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270

RECURSE

This functions is provided for programmers to

let them define functions in the Sequence

aplet.

For example, typing RECURSE(U,U(N-1)*N,1,2) U1(N) seemingly

produces no useful result in the HOME view, but would produce the result

shown right in the SYMB view of the Sequence aplet. The resulting sequence

is the factorial numbers.

The syntax is:

RECURSE(<seq.name>,<defn of term n>,<1st term>,<2nd term>)

and it must be ed into a sequence such as U1,U2..U9,U0 for it to have

any meaning.

(SUMMATION)

This function, also available on the keyboard, offers a way of calculating the

results of summation notation problems. The syntax of the function is

ordered in the same way as one reads a summation expression (see the

examples below).

Eg. 1

∑

which expands to

22222

12345

+++ giving an answer of 55,

can be evaluated using

(I=1,5,I

)

Eg. 2

∑

where

12345 6

2, 10, 13, 11, 20, 2xxxxx x=− = = = =− =

can be evaluated by first defining a list L1 as {-2,10,13,11,-20,2}

and then calculating

(I=1,6,L1(I))

Note: Although ‘i’ was used as the summation

index in each of the cases above, there

is nothing special about them. ‘i’ and ‘j’

are simply the letters traditionally used

in mathematical problems.

HP 39G Master Guide

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