# [R] prod and F90 product

Filippo ingfimo at gmail.com
Fri Nov 8 00:39:54 CET 2013

```Hi,
I'm having strange differences between the R function prod ad the F90
function product.
Processing the same vector C (see attachment). I get 2 different results:
prod(C) = 1.069678e-307
testProduct(C) = 0

where testProd is the following wrapping function:

testProd <- function(x) {
return(.Fortran('testProd', as.double(x), as.double(0),
as.double(0), as.integer(length(x))))
}

subroutine testProd(x, p, q,  n)
implicit none
integer, intent (in) :: n
double precision, intent (in) :: x(n)
double precision, intent (out) :: p
double precision, intent (out) :: q
integer :: i

p = product(x)
q=1
do i = 1, n
q = q*x(i)
end do
end subroutine testProd

I check the lowest possible number and seems to be the same for both R
and F90.
Can anyone help me understanding this behaviour?
Regards,
Filippo

-------------- next part --------------
c(0.126667774727727, 0.126778508335206, 0.126889731437094, 0.127001445486345,
0.127113651944097, 0.127226352279715, 0.127339547970833, 0.127453240503398,
0.127567431371714, 0.127682122078482, 0.127797314134848, 0.127913009060448,
0.128029208383447, 0.128145913640589, 0.128263126377241, 0.128380848147438,
0.128499080513928, 0.128617825048222, 0.128737083330636, 0.128856856950339,
0.128977147505404, 0.129097956602849, 0.129219285858691, 0.129341136897992,
0.129463511354905, 0.129586410872726, 0.129709837103945, 0.12983379171029,
0.129958276362782, 0.130083292741782, 0.130208842537045, 0.130334927447768,
0.130461549182643, 0.130588709459909, 0.130716410007402, 0.130844652562612,
0.130973438872731, 0.13110277069471, 0.131232649795309, 0.131363077951156,
0.131494056948797, 0.131625588584752, 0.131757674665574, 0.131890317007896,
0.132023517438499, 0.132157277794358, 0.132291599922703, 0.132426485681077,
0.132561936937394, 0.132697955569994, 0.132834543467704, 0.132971702529897,
0.133109434666551, 0.133247741798307, 0.133386625856532, 0.13352608878338,
0.133666132531848, 0.133806759065846, 0.133947970360249, 0.134089768400969,
0.134232155185011, 0.134375132720541, 0.134518703026945, 0.1346628681349,
0.13480763008643, 0.134952990934981, 0.135098952745478, 0.135245517594397,
0.13539268756983, 0.13554046477155, 0.135688851311081, 0.135837849311768,
0.13598746090884, 0.136137688249485, 0.136288533492915, 0.13643999881044,
0.136592086385536, 0.136744798413917, 0.136898137103608, 0.137052104675016,
0.137206703361001, 0.137361935406953, 0.137517803070863, 0.137674308623401,
0.137831454347986, 0.137989242540865, 0.138147675511187, 0.138306755581082,
0.138466485085736, 0.13862686637347, 0.13878790180582, 0.138949593757609,
0.139111944617036, 0.13927495678575, 0.139438632678933, 0.139602974725378,
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0.149335454568934, 0.149539788124169, 0.149744945041738, 0.149950928663571,
0.150157742351019, 0.150365389484985, 0.150573873466047, 0.150783197714589,
0.150993365670932, 0.151204380795458, 0.151416246568747, 0.15162896649171,
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0.156299816845904, 0.15653225668127, 0.156765637118446, 0.156999962188775,
0.157235235947601, 0.15747146247443, 0.157708645873097, 0.157946790271927,
0.158185899823904, 0.158425978706841, 0.158667031123545, 0.158909061301989,
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0.17953974567201, 0.179867895909293, 0.180197427497096, 0.180528347202073,
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0.187810778081621, 0.188174040309841, 0.18853885903537, 0.188905242169644,
0.189273197676518, 0.189642733572677, 0.190013857928047, 0.19038657886621,
0.190760904564824, 0.191136843256045, 0.191514403226953, 0.191893592819983,
