--- a/scripts/specfun/betaln.m
+++ b/scripts/specfun/betaln.m
@@ -21,16 +21,17 @@
 ## Return the natural logarithm of the Beta function,
 ## @tex
 ## $$
-##  B (a, b) = \log {\Gamma (a) \Gamma (b) \over \Gamma (a + b)}.
+##  {\rm betaln} (a, b) = \ln (B (a,b)) \equiv \ln ({\Gamma (a) \Gamma (b) \over \Gamma (a + b)}).
 ## $$
 ## @end tex
 ## @ifnottex
 ##
 ## @example
-## betaln (a, b) = gammaln (a) + gammaln (b) - gammaln (a + b)
+## betaln (a, b) = log (beta (a, b))
 ## @end example
 ##
 ## @end ifnottex
+## calculated in a way to reduce the occurrence of underflow.
 ## @seealso{beta, betainc, gammaln}
 ## @end deftypefn
 
@@ -39,14 +40,18 @@
 ## Keywords: log beta special function
 
 function retval = betaln (a, b)
+
   if (nargin != 2)
     print_usage ();
   endif
 
   retval = gammaln (a) + gammaln (b) - gammaln (a + b);
+
 endfunction
 
-%!assert (betaln(3,4),log(beta(3,4)),eps)
+
+%!assert (betaln (3,4), log (beta(3,4)),eps);
 
-%!error (betaln(1.))
-%!error (betaln(1.,1.,1.))
+%% Test input validation
+%!error (betaln (1))
+%!error (betaln (1,2,3))