####Mac Users Roman Sloutsky warns that if you're not able to compile using the build script with default configuration options, just try to change "PYTHON_LIBRARY_FOLDER":"AUTO" to "PYTHON_LIBRARY_FOLDER":"AUTO_ALT" in "default.conf". Creating a new configuration file with only this entry will also work.

###Windows systems A preliminary version of the build script was also tested in Windows 7 32 and 64 systems using MinGW compiler tools. Here are the steps followed to succesfully compile the extensions:

- Download and install MinGW. Then add its /bin folder to Windows PATH
- Download and install Python 2.7.3
- Download and install Numpy (tested with v. 1.7.0 for python 2.7)
- [Optional] Download and install Prody (tested with v. 1.4.1 for python 2.7)

PYTHON_INCLUDE_FOLDER and PYTHON_LIBRARY_FOLDER constants were changed to match our Python installation paths. PYTHON_EXTENSION_LINKING_OPTIONS and PYTHON_EXTENSION_OPTIONS were also changed to fit Windows extension creation options. Once everything is built, create (or modify) the PYTHONPATH system variable and make it point the pyRMSD folder.

Modifying system variables

In order to create or modify a system variable under Windows 7, you will have to go to Control Panel -> System and Security -> System -> Advanced System Settings.

##5 - Testing (Developers) Once installed you can run the tests in pyRMSD/test using:

> python -m unittest discover

Currently only the test_create_with_reader test will fail if all the dependencies are fullfilled (it's unwritten yet). If you didn't build pyRMSD with CUDA support, 5 tests will be skipped.

If you compiled the package using the build script, an extra test suite will be available in the src/calculators/test folder with pure C tests. Run it inside this folder with ./test_rmsdtools_main

##6 - Benchmarks (Developers) Also available to users, inside the /benchmark folder, there are the benchmarks used to assess the performance of pyRMSD. There one can find some small scripts to test OpenMP parametrizations, calculation time of every implementation or even a small floating point error check.

##TODO If you have used this package and you feel something is missing/incorrect or whatever, you can change it and contribute. Some examples of things that need to be improved are:


  • Separate condensed matrix as new project.
  • Add distributed matrix calculation for VERY BIG datasets.
  • Add more comments...
  • Adding number of threads option for any OpenMP calculator.
  • Adding number of blocks and threads per block option in CUDA calculator.
  • Create a unique installer using Python distutils (difficult because of the use of CUDA).
  • Convert in a Makefile generator.
  • and of course improve this README!!


  • Solving bug in the CondensedMatrix object (erroneous creation when using a numpy array).
  • C code must be revised and further simplified.
  • Improve performance even more (less ops, simd ops ... etc).
  • Names in C code must be more self-explanatory.
  • Ecapsulate function arguments ( major refactoring).
  • Add more comments...
  • Add more and better tests to increase coverage.
  • OpenCL version.

###Condensed Matrix

  • Matrix generation load balance can be improved.
  • Symmetry features need to be explained.
  • Improve symmetry handling.
  • Change rules of array acceptance (add FLOAT32 and FLOAT16)
  • Improve single element data retrieval.


  • High level wrapper for atom selection as gist or separate project.
  • Hungarian algorithm to autodetect symmetries (see this paper and this package).
  • Currently only used with the fitting+calculation scheme. It would be gret to add them to the fitting-only scheme.

If you want to add new features (for instance mass weighting) do not hesitate to contact me at: victor.gil.sepulveda at Of course, you can fork the repository and add as many features and improvements as you want.


  • Some Numpy helper functions were first seen in, by Lou Pecora (if I'm not wrong).

  • The initial Python implementation of superposition was extracted from Prody source code (by Ahmet Bakan) and modified, with the only goal of providing a python example to compare performance and stability. The iterative superposition algorithm is a direct translation of his iterpose algorithm.

  • QCP superposition method code was adapted from the code here.

  • The statistics function code was adapted from the work of (available here ).

  • Kabsch algorithm code was adapted from the work of Dr. Bosco K. Ho. I would like to give him special thanks for his help.

  • As far as I know the first CUDA implementation of QCP is from Yutong Zhao. He went a step further trying to improve memory coalescence by changing the coordinates overlay. Pitifully his code is not open source.


pyRMSD is a small Python package that aims to offer an integrative and efficient way of performing RMSD calculations of large sets of structures. It is specially tuned to do fast collective RMSD calculations, as pairwise RMSD matrices.