You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: pr_spm_get_bf.m
    path of file: ./repos/bspm/thirdparty/spm12/toolbox/marsbar-0.44/@mardo_2/private
    
    the code of the file until where you have to start completion: function [xBF] = pr_spm_get_bf(xBF)
% fills in basis function structure
% FORMAT [xBF] = spm_get_bf(xBF);
%
% xBF.dt      - time bin length {seconds}
% xBF.name    - description of basis functions specified
% xBF.length  - window
    
function
	%---------------------------------------------------------------
	[bf p]         = pr_spm_hrf(dt);

	% add time derivative
	%---------------------------------------------------------------
	if findstr(xBF.name,'time')

		dp     = 1;
		p(6)   = p(6) + dp;
		D      = (bf(:,1) - pr_spm_hrf(dt,p))/dp;
		bf     = [bf D(:)];
		p(6)   = p(6) - dp;

		% add dispersion derivative
		%--------------------------------------------------------
		if findstr(xBF.name,'dispersion')

			dp    = 0.01;
			p(3)  = p(3) + dp;
			D     = (bf(:,1) - pr_spm_hrf(dt,p))/dp;
			bf    = [bf D(:)];
		end