Re: V8 slow like a snail

*To*: mathgroup at smc.vnet.net*Subject*: [mg127706] Re: V8 slow like a snail*From*: "Dr. Wolfgang Hintze" <weh at snafu.de>*Date*: Thu, 16 Aug 2012 01:55:36 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net*References*: <k0fjaj$q71$1@smc.vnet.net> <k0fqto$r07$1@smc.vnet.net>

On 15 Aug., 11:42, Roland Franzius <roland.franz... at uos.de> wrote: > Am 15.08.2012 09:32, schrieb Dr. Wolfgang Hintze: > > > > > > > Great disappointment on my side with 8.0.4.0 Home edition which I > > installed yesterday! > > My first impression: looks good, many nice features ... but incredibly > > slow in comparision to my good old 5.2. > > I then carried out a modest benchmark test the results of which I'll > > show below and which I like to express in terms of a "snail > > factor" ( = time in v5.2/ time in v8). > > > Consider this integral for which we can safely expect Mathematica to > > be expert in solving: > > > f1[n_, m_] := > > Integrate[n t^m Exp[-n t] (Exp[t] - 1)^(n - 1), {t, 0, \[Infinity]}= , > > Assumptions -> {{n, m} \[Element] Integers, m >= 0, n > 0}] > > > I carried out Timing[f1[n, m]] for m=0,1,2,3,10 in both versions. Her= e > > are the results in the format > > > {m, V5.2 f1 first call, V5.2 second call, V8 first call, V8 second > > call, snail factor first call, snail factor second call} > > > { > > { 0, 0.328, 0.078, 2.122, 2.044, 6.46951, 26.2051}, > > { 1, 0.109, 0.063, 30.202, 30.483, 277.083, 483.857}, > > { 2, 0.421, 0.11, 30.42, 30.17, 72.2565, 274.273}, > > { 3, 0.452, 0.156, 31.528, 31.325, 69.7522, 200.801}, > > {10, 5.366, 5.382, 42.448, 42.682, 7.91055, 7.93051} > > } > > > Even if we compare only the first calls the range of the snail factor > > goes up to 277 at m = 1, is 72 for m = 2, and is still close to 8 f= or > > larger m. > > > This is my story in other words: I own a very old car, and have > > considered for a long time to change to a newer one - although it > > still can go at 200 km/h on the Autobahn. > > So now I am proud owner of the new brilliant car, and I must learn the > > on important tours (m=1) =EDts maximum speed turns out to be less t= han 1 > > km/h, about 3 km/h (m=2) or at most about 30 km/h. Who laughes? Me > > not! Obviously I'll definitely keep the old car! > > > Ok, maybe I have chosen the wrong example (though in other test runs a > > similar pictures emerged and this example is just the type I'm using > > Mathematica for). Are there perhaps acknowleged benchmarks for such a > > comparison of versions? > > > Finally, dear group, as you might have noticed, I'm asking for > > consolation. Please comment and give me useful hints. Many thanks in > > advance. > > It is a good idea, to split seaching solutions and simplifying the > solutions. In this very special case the indefinite integrals produce > series of hypergeometric functions of n terms in 1/10 of a second. > > And now vs 8 Simplifies this rather trival result for the definite case > on {t,0,oo} into sums of polygammas. > > Of course, nobody can foresee the results of additional simplification > rules in case of special algebraic expressions. This happens with each > new version. More simplification rules, more time. > > My hope is that Wolfram at some point may give much more open control > over implicit function simplification to his mathematical skilled users. > > This is already a problem in trigonometric simpilfications. A simple > body of explicit rules choosen from the appropriate chapters of a > standard formula website would be much more usable than the obscure > dependency on an universal body of rules and an algorithm depending on > time and leafcount. I completely stopped using Sin&Co and I am now > writing all formulas in sin and cos and 1/sin and feed the > simplification rules by hand. Saves hours of computation time. > > The same is true for the superflous work that has to be done in order to > get an expression grouped in a conventional way readable for Mathematica > non-experts. > > -- > > Roland Franzius > > The problem is not the simplification but the basic calculation of an integral. Here are two striking examples: Example 1 ~~~~~~~~~ v 8 Timing[Integrate[n*t*Exp[(-n)*t]*(Exp[t] - 1)^(n - 1), {t, 0, Infinity}]] {30.840999999999994, ConditionalExpression[HarmonicNumber[n], Re[n] > -1]} v 5.2: Timing[Integrate[n*t*Exp[(-n)*t]*(Exp[t] - 1)^(n - 1), {t, 0, Infinity}]] {0.53*Second, n*If[Re[n] > -1, HarmonicNumber[n]/n, Integrate[((-1 + E^t)^(-1 + n)*t)/E^(n*t), {t, 0, Infinity}, Assumptions -> Re[n] <= -1]]} Snail factor s = 30.8/0.53 ~= 60 Example 2 ~~~~~~~~~ v 8 without Simplify Timing[f = Integrate[Log[Abs[(Tan[x] + Sqrt[7])/(Tan[x] - Sqrt[7])]], {x, Pi/3, Pi/2}]] {656.4209999999998, Integrate[Log[Abs[(Sqrt[7] + Tan[x])/(-Sqrt[7] + Tan[x])]], {x, Pi/3, Pi/2}]} No result at all in more than 10 minutes! Therefore I tried FullSimplify in order to get at least a result. v 8 with FullSimplify Timing[f = FullSimplify[Integrate[ Log[Abs[(Tan[x] + Sqrt[7])/(Tan[x] - Sqrt[7])]], {x, Pi/3, Pi/2}]]] Out[1]= {3191.391, Integrate[Log[Abs[(Sqrt[7] + Tan[x])/(Sqrt[7] - Tan[x])]], {x, Pi/3, Pi/2}]} Again, no result, but now it took almost 1 hour of "thinking". Now v 5.2 Timing[f = FullSimplify[Integrate[ Log[Abs[(Tan[x] + Sqrt[7])/(Tan[x] - Sqrt[7])]], {x, Pi/3, Pi/ 2}]]] {32.667*Second, (1*(-9*ArcCot[Sqrt[7]]*Log[2] - (Pi - 6*ArcCot[Sqrt[7]])* Log[-Sqrt[3] + Sqrt[7]] + Pi*Log[Sqrt[3] + Sqrt[7]] + 3*I*(-PolyLog[2, (-Sqrt[3] + Sqrt[7])/(-I + Sqrt[7])] + PolyLog[2, (-Sqrt[3] + Sqrt[7])/(I + Sqrt[7])] + PolyLog[2, (-I + Sqrt[7])/(Sqrt[3] + Sqrt[7])] - PolyLog[2, (I + Sqrt[7])/(Sqrt[3] + Sqrt[7])])))/6} Oops, half a minute and here we are with the result ! Snail factor s = oo (because no solution was found) or s = 3191/32.7 ~= 100 (if we count the times of "absense" for v8). Is it exagerated to speak of a disaster? Regards, Wolfgang

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