Failure in one cohomology code

[stevelinton]

I stumbled across this while playing with some matrix groups. h here is in fact $2S_5$ in a highly redundant permutation representation on 720 points.

Observed behaviour

gap> Print(gg);
[ (), (  1,663,693,517,239,374, 87,519,292, 67)(  2,204,610,299,289,109,499,113,483,462)(  3,341,334,405,136, 73, 41,276,377,314)
    (  4,515,612,128,141,153,269,493,209,241)(  5, 93,127,571,221,110,133,674,668,609)(  6,236,162,506,316,212, 94,671,353,100)
    (  7,114,345,484, 50,213,206,208,527, 55)(  8,455,280,522,277, 83,473,329,513,516)(  9,257, 11,617,503,154,340,283,116,106)
    ( 10,502, 46,689,264,282,258,295,662,525)( 12,520,649,694,416,284,125,654,650,645)( 13,190,310, 25,324,121,410,267,467, 40)
    ( 14,678,646,279,352,214,676,703,180,505)( 15,528,359,656,315, 32,243,177,251, 47)( 16,569,542,144, 26,370,675,219,287,468)
    ( 17, 48,658,343,220,371, 24,686,575,458)( 18, 60,103,620,354,372,244,481,532, 89)( 19,187,297,231,197,373,255,622,705,320)
    ( 20,632,337,131, 57,171,634,712,579,541)( 21,415,490,464, 35, 23,266,625,303,375)( 22,358, 85, 69,707,285,182,509,386,698)
    ( 27,265,529,203, 98,438,414,246,308,173)( 28,181,552,628,605,469,355, 80,300,290)( 29,242,472,296,401,169,142,351,496,339)
    ( 30, 63,149,312, 92,122,170,159, 65,500)( 31,250,210,618,456,238,426,247,118,474)( 33,562,564,687,440, 36,598,603,281,322)
    ( 34,706,349,616,487,366,633,164,115,711)( 37,514,720,523,535, 72,614,518,647,195)( 38,140,539,391,441,459,453,156,685,501)
    ( 39,101,696,691,581,550,317,335,695,530)( 42,383,548,394,286,120,624,425,641,309)( 43,256,201,396,419,235,188,382,546,660)
    ( 44,427,211,507,130, 84,199,640,450,272)( 45,191,301,708,222,172,137,422,710,207)( 49,511,709,714,417, 54,346,684,589, 61)
    ( 51,554,384,104,606,463,536,700,477, 58)( 52,135,362, 76,260,470,313,639,543,421)( 53,454,590, 70,409,471,249, 86,411,189)
    ( 56,533,701,160,185,108,175,635,278,232)( 59,273,406,387,380,615,126,268,567,418)( 62,432,594,717,327,439,435,651,683,600)
    ( 64,630,479,498,408,311,627,489,437, 97)( 66,460,331,488,259,123,274,466,482,150)( 68,215,572,407,323,240,233,224, 96,599)
    ( 71,325,451,398,390,412, 90,524,263,604)( 74,580,588,587,457, 81,124,652,364,475)( 75,413,673,619,679, 82,145,166,420,385)
    ( 77,165,576,119,557,544,193,152,111,478)( 78,644,270,217,399,551,602,129,200,223)( 79,607,486,531,442,446,623,621,497,138)
    ( 88,570,586,578,237,549,667,592,452, 95)( 91,342,168,218,253,508,245,155,365,431)( 99,428,445,271,167,174,205,400,288,132)
    (102,423,376,248,275,318,369,404,368,574)(105,643,202,146,348,344,184,176,403,306)(107,194,361,321,448,504,304,534,198,326)
    (112,584,430,595,328,608,670,716,183,192)(117,629,669,692,593,447,657,392,433,682)(134,461,148,642,360,186,157,381,226,332)
    (139,147,252,492,626,229,402,688,611,491)(143,699,591,367,449,333,521,655,228,553)(151,389,302,690,702,179,597,719,718,636)
    (158,161,596,357,216,540,495,638,379,234)(163,664,395,681,601,672,559,545,680,510)(178,319,582,350,573,443,196,661,494,526)
    (225,436,330,424,566,561,476,465,547,560)(227,393,637,291,480,704,558,298,577,631)(230,434,363,254,677,261,585,429,307,697)
    (262,613,653,565,378,397,512,648,388,356)(293,538,485,305,715,665,556,659,347,713)(294,338,583,563,555,666,336,444,568,537), 
  (  1,175,715,556,160,374,533,713,538,278)(  2, 21,535, 72, 35,109, 23,195, 37,375)(  3,313,192,103,297, 73,135,328,481,622)
    (  4,466,482,141,295,153,331,488,241, 46)(  5,587, 93,301,708,110,364,133,422,710)(  6,610,299,316,720,212,113,483,100,518)
    (  7,357, 28,505,454,213,379,469,352,249)(  8,292,659,347,693, 83,517,485,305,519)(  9,692,257, 77,165,154,433,340,544,193)
    ( 10,294, 66,338,264,282,666,123,336,525)( 11,392,682,106,177,283,669,593,503,359)( 12,494,474,144,179,284,350,456,287,151)
    ( 13,649,173,477,247,121,654, 98,104,210)( 14,605,451,626,445,214,290,524,491,400)( 15,117,629,315,119, 32,447,657, 47,111)
    ( 16,531,262,650, 40,370,497,397,694,324)( 17,112, 52,615,510,371,608,470, 59,601)( 18,553, 76, 63,658,372,449,543,170,686)
    ( 19,591,670,458,291,373,655,584,220,577)( 20, 70,194,530,495,171,411,304,581,161)( 22,627,472,423,679,285,630,351,369,385)
