The Museum of HP Calculators

# Poisson probabilities for the HP-11C

This program is by Andrew Feist and is used here by permission.

This program is supplied without representation or warranty of any kind. Andrew Feist and The Museum of HP Calculators therefore assume no responsibility and shall have no liability, consequential or otherwise, of any kind arising from the use of this program material or any part thereof.

## Overview

Purpose:
Computes Poisson probabilities and cumulative probabilities.

Usage:
Type mu [enter] n [A] to calculate the probability of n successes in a Poisson experiment with parameter mu.
Type mu [enter] n [E] to calculate the probability of n or fewer successes in a Poisson experiment with parameter mu.

Memory:
The program A uses two registers (1-2 in the given listing), and the program E uses four (0-2 in the given listing, plus the I register). The other stack positions are maintained.

Notes:
Program E does not correctly handle n=0 (it will return the result for n=1); however, since no adding is necessary, program A can be used instead. Also, program E does not use program A, so either one can be used independently of the other.

## Listing

```001 f-LBL A
002 STO 1
003 x<->y
004 STO 2
005 x<->y
006 y^x
007 RCL 1
008 f-x!
009 /    (divide)
010 RCL 2
011 CHS
012 e^x
013 X
014 g-RTN
015 f-LBL E
016 x<->y
017 STO 2
018 g-CLx
019 1
020 0
021 0
022 0
023 /     (divide)
024 1
025 EEX
026 5
027 CHS
028 +
029 1
030 STO 1
031 +
032 STO I
033 g-CLx
034 1
035 f-LBL 4
036 RCL 2
037 X
038 RCL I
039 g-INT
040 /     (divide)
041 STO + 1
042 f-ISG
043 GTO 4
044 g-CLx
045 RCL 2
046 CHS
047 e^x
048 STO X 1
049 g-CLx
050 RCL 1
051 g-RTN```