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Isn't this book essentially a library written by experts[1] in numerical processing?

You can't just use a library by experts. You have to know or learn how to evaluate said library for correctness, efficiency, and stability (numerical and operational). If you know how to do that, you may be able to use a flawed library as a tool to get the shape of your processing quickly and fill in the rest of the details yourself.

[1] They've published a major book through three editions and the book cover calls them leading scientists.