ccdfstd : computes the standard deviation of any variable
-----------------------------------------------------------

Computes the standard deviation of any variable. This computation is
direct and does not required a pre-processing with any of the cdfmoy
tools. This is the wrapping around the native cdfstd operator assuming
its usage is::  

 cdfstd [-save] **[-spval0]** **[-nomissincl]** **[-stdopt]**
 ... list_of_files  

CliMAF optional arguments are the ones surrounded with '**'.

See also:

  - :doc:`ccdfstdmoy <ccdfstdmoy>` for also getting the mean value of
    the field  

**References** : http://www.drakkar-ocean.eu/tools

**Provider / contact** : climaf at meteo dot fr for the wrapping

**Inputs** (in the order of CliMAF call): 

  - any dataset forming a time-series (but only one)

**Mandatory arguments**: None

**Optional arguments**:

  - ``opt`` may be used to pass following keys :

    - ``-spval0`` : set missing_value attribute to 0 for all output
      variables and take care of the input missing_value. This option
      is usefull if missing_values differ from files to files  

    - ``-nomissincl`` : with this option, the output std and mean are
      set to missing value at any gridpoint where the variable
      contains a missing value for at least one timestep. You should
      combine with -spval0 if missing values are not 0 in all the
      input files 
      
    - ``-stdopt`` : use a  more optimal algorithm to compute std and
      std is unbiased 

**Required files**: None

**Outputs**:

  - main output : a netcdf file (variable : IN-var_std, same units
    than input variables) 

**Climaf call example**:: For more examples which are systematically
tested, see :download:`cdftools.py <../../examples/cdftools.py>` 

  >>> dmld=ds(simulation="PRE6CPLCr2alb", variable="omlmax", period="199807-199810", realm="O") # some dataset, with whatever variable
  >>> my_cdfstd=ccdfstd(dmld)
  >>> cfile(my_cdfstd) # to compute the standard deviation of variable "omlmax"

  >>> my_cdfstd2=ccdfstd(dmld,opt='-full')
  >>> cfile(my_cdfstd2)

**Implementation**: The operator is implemented as a binary using
cdftools cdfstd operator.