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0.193814281032235, 0.194203426704341, 0.194594261982594, 0.19498679566826,
0.195381036622021, 0.195776993764442, 0.196174676076453, 0.196574092599828,
0.196975252437666, 0.197378164754889, 0.197782838778727, 0.198189283799226,
0.198597509169745, 0.199007524307466, 0.199419338693909, 0.19983296187545,
0.20024840346384, 0.200665673136737, 0.201084780638235, 0.201505735779406,
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0.23798644302494, 0.238576908208741, 0.239170195648803, 0.239766322299235,
0.240365305243027, 0.24096716169322, 0.241571908994073, 0.242179564622251,
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0.245262088776728, 0.245887568946107, 0.246516083589072, 0.24714765128574,
0.247782290759884, 0.248420020880245, 0.249060860661866, 0.24970482926744,
0.25035194600866, 0.251002230347604, 0.251655701898113, 0.252312380427204,
0.252972285856481, 0.253635438263571, 0.254301857883574, 0.254971565110527,
0.255644580498884, 0.256320924765013, 0.257000618788707, 0.257683683614715,
0.258370140454285, 0.259060010686729, 0.259753315861001, 0.260450077697291,
0.261150318088643, 0.261854059102583, 0.262561322982772, 0.263272132150668,
0.263986509207217, 0.264704476934552, 0.265426058297719, 0.26615127644642,
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0.353447024234028, 0.354651493544003, 0.355862987674435, 0.357081559690603,
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0.363282480505872, 0.36454466247991, 0.36581430805203, 0.367091474429409,
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0.579158900331789, 0.581867414167945, 0.584596034473331, 0.587344954980342,
0.590114371702885, 0.592904482967725, 0.595715489446323, 0.59854759418716,
0.601401002648568, 0.604275922732072, 0.607172564816249, 0.610091141791118,
0.613031869093063, 0.615994964740309, 0.618980649368945, 0.621989146269524,
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0.821096643412089, 0.825759717056535, 0.830463339610946, 0.835207964270926,
0.839994050316449, 0.844822063204971, 0.849692474666098, 0.854605762797835,
0.85956241216442, 0.864562913895808, 0.869607765788795, 0.874697472409829,
0.879832545199546, 0.885013502579025, 0.890240870057837, 0.895515180343878,
0.900836973455035, 0.906206796832719, 0.911625205457281, 0.917092761965356,
0.922610036769158, 0.928177608177759, 0.933796062520393, 0.939465994271806,
0.945188006179693, 0.950962709394249, 0.956790723599879, 0.962672677149092,
0.968609207198612, 0.974600959847752, 0.98064859027908, 0.986752762901407,
0.992914151495149, 0.999133439360083, 1.00541131946554, 1.0117484946031,
1.01814567754173, 1.02460359118558, 1.03112296873426, 1.03770455384584,
1.04434910080242, 1.05105737467852, 1.05783015151208, 1.06466821847839,
1.07157237406671, 1.07854342825986, 1.08558220271664, 1.09268953095722,
1.09986625855153, 1.10711324331065, 1.11443135548128, 1.12182147794325,
1.12928450641032, 1.13682134963396, 1.14443292961054, 1.15212018179164,
1.15988405529777, 1.16772551313532, 1.17564553241696, 1.18364510458546,
1.19172523564088, 1.19988694637132, 1.20813127258717, 1.21645926535893,
1.22487199125854, 1.23337053260447, 1.24195598771034, 1.25062947113729,
1.25939211395004, 1.2682450639767, 1.27718948607235, 1.28622656238638,
1.29535749263372, 1.3045834943698, 1.31390580326946, 1.32332567340966,
1.33284437755611, 1.34246320745381, 1.35218347412142, 1.36200650814963,
1.37193366000337, 1.38196630032797, 1.39210582025918, 1.40235363173713,
1.41271116782414, 1.4231798830264, 1.43376125361948, 1.44445677797766,
1.45526797690703, 1.46619639398233, 1.47724359588748, 1.48841117275974,
1.49970073853747, 1.51111393131137, 1.5226524136792, 1.53431787310381,
1.54611202227448, 1.55803659947138, 1.57009336893313, 1.58228412122724,
