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Macros | Functions
autocorr.h File Reference
#include "gromacs/commandline/pargs.h"
#include "gromacs/utility/real.h"
+ Include dependency graph for autocorr.h:

Description

Declares routine for computing autocorrelation functions.

Author
David van der Spoel david.nosp@m..van.nosp@m.dersp.nosp@m.oel@.nosp@m.icm.u.nosp@m.u.se

Macros

#define eacNormal   (1<<0)
 Normal correlation f(t)*f(t+dt)
 
#define eacCos   (1<<1)
 Cosine correlation cos(f(t)-f(t+dt))
 
#define eacVector   (1<<2)
 Vector correlation f(t).f(t+dt)
 
#define eacRcross   (1<<3 | eacVector)
 Norm of cross product |f(t) (x) f(t+dt)|.
 
#define eacP0   (1<<4 | eacVector)
 Vector with Legendre polynomial of order 0 (same as vector)
 
#define eacP1   (1<<5 | eacVector)
 Vector with Legendre polynomial of order P_1(f(t).f(t+dt))
 
#define eacP2   (1<<6 | eacVector)
 Vector with Legendre polynomial of order P_2(f(t).f(t+dt))
 
#define eacP3   (1<<7 | eacVector)
 Vector with Legendre polynomial of order P_3(f(t).f(t+dt))
 
#define eacP4   (1<<8 | eacVector)
 Vector with Legendre polynomial of order P_4(f(t).f(t+dt))
 
#define eacIden   (1<<9)
 Binary identy correlation (f(t) == f(t+dt))
 

Functions

t_pargsadd_acf_pargs (int *npargs, t_pargs *pa)
 Add commandline arguments related to autocorrelations to the existing array. *npargs must be initialised to the number of elements in pa, it will be incremented appropriately. More...
 
int get_acfnout (void)
 Returns the number of points to output from a correlation function. Works only AFTER do_auto_corr has been called! More...
 
int get_acffitfn (void)
 Returns the fitting function selected. Works only AFTER do_auto_corr has been called! More...
 
void do_autocorr (const char *fn, const gmx_output_env_t *oenv, const char *title, int nframes, int nitem, real **c1, real dt, unsigned long mode, gmx_bool bAver)
 Calls low_do_autocorr (see below). add_acf_pargs has to be called before this can be used. More...
 
void low_do_autocorr (const char *fn, const gmx_output_env_t *oenv, const char *title, int nframes, int nitem, int nout, real **c1, real dt, unsigned long mode, int nrestart, gmx_bool bAver, gmx_bool bNormalize, gmx_bool bVerbose, real tbeginfit, real tendfit, int nfitparm)
 Low level computation of autocorrelation functions. More...
 

Function Documentation

t_pargs* add_acf_pargs ( int *  npargs,
t_pargs pa 
)

Add commandline arguments related to autocorrelations to the existing array. *npargs must be initialised to the number of elements in pa, it will be incremented appropriately.

Parameters
npargsThe number of arguments before and after (is changed in this function)
[in]paThe initial argument list
Returns
the new array
void do_autocorr ( const char *  fn,
const gmx_output_env_t *  oenv,
const char *  title,
int  nframes,
int  nitem,
real **  c1,
real  dt,
unsigned long  mode,
gmx_bool  bAver 
)

Calls low_do_autocorr (see below). add_acf_pargs has to be called before this can be used.

Parameters
[in]fnFile name for xvg output (may this be NULL)?
[in]oenvThe output environment information
[in]titleis the title in the output file
[in]nframesis the number of frames in the time series
[in]nitemis the number of items
[in,out]c1is an array of dimension [ 0 .. nitem-1 ] [ 0 .. nframes-1 ] on output, this array is filled with the correlation function to reduce storage
[in]dtis the time between frames
[in]modeDifferent types of ACF can be done, see above
[in]bAverIf set, all ndih C(t) functions are averaged into a single C(t)
int get_acffitfn ( void  )

Returns the fitting function selected. Works only AFTER do_auto_corr has been called!

Returns
the fit function type.
int get_acfnout ( void  )

Returns the number of points to output from a correlation function. Works only AFTER do_auto_corr has been called!

Returns
the output length for the correlation function
void low_do_autocorr ( const char *  fn,
const gmx_output_env_t *  oenv,
const char *  title,
int  nframes,
int  nitem,
int  nout,
real **  c1,
real  dt,
unsigned long  mode,
int  nrestart,
gmx_bool  bAver,
gmx_bool  bNormalize,
gmx_bool  bVerbose,
real  tbeginfit,
real  tendfit,
int  nfitparm 
)

Low level computation of autocorrelation functions.

do_autocorr calculates autocorrelation functions for many things. It takes a 2 d array containing nitem arrays of length nframes for each item the ACF is calculated.

A number of "modes" exist for computation of the ACF controlled by variable mode, with the following meaning.

Mode Function
eacNormal C(t) = < X (tau) * X (tau+t) >
eacCos C(t) = < cos (X(tau) - X(tau+t)) >
eacIden C(t) = < (X(tau) == X(tau+t)) > (not fully supported yet)
eacVector C(t) = < X(tau) * X(tau+t)
eacP1 C(t) = < cos (X(tau) * X(tau+t) >
eacP2 C(t) = 1/2 * < 3 cos (X(tau) * X(tau+t) - 1 >
eacRcross C(t) = < ( X(tau) * X(tau+t) )^2 >

For modes eacVector, eacP1, eacP2 and eacRcross the input should be 3 x nframes long, where each triplet is taken as a 3D vector

For mode eacCos inputdata must be in radians, not degrees!

Other parameters are:

Parameters
[in]fnis output filename (.xvg) where the correlation function(s) are printed
[in]oenvcontrols output file properties
[in]titleis the title in the output file
[in]nframesis the number of frames in the time series
[in]nitemis the number of items
[in]nout
[in,out]c1is an array of dimension [ 0 .. nitem-1 ] [ 0 .. nframes-1 ] on output, this array is filled with the correlation function to reduce storage
[in]dtis the time between frames
[in]modeDifferent types of ACF can be done, see above
[in]nrestartis the number of steps between restarts for direct ACFs (i.e. without FFT) When set to 1 all points are used as time origin for averaging
[in]bAverIf set, all ndih C(t) functions are averaged into a single C(t)
[in]bNormalizeIf set, all ACFs will be normalized to start at 0
[in]bVerboseIf set output to console will be generated
[in]tbeginfitTime to start fitting to the ACF
[in]tendfitTime to end fitting to the ACF
[in]nfitparmNumber of fitting parameters in a multi-exponential fit