# Ticket #7212(closed defect: fixed)

Opened 4 years ago

## [with patch, positive review] steenrod algebra multiplication bug

Reported by: Owned by: jhpalmieri tbd minor sage-4.2 algebra William Stein John Palmieri sage-4.2.alpha0

### Description

From sage-support:

```I have Sage 4.1.1 install on a server, and I run the following code,
which outputs the following error:
sage: A3=SteenrodAlgebra(3)
sage: A3.P(36,6)*A3.P(27,9,81)
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call
last)
/home/user_bob/<ipython console> in <module>()
/usr/local/sage-4.1.1/local/lib/python2.6/site-packages/sage/structure/
element.so in sage.structure.element.RingElement.__mul__ (sage/
structure/element.c:9956)()
/usr/local/sage-4.1.1/local/lib/python2.6/site-packages/sage/structure/
element.so in sage.structure.element.RingElement._mul_ (sage/structure/
element.c:10021)()
/usr/local/sage-4.1.1/local/lib/python2.6/site-packages/sage/algebras/
steenrod_algebra_element.pyc in _mul_(self, other)
925                         new_dict = milnor_multiplication
(mono1, mono2)
926                     else:
--> 927                         new_dict = milnor_multiplication_odd
(mono1, mono2, p=p)
928                     for new_mono in new_dict:
929                         if result.has_key(new_mono):
/usr/local/sage-4.1.1/local/lib/python2.6/site-packages/sage/algebras/
steenrod_milnor_multiplication_odd.pyc in milnor_multiplication_odd
(m1, m2, p)
225                     t = tuple(diagonal[:i+1])
226                     if result.has_key((e,t)):
--> 227                         result[(e,t)] = F(coeff + result[t])
228                     else:
229                         result[(e,t)] = F(coeff)
KeyError: (26, 8, 86)
```

This is because of a simple bug: instead of result[t], it should be result[(e,t)].

## Change History

### comment:1 Changed 4 years ago by jason

• Status changed from new to needs_review

### comment:2 Changed 4 years ago by was

• Status changed from needs_review to positive_review
• Summary changed from [with patch, needs review] steenrod algebra multiplication bug to [with patch, positive review] steenrod algebra multiplication bug

### comment:3 Changed 4 years ago by mhansen

• Status changed from positive_review to closed
• Reviewers set to William Stein
• Resolution set to fixed
• Merged in set to sage-4.2.alpha0
• Authors changed from jhpalmieri to John Palmieri
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