Hi, I have a question about the option -tdiff in 3dTstat. According the instruction message,

-tdiff: Means to take the first difference of each time
series before further processing.

It is not clear what kind of further processing? I checked the relevant source code, it looks like this:

/* RWC: first difference here [25 May 2011] */

if( do_tdiff ){
float tsm , tss ;
ts_dif = (float*)calloc(npts, sizeof(float)) ;
for( ii=1 ; ii < npts ; ii++ )
ts_dif[ii-1] = ts[ii] - ts[ii-1] ;
get_linear_trend( npts-1 , ts_dif , &tsm , &tss ) ;
ts_mean = (double)tsm ;
ts_slope = (double)tss ;
npts-- ;
ts = ts_dif ;
}

It looks like the outputs are ts_mean and ts_slope. But I only get one output (the mean?). If I have time series of sin(t), would I get mean=0 and slope=0? Such results would not provide any information of the changes of the time series. Could any one please tell me a mathematical expression of the -tdiff output?

Thank you.