Not enough input arguments

function [spei_index]=calculate_spei(t,prec,pevap,varargin);

[nlon, nlat, n]=size(prec);

prec=squeeze(prec);

for i=1:nlon

for j=1:nlat

if isnan(prec(i,j,1))==0

spei_index(i,j,:)=spei(t,prec(i,j,:),pevap(i,j,:),varargin);

else

spei_index(i,j,:)=ones(1,n-12)*NaN;

end

end

end

Error in calculate_spei (line 3)

[nlon, nlat, n]=size(prec);