# Chain Break Fraction

Where is chain break fraction in the D-Wave literature?  How can chain break fraction be influenced in the Advantage system where there does not seem to be a 'chain strength' parameter?

1 comment
• Hi Richard,

Chain break fraction is a fraction of chains in a sample that are broken. For example, if a sample has 8 chains and one of them is broken then chain_break_fraction is 0.125. So, it is preferred to have a low chain_break_fraction.

Here is a good resource that goes over chains and chain breaks: https://support.dwavesys.com/hc/en-us/community/posts/360016697094-What-is-a-chain-

As the chains are formed during minor-embedding the logical problem onto physical qubits, Ocean composites, such as EmbeddingComposite, include chain_strength parameter. So, this parameter is not solver dependent.

I also want to mention that the new release of Ocean SDK now includes a default chain_strength. Rather than using a static default, we now calculate the chain strength using the uniform_torque_compensation function, which takes the RMS of the problem's quadratic biases. This function can also be used to tune the chain strength by adjusting the prefactor.

Note that you need to upgrade to the Ocean 3.0 version to take advantage of this functionality.

Please let us know if you have any further questions.