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Quickly compute the CMB powerspectra and matter transfer functions.
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PICO (Parameters for the Impatient Cosmologist)


To install PICO, download and extract the archive, and from the top folder run:

python build
python install

or, to automatically download the archive and install PICO in one command, run either of:

easy_install pypico


pip install pypico

depending on which is available on your system.

Install notes

  • If you don't have root access, you can append the option --user to any of these install commands to install PICO under your home directory instead of system wide.


Once you have PICO installed, to do anything you'll need some data files which actually contain interpolated data. You can find them on the PICO website at

After that, PICO is used from the Python shell. Typical usage starts by loading a PICO data file:

>> import pypico
>> pico = pypico.load_pico("example_pico_file.dat")

To show accepted input parameters call:

>> pico.inputs()

and to show outputted quantities call:

>> pico.outputs()

Finally, to run PICO call:

>> result = pico.get(outputs, **inputs)

where outputs is a list of outputs you actually want (or leave it unspecified to calculate all outputs), and **inputs is a dictionary of parameter values with keys for each input returned above. The return value result is a dictionary with a key corresponding to each output you requested.

Usage Notes

  • The PICO convention for multipole indexing is that an array entry arr[l] corresponds to the l-th multiple. Since Python is 0-indexed, this means the first entry in an array is the 0-th multiple.

  • The specification pico.get(outputs, **inputs) means get can be called in several ways, including:

    >> pico.get(param1=val1, params2=val2)
    >> pico.get(**{'param1':val1, 'param2':val2})
    >> pico.get(**dict(param1=val1, param2=val2))
    >> pico.get(param1=val1, **{'param2':val2})
  • Certain data files may contain a set of example input values which can be accessed with:

    >> pico.example_inputs()

Installing Plugins for CAMB and CosmoMC

Follow the instruction in this section if you'd like to,

  • Have your code which currently calls CAMB_GetResults used PICO instead
  • Have CosmoMC use PICO


When you installed PICO, a static library libpico.a was created which allows PICO to be called from C, C++, Fortran, or any other language which can understand the symbols in the library. To link your code against this library, PICO provides an easy way to get include and link flags on your platform. To print out the necessary flags, call:

python -c "import pypico; print pypico.get_include()"
python -c "import pypico; print pypico.get_link()"

You should put these calls directly in your Makefile via:

$(shell python -c "import pypico; print pypico.get_link()")

Plugin Folder

You can find the various plugin files in a folder plugin in the archive. If you installed PICO via pip or easy_install, you can find the location of the plugins by running:

python -c "import pypico; print pypico.get_folder()"

CAMB Plugin

If your code is set up to call the CAMB function CAMB_GetResults, then it should be trivial to use the PICO version called PICO_GetResults instead. The PICO version will fall back on the CAMB version if called with parameters for which it cannot calculate the relevant quantities.

To install the CAMB plugin, do the following:

  • Copy plugins/camb/pico_camb.f90 to the folder containing your code
  • In your Makefile, make sure pico_camb.f90 gets compiled.
  • Add a call fpico_load(file) to load a PICO datafile.
  • Replace CAMB_GetResults with PICO_GetResults
  • Add use pico_camb wherever you need PICO_GetResults
  • Compile your code, making sure to use the correct include/link flags (see Linking).
  • Add the key pico_datafile to your parameter file.

CosmoMC Plugin

PICO can also be plugged into CosmoMC.

To install the CosmoMC plugin, do the following:

  • Copy plugins/cosmomc/CMB_Cls_pico.f90 and plugins/camb/pico_camb.f90 to the CosmoMC source folder
  • Replace driver.f90 in the CosmoMC source folder with the one in plugins/cosmomc
  • In your CosmoMC Makefile, add the line CMB_Cls_pico.o: pico_camb.o
  • In your CosmoMC Makefile, replace references to CMB_Cls_simple with references to CMB_Cls_pico
  • Add the correct include/link flags to the Makefile (see Linking).
  • Add the key pico_datafile to your parameter file.

Known Issues

  • -fast with Intel Fortran does not work
  • The CosmoMC plugin does not support PICO datafiles which provide the WMAP likelihood.


The main author of PICO is Marius Millea (feel free to send questions/comments to

PICO was originally created by Chad Fendt and Ben Wandelt (see

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