# What does surrogate mean in this context?

I'm trying to learn about Gaussian Processes and ran into an interesting example on the scikit-learn documentation but am having trouble interpreting the line below.

Say we want to surrogate the function g(x) = x \sin(x).

What does surrogate mean in this context?

http://scikit-learn.org/stable/modules/gaussian_process.html

Caveat I was curious because I didn't know myself, but here's my recently-informed best guess:

It looks like it really just means "fit." The wording certainly doesn't make it clear, but it seems like a better sentence using the same word would be "find a surrogate for the function ...", meaning, can we come up with a model that gets pretty close to $x\sin(x)$, or in other words, can we fit a curve to it.

Here is some of the reading I did to come to that conclusion. It talks about a "surrogate" as an approximate but tractable function that's used to replace a complicated function (in the case of optimization) but between that and the context of the example that scikit-learn gives, that looks like a good guess.

• To be fair to OP, the usage is confusing because surrogate is a noun, where the quotation uses it as a verb!
– Sycorax
Feb 2, 2016 at 1:03
• Totally fair -- yeah, the sentence is quite strange. Feb 2, 2016 at 3:49
• @Sycorax: In English it seems like it is quite easy to use names/nouns as verbs, like to google May 3, 2021 at 20:06
• @kjetilbhalvorsen That's either an elision, as in "to [search] Google," or the informal phenomenon of promoting brand names to verbs (happened to Google and Xerox). I've consulted a dictionary, and it doesn't have a verb entry for "surrogate," only noun and adjective. My guess is that the author of the passage did what I often do, which is revise a document and erase a word by accident.
– Sycorax
May 3, 2021 at 20:14