HP 50g - summation

[Claudio L.]

(06-03-2016 12:47 PM)Simone Cerica Wrote:  Hello everyone, is there a way to make a summation in such a way that

'\GS(N=1,5,XN)' = 'X1+X2+X3+X4+X5' ?


Simone

How about this way?

Code:


<< -> N V 
<< 1 N FOR K
 'V' RCL
 ->STR TAIL HEAD K + STR->
NEXT
WHILE N 1 > REPEAT
+ 'N' DECR DROP
END
>>
>>

Store it in let's say XSUM, then:
'XSUM(5,X)' EVAL will produce what you want. It's limited to single-letter identifiers (by using TAIL HEAD, this can be improved).
Another improvement could be a start value for N, but you get the idea.

Quick footnote: For those trying this in newRPL, the TAIL HEAD combination needs to be removed, as the identifiers in symbolics are unquoted, then the code is good for arbitrary length identifiers.