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 Aug 30 comment Simple exercise using the function Cases Addendum: for a sufficiently long list, exploiting the short-circuit property of Or[] can be helpful: test for divisibility by $3$ first, since it's the easier test, and invoke the primality test only if that fails. So, x_ /; Divisible[x, 3] || PrimeQ[x] Aug 30 comment How to delete subsets quickly? I see. @yohbs, what if you use Union[] with an appropriate SameTest setting? Aug 30 comment Combination of interpolations doesn't work? Good warning. In short: if your data is sufficiently contaminated with errors, direct application of finite differences will likely yield crap. You could try smoothing, but that is now a different kettle of fish… Aug 30 comment Simple exercise using the function Cases I had Select[list, Divisible[#, 3] || PrimeQ[#] &] in mind, tho. Aug 30 revised How to delete subsets quickly? edited tags Aug 30 comment How to delete subsets quickly? Without sorting, how long does it take? Aug 30 comment Simple exercise using the function Cases Select[] might be more straightforward for you. Aug 30 comment Undocumented function SumOfSquaresReps "number of arguments etc." - as you can surmise from kglr's answer, it takes two arguments: ReduceSumOfSquaresReps[k, n] returns all possible lists of k positive integers whose squares sum to n. Aug 30 comment Visualising a 1-(50,15,15) design @Shutao, it's block design notation. Aug 30 reviewed Leave Open Remove color artifacts in overlay of several Graphics objects? Aug 30 comment Calculating expected value from paired values and weights Equivalent: Dot @@ MapAt[Normalize[#, Total]&, Transpose[m], 2] Aug 30 revised Calculating expected value from paired values and weights user's additional comments Aug 30 reviewed Leave Open Removing an ordered pair from a list of ordered pairs according to a certain criterion Aug 30 reviewed Leave Open How to assert that a list of variables is real in a nice and clean way Aug 30 comment Decouple 3 simultaneous 2nd order ODEs (of 3 dependent variables) Why impose initial values for the second derivatives if your ODE is second-order? Aug 30 comment Calculating expected value from paired values and weights Times @@@ list? Aug 30 comment How to create pairwise difference matrix entry? Did you do what I said and look at the docs? Aug 30 comment How to create pairwise difference matrix entry? Look up Outer[]`. Aug 30 awarded Notable Question Aug 30 revised Visualising a 1-(50,15,15) design edited tags