Petrus Method

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Petrus method
Petrus method.gif
Information about the method
Proposer(s): Lars Petrus
Proposed: 1981
Alt Names: none
Variants: Petrus-W
No. Steps: 7
No. Algs: 2 to 493 (for the last layer)
Avg Moves: ~50
Purpose(s):
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Scrambled cube -> 2x2x2 Block -> 2x2x3 Block -> EO Petrus -> Petrus F2L -> LL+EO:CP -> LL+EO+CP:CO -> EPLL -> Solved cube


Petrus was the second most popular speedcubing method behind CFOP.

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The Petrus Method, invented by Lars Petrus, is a block-building method where the F2L is solved intuitively with no algorithms. Petrus used to be the second most popular speedcubing method behind Fridrich/CFOP; however nowadays it is often considered to be outdated as it has been steadily declining in popularity since the rise of the "Big Three" (CFOP, Roux and ZZ).

The Petrus Method is sometimes partially used in CFOP solves for XCross.

The Steps

The following steps describe an approach suited for beginners, more advanced users might combine steps 1 and 2 and/or 5 and 6 (COLL) or use a Fridrich type last layer and do OLL and then PLL. If the fifth step is skipped the last layer can be solved with a 2GLL algorithm.


1. Build a 2x2x2 block anywhere on the cube.

2. Expand the 2x2x2 block to a 2x2x3 block; three ways are possible for each initial 2x2x2 block placement.

3. Fix the "bad edges" (in other words, orient the remaining seven edges on the cube that have not been solved).

4. Finish the First Two Layers (F2L) by only turning 2 sides. The pure Petrus approach is to create a 1x2x2 block and expand it to a 1x2x3 block to finish off the F2L, not to solve the cross piece and two corner/edge pairs; two ways are possible. The last-layer edges will orientate themselves automatically.

5. Permute the last-layer corners (put them in their correct places).

6. Orient the last-layer corners, making the whole last layer a solid colour.

7. Permute the last layer edges, without disturbing the other pieces, to solve the cube.

Pros

  • The Petrus Method uses fewer moves than the Fridrich method and most, if not all, other non-block-building methods.
  • It is more intuitive than the Fridrich method, and it requires far fewer algorithms.
  • It requires fewer algorithms than some beginner methods (including the most popular one: Layer By Layer).
  • If COLL is used as well, one can orient and permute the corners at the same time.
  • The last layer can even be solved in one look with ZBLL or ZZLL, however this drastically increases the number of algorithms one must learn.

Cons

  • It can be sometimes hard (especially for a beginner) to optimize block building, and it's difficult to keep consistently turning throughout the solve.
  • Due to the high amount of intuition, it is difficult to optimize finger tricks during the block building stage.
  • Recognition in the Edge Orientation step tends to result in long pauses.

Petrus variations

  • Petrus-W: ZZ-style EO is used to finish to final two CE Pairs with only R U L moves while not placing the Down-Front edge. COLL and L5EP is then used to finish the cube.

Petrus as a Beginner Method

Used as a beginner method, Petrus requires much more intuition, but also involves learning fewer algorithms. For a tutorial, see the external links below.

Petrus on other puzzles

Methods based around the Petrus' idea of blockbuilding and then orienting the remaining edges have also been created for other puzzles. Here is a list of puzzles and Petrus-like methods for them:

External links