bugAxiom Computer Algebra System - Bugs: bug #9216, differentiating sums with respect...


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bug #9216: differentiating sums with respect to a bound is wrong

Submitted by:  Martin Rubey <kratt6>
Submitted on:  Fri Jun 4 08:06:32 2004  
Category: NoneSeverity: 3 - Normal
Item Group: code bugStatus: transferred
Privacy: PublicAssigned to: None
Originator Name: kratt6Open/Closed: Open
Release: tla from may 2004Reproducibility: None
Fixed Release: 
Error message: 
Example of code trigerring the bug: 

f:=operator 'f

Internal cause: 

dvdsum in COMBF is mathematically incorrect

Mon Jun 21 11:12:28 2004, comment #1:

patch #3148

Martin Rubey <kratt6>
Fri Jun 4 08:06:32 2004, original submission:

(1) f:=operator 'f
(1) f
Type: BasicOperator
(2) -> D(sum(f(i),i=a..x),x)
(2) f(x) Type: Expression Integer

is nonsense. The problem is in COMBF/dvdsum:

dvdsum(l, x) ==
x = retract(y := third l)@SE => 0
k := retract(d := second l)@K
differentiate(h := third rest rest l,x) * eval(f := first l, k, h)
- differentiate(g := third rest l, x) * eval(f, k, g)
+ opdsum [differentiate(f, x), d, y, g, h]

Although this -- d/dx sum_i^x f(i) = f(x) -- is a nice try, it is wrong. It seems that the order of magnitude is roughly correct, but that's about it.

Unfortunately, I do not know how to return the thing unevaluated, so I cannot fix the bug yet

Martin Rubey <kratt6>


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Follow 2 latest changes.

Date Changed By Updated Field Previous Value => Replaced By
Wed Jun 22 18:55:30 2005billpage1StatusNone=>transferred
  Example of code trigerring the bugf:=operator 'f D(sum(f(i),i=a..x),x) =>f:=operator 'f D(sum(f(i),i=a..x),x)

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