*Requires RAM card for operation

The fx-820P is a printing member of Casio's BASIC pocket computer line. Even with a small thermal printer built-in, the device remains fairly small, compact, and usable. The built-in BASIC interpreter is the same interpreter found in literally dozens of different Casio models sold since the mid 1980s.

In other words, this machine is, well, slightly boring. No wonder I was admonished by Hugh Steers when he saw that the Gamma function examples I supply on these pages do nothing to alleviate the boredom! So, he sent me his own: an implementation in Casio BASIC that uses the Lanczos-approximation, but elegantly, computes the Lanczos coefficients on the fly, and does so within a reasonable amount of time, and with good precision. Apart from serving as evidence of Hugh's programming skills, the program also demonstrates just how useful and practical these handheld devices can be, even with their limited processing power and memory:

10 VAC:INPUT Z
20 H=1:A=-1:B=2
30 N=EXP 5.5/SQR 5.5
40 W=N/2:Y=.5:X=1:U=1
50 X=X*(Z+(1-U))/(Z+U)
60 N(U)=Y*EXP(U+5.5-LN(U+5.5)*(U+.5)):Y=Y*(U+.5)
70 FOR V=0 TO U:W=W+X*A(V)*N(V):NEXT V
80 IF U=6 THEN 130
90 T=A:FOR V=0 TO U
100 H(V)=2*T-H(V):T=B(V)
110 B(V)=2*H(V)-B(V):NEXT V
120 A=-A:U=U+1:GOTO 50
130 T=Z+.5:T=2*W*EXP(T*LN(T+5)-T-5)/Z
140 PRINT T