5

In https://peerj.com/preprints/3190.pdf section 4.3

SHFs simulate the errors we would have made had we used this forecasting method at those points in the past.

The meaning I could understand is change "had" to "when", like

SHFs simulate the errors we would have made when we used this forecasting method at those points in the past.

I can't understand what is this "had" used for.

10

"had we used this forecasting method" means that the forecasters did not use that forecasting method in the past, but if they had, then a certain amount of error would have occurred. SHF is a technique to simulate what those hypothetical errors would have been.

In short we are dealing with an unreal past here, which is why the "had"-form is used.

I really think this paper may not be the best example to work on.

  • Thank you again!I am using github.com/facebook/prophet to do some researching , this is facebook officical paper, I have to read this to know the detail. – Mithril Mar 22 at 7:50
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    @Mithril I don't knw your background, but based on the questions you are asking, i suspect you would do well to improve your general English skills before tackling this kind of writing. If you do go ahead, you need to read very carefully and understand subjunctive forms, which are frequently used in such work. Also, note that the technical meaning of "horizon" was given in an earlier section than the one you quoted. This will be true of other words used in a technical manner. – David Siegel Mar 22 at 7:56
21

Your quotation is an example of a past unreal conditional sentence with inversion that is more formal than those that follow the usual word order:

SHFs simulate the errors we would have made had we used this forecasting method at those points in the past.

The usual word order would have been as follows:

SHFs simulate the errors we would have made if we had used this forecasting method at those points in the past.

This said, more about inversions in conditionals, can be read here.

  • 1
    I think that "used" should be bolded in either both sentences or neither, for easier comparison. – Acccumulation Mar 22 at 19:24
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    Indeed, you've spotted that. Done, @Acccumulation. – Lucian Sava Mar 22 at 19:37

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