Question about parallel operations on lists

*To*: mathgroup at yoda.physics.unc.edu*Subject*: Question about parallel operations on lists*From*: buchanan at guest2.math.ncsu.edu (Bob Buchanan)*Date*: Tue, 19 Jan 93 10:27:03 EST

Calling all Mma gurus, I'm coding some simple numerical methods for PDE conservation laws in one of my classes. Does anyone know a way to clean up the code of GodunovFlux[] (shown below) so that it doesn't require the Do[] loops? Flux[x_] := x (* simple flux function *) GodunovFlux[u_List,v_List] := Module[{diff,s,y,fluxu,fluxv}, diff = Abs[u-v] /. x_ :> 0 /; x < 1/1000; (* zero out any differences in u-v which are < 0.001 *) s = Table[0, {Length[u]}]; fluxu = Flux[u]; fluxv = Flux[v]; y = fluxv; (* if u-v != 0 then compute approximation to derivative *) Do[s[[i]] = If[diff[[i]] > 0, (fluxu[[i]] - fluxv[[i]])/(u[[i]] - v[[i]]), s[[i]]], {i,Length[u]}]; (* if previous result > 0 then y <- fluxu *) Do[y[[i]] = If[s[[i]] > 0,fluxu[[i]],y[[i]]], {i,Length[u]}]; y] Basically, I'm looking for an elegant (or arcane) way to avoid doing so much of this calculation element-wise. Thanks, Bob Buchanan (Bob_Buchanan at ncsu.edu)