function y=expdata(A,B,N,M)
% expdata - exponential data sequence
%
% expdata :: 
%    real  ~'initial value',
%    real  ~'final value',
%    natural ~'number of steps (sequence length is steps+1),
%    M:natural ~'buffer size'
% -> seq [[1,M]].
lA=log(A);
k=(log(B)-lA)/N;
y=map(@(i)exp(lA+k*i),integers(0,N));
