## #1846 closed defect (invalid)

# maxima looses minus signs in symbolic expression

Reported by: | jkantor | Owned by: | William Stein |
---|---|---|---|

Priority: | major | Milestone: | sage-duplicate/invalid/wontfix |

Component: | calculus | Keywords: | |

Cc: | Merged in: | ||

Authors: | Reviewers: | ||

Report Upstream: | N/A | Work issues: | |

Branch: | Commit: | ||

Dependencies: | Stopgaps: |

### Description

Consider

log(a*e^(-a*x-b)).simplify_exp()

This gets expanded correctly, however

log(a*e^(-a*x-b)/(1+exp(-a*x-b))^2 ).simplify_exp()

appears to lose the minus signs on ax and b.

### Change History (3)

### comment:1 Changed 15 years ago by

Resolution: | → invalid |
---|---|

Status: | new → closed |

### comment:2 Changed 15 years ago by

Milestone: | → sage-2.10.1 |
---|

### comment:3 Changed 15 years ago by

Milestone: | sage-2.10.1 → sage-duplicate/invalid |
---|

**Note:**See TracTickets for help on using tickets.

Actually Sage is right and you are wrong, because of the identity

`log(e^(-a*x - b) + 1) == log(e^(a*x + b) + 1) - a*x - b`

which one can derive from Taylor expansions of`log(x+1)`

and`log(x^(-1) + 1)`

. See below.