# 'Minimal' diff-algorithm producing a different result than 'myers', 'patience' and 'histogram' ones

2 messages from 2015-05-12 to 2015-05-24. Participants: Dmitry Malikov, Jeff King.
Thread: https://gitlist.dev/t/39309

## Dmitry Malikov, 2015-05-12 13:07

Subject: 'Minimal' diff-algorithm producing a different result than 'myers', 'patience' and 'histogram' ones
Message-ID: <CAAg4OeLuR9NY1NaEsjqd4hbuLqZuUo7j+BsVvQT37APY_QEYUQ@mail.gmail.com>
URL: https://gitlist.dev/e/CAAg4OeLuR9NY1NaEsjqd4hbuLqZuUo7j%2BBsVvQT37APY_QEYUQ%40mail.gmail.com

```
Good day,

I'm trying to compare 4 different git-diff algorithms and the
'minimal' one is the most vague and non-obvious. The documentation
says "Spend extra time to make sure the smallest possible diff is
produced." - that's all.

By any chance, is there any example of diff when 'minimal' algorithm
produces a different result than a 'myers', 'patience' and 'histogram'
ones?

PS: in case of a question like 'why do you need that?' - it's for
testing purposes of some git wrapper library.

```

## Jeff King, 2015-05-24 07:33

Subject: Re: 'Minimal' diff-algorithm producing a different result than 'myers', 'patience' and 'histogram' ones
Message-ID: <20150524073338.GA7197@peff.net>
URL: https://gitlist.dev/e/20150524073338.GA7197%40peff.net
In-Reply-To: <CAAg4OeLuR9NY1NaEsjqd4hbuLqZuUo7j+BsVvQT37APY_QEYUQ@mail.gmail.com>

```
On Tue, May 12, 2015 at 03:07:46PM +0200, Dmitry Malikov wrote:

> I'm trying to compare 4 different git-diff algorithms and the
> 'minimal' one is the most vague and non-obvious. The documentation
> says "Spend extra time to make sure the smallest possible diff is
> produced." - that's all.
> 
> By any chance, is there any example of diff when 'minimal' algorithm
> produces a different result than a 'myers', 'patience' and 'histogram'
> ones?

I don't know of a simple example offhand, but you can easily generate
all of the patches for a repository with each type by doing:

  for i in myers minimal patience histogram; do
    git log --diff-algorithm=$i -p >$i
  done

In git.git, the output for each type is distinct. You might also find
this thread interesting:

  http://thread.gmane.org/gmane.comp.version-control.git/143426

It mentions 717b83117 from git.git, whose minimal diff is over 300 lines
shorter than the non-minimal one. It's not exactly a simple example, but
I suspect you won't find a short case; "minimal" only matters in the
complicated ones.

-Peff

```