1.59461067362338, 1.60707487046933, 1.61967858356934, 1.63242371256497,
1.64531218531793, 1.65834595829495, 1.67152701695441, 1.68485737613442,
1.69833908044218, 1.71197420464445, 1.72576485405856, 1.73971316494402,
1.7538213048941, 1.76809147322728, 1.78252590137798, 1.79712685328638,
1.8118966257868, 1.82683754899417, 1.84195198668824, 1.85724233669495,
1.87271103126437, 1.88836053744482, 1.90419335745236, 1.92021202903522,
1.93641912583231, 1.95281725772524, 1.96940907118308, 1.9861972495989,
2.00318451361754, 2.02037362145344, 2.03776736919778, 2.0553685911138,
2.07318015991939, 2.09120498705573, 2.10944602294091, 2.12790625720719,
2.14658871892075, 2.16549647678244, 2.18463263930821, 2.20400035498756,
2.22360281241868, 2.24344324041827, 2.26352490810464, 2.28385112495197,
2.30442524081398, 2.32525064591489, 2.34633077080554, 2.36766908628253,
2.38926910326789, 2.41113437264693, 2.43326848506172, 2.45567507065736,
2.47835779877839, 2.50132037761223, 2.52456655377673, 2.54810011184839,
2.57192487382806, 2.59604469854048, 2.62046348096394, 2.64518515148636,
2.67021367508358, 2.69555305041579, 2.72120730883764, 2.74718051331758,
2.77347675726154, 2.80010016323613, 2.82705488158604, 2.85434508894054,
2.88197498660324, 2.90994879881949, 2.93827077091539, 2.96694516730204,
2.99597626933882, 3.02536837304872, 3.05512578667895, 3.08525282809956,
3.1157538220327, 3.1466330971048, 3.17789498271367, 3.20954380570253,
3.24158388683228, 3.27401953704356, 3.30685505349945, 3.34009471539983,
3.37374277955779, 3.40780347572854, 3.44228100168088, 3.47717951800111,
3.51250314261899, 3.54825594504538, 3.58444194031052, 3.62106508259244,
3.65812925852402, 3.69563828016792, 3.73359587764766, 3.77200569142381,
3.81087126420363, 3.85019603247277, 3.88998331763749, 3.93023631676615,
3.9709580929185, 4.01215156505172, 4.05381949749217, 4.09596448896233,
4.13858896115228, 4.18169514682602, 4.225285077453, 4.26936057035584,
4.31392321536612, 4.35897436098048, 4.40451510001032, 4.45054625471939,
4.49706836144439, 4.54408165469509, 4.59158605073174, 4.63958113061874,
4.68806612275574, 4.73703988488826, 4.78650088560256, 4.83644718531116,
4.88687641673778, 4.93778576491282, 4.9891719466933, 5.04103118982387,
5.09335921155849, 5.14615119686566, 5.19940177624365, 5.25310500317552,
5.30725433125797, 5.36184259104187, 5.41686196662666, 5.47230397205558,
5.5281594275631, 5.58441843573103, 5.64107035761498, 5.69810378890798,
5.75550653621385, 5.81326559350816, 5.87136711887098, 5.92979641158084,
5.98853788966604, 6.04757506801486, 6.10689053715278, 6.16646594280064,
6.22628196633371, 6.28631830626767, 6.34655366090301, 6.40696571226526,
6.46753111148334, 6.52822546575354, 6.58902332704112, 6.6498981826754,
6.71082244799802, 6.7717674612266, 6.83270348069849, 6.89359968466034,
6.95442417377007, 7.01514397647684, 7.0757250574436, 7.13613232917356,
7.19632966699837, 7.25627992758037, 7.31594497107456, 7.37528568708809,
7.43426202456508, 7.49283302571387, 7.55095686408033, 7.60859088685726,
7.66569166150283, 7.72221502672414, 7.77811614786189, 7.83334957669142,
7.88786931563279, 7.94162888633836, 7.99458140260103, 8.04667964749941,
8.09787615466862, 8.14812329355627, 8.19737335849394, 8.2455786613843,
8.29269162777338, 8.33866489604749, 8.38345141946338, 8.42700457069126,
8.46927824852053, 8.51022698635093, 8.54980606206488, 8.58797160885252,
8.62468072653814, 8.65989159293669, 8.69356357475138, 8.7256573375091,
8.75613495401908, 8.7849600108323, 8.8120977121755, 8.83751498083311,
8.86118055545461, 8.88306508377275, 8.90314121123023, 8.92138366452907,
8.93776932963719, 8.95227732381165, 8.96488906122628, 8.97558831182403,
8.98436125304979, 8.99119651415869, 8.99608521283661, 8.99902098391393
)
```