`cond` and `condskeel`

I am wondering about the usage of cond versus condskeel. I am familiar with the condition number, but not as much with the Skeel condition number. I have found that the two functions generally produce numbers of the same order of magnitude given a matrix, although condskeel is significantly faster. However, I am not sure if condskeel is intended to provide a cheaper estimate of the condition number. Moreover, condskeel optionally takes a vector, though I am not sure how the interpretation of condskeel changes when this vector is provided.

If anyone could point me to a resource on the Skeel condition number as defined in Julia, I would be grateful. Googling seems to have turned up little useful information for me.

numerical linear algebra - Skeel's condition number vs. classical condition number - Mathematics Stack Exchange has pretty good info here.

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