= PDAF_correlation_function = 


This page documents the routine `PDAF_correlation_function` of PDAF. It was introduced with PDAF V2.3.

The routine provides the value of a chosen correlation function. It can be used, e.g. to generate non-diagonal observation error covariance matrices.

The interface is the following:
{{{
  SUBROUTINE PDAF_correlation_function(ctype, length, distance, value)
}}}
with the following arguments:
 * `ctype` : `integer, intent(in)`[[BR]] Type of weight function:[[BR]] (1) Gaussian function scaled to f(0)=1 [[BR]]  (2) 5th order polynomial with support radius sradius (Gaspari&Cohn 1999; 0 for distance>sradius)
 * `length` : `real, intent(in)`[[BR]] length scale:[[BR]] for (1) standard deviation[[BR]] for (2) cut-off length (f=0 for distance>=length)
 * `distance` : `real, intent(in)`[[BR]] Distance at which the function is evaluated
 * `weight` : `real, intent(out)`[[BR]] Function value