First, if you read through that scipy issue (https://github.com/scipy/scipy/issues/18118 https://github.com/scipy/scipy/issues/18118 ) the author was willing an

First, if you read through that scipy issue (https://github.com/scipy/scipy/issues/18118 https://github.com/scipy/scipy/issues/18118 ) the author was willing and able to relicense PRIMA under a 3-clause BSD license which is perfectly acceptable for scipy. For the numerical recipes reference, there is a mention that scipy uses a slightly improved version of Powell's algorithm that is originally due to Forman Acton and presumably published in his popular book on numerical analysis, and that also happens to be described & included in numerical recipes. That is, unless the code scipy uses is copied from numerical recipes, which I presume it isn't, NR having the same algorithm doesn't mean that every other independent implementation of that algorithm falls under NR copyright.