    ( 24,681,465,705, 60, 48,680,330,231,244)( 25,178,463,199,569,467,443, 51,427,675)( 26,618,700,184,138,468,118,384,643,442)
    ( 27,125,636, 79,105,438,520,702,446,344)( 29,148,509,156,709,169,381, 85,539,684)( 30,268,561,480,343,122,406,225,631,575)
    ( 31,582,265,306,130,238,661,414,348,272)( 33,703,634,158,412, 36,646,632,540, 71)( 34,188,548,394, 43,366,256,425,641,235)
    ( 38, 97,360,413,602,459,408,332,145,644)( 39,504,174,562,390,550,107, 99,598,604)( 41,255,298,163,418,341,187,637,672,380)
    ( 42,431,164,115,218,120,253,349,616,365)( 44,403,388,597,219, 84,146,565,389,542)( 45,363, 74,580,585,172,429, 81,124,434)
    ( 49,489,707,200,327, 54,479,698,217,600)( 50,198,139,325,234, 55,321,229, 90,216)( 53,288,492,696,206,471,271,611,335,114)
    ( 56,329,513,185,293,108,280,522,232,665)( 57,552,603,167,189,541, 80,564,132,409)( 58,203,613,621,211,606,308,512,486,640)
    ( 61, 95,275,134,437,417,237,574,186,498)( 62,129, 82,318,578,439,270, 75,102,452)( 64,441,432,586,496,311,501,435,592,296)
    ( 65,559,558,532,183,312,664,393,620,595)( 67,277,473, 87,635,239,516,455,663,701)( 68,594,685,358,619,240,651,391,182,420)
    ( 69,461,368,407,223,386,157,248, 96,399)( 78,224, 88,714,140,551,572,549,589,453)( 86,180,440,402,534,590,279,322,147,361)
    ( 89,227,566,377,143,354,704,560,405,333)( 91,286,624,155,546,508,309,383,168,396)( 92,430,699,334,387,500,716,521,276,567)
    ( 94,614,647,506,490,236,514,523,353,625)(101,398,300,131,208,317,263,628,579,345)(116,528,576,557,251,617,243,152,478,656)
    (126,260,367,197,476,273,421,228,320,436)(127,652,475,609,697,674,588,457,221,677)(128,568,515,258,662,209,563,269,502,689)
    (136,424,395,159,362,314,547,545,149,639)(137,230,571,307,207,191,261,668,254,222)(142,346,683,599,404,242,511,717,323,376)
    (150,460,555,612,583,259,274,537,493,444)(162,266,462,204,464,671,415,289,499,303)(166,642,401,570,215,673,226,339,667,233)
    (176,554,526,416,356,202,536,573,645,378)(181,638,691,688,281,355,596,695,252,687)(190,426,450,623,718,410,250,507,607,690)
    (196,310,719,653,246,319,267,302,648,529)(201,711,706,660,342,382,487,633,419,245)(205,326,527,712,678,428,448,484,337,676), 
  (  1,295,635, 66,374, 46,701,123)(  2,359,720,617,109,177,518,116)(  3,198,575,552, 73,321,343, 80)(  4,473,666,713,153,455,294,715)
    (  5,309,363,633,110,286,429,706)(  6,557,375,669,212,478, 35,392)(  7,380,562,372,213,418,598, 18)(  8,563,665,493, 83,568,293,612)
    (  9,289, 15,647,154,462, 32,523)( 10,278,466,239,282,160,331, 67)( 11,483,251,535,283,299,656,195)( 12,453,640,423,284,140,211,369)
    ( 13,332,146,717,121,360,403,683)( 14,395,530,655,214,545,581,591)( 16,684,265, 82,370,709,414, 75)( 17,355,405,326,371,181,377,448)
    ( 19,524,159,411,373,451,149, 70)( 20,584,491,547,171,670,626,424)( 21,682,316,576, 23,593,100,152)( 22,350,549,621,285,494, 88,486)
    ( 24,300,276,534, 48,628,334,361)( 25,134,105,594,467,186,344,651)( 26, 54,246,166,468, 49,529,673)( 27,420,675, 61,438,619,569,417)
    ( 28,341,504,686,469, 41,107,658)( 29,238,129,262,169, 31,270,397)( 30,189,297,325,122,409,622, 90)( 33,532,206,126, 36,620,114,273)
    ( 34,571, 42,697,366,668,120,677)( 37,106,113,528, 72,503,610,243)( 38, 84,404,654,459, 44,376,649)( 39,449,352,163,550,553,505,672)
    ( 40,148,348, 62,324,381,306,439)( 43,207,253,475,235,222,431,457)( 45,342,364,546,172,245,587,396)( 47,514,340,499,315,614,257,204)
    ( 50,406,603,481, 55,268,564,103)( 51,437,702, 68,463,498,636,240)( 52,638,704,428,470,596,227,205)( 53,320, 71, 65,471,197,412,312)
    ( 56,460,693,502,108,274,519,258)( 57,192,229,225,541,328,139,561)( 58,630,179,224,606,627,151,572)( 59,687, 89,484,615,281,354,527)
    ( 60,208,387,440,244,345,567,322)( 63,249,187,390,170,454,255,604)( 64,718, 96,554,311,690,407,536)( 69,573,586,623,386,526,592,607)
    ( 74,201,708,168, 81,382,710,155)( 76,379,637, 99,543,357,298,174)( 77,415,657,506,544,266,629,353)( 78,613,472,474,551,512,351,456)
    ( 79,182,443, 95,446,358,178,237)( 85,661,578,531,509,582,452,497)( 86,705,398,500,590,231,263, 92)( 87,525,533,482,663,264,175,488)
    ( 91,580,660,301,508,124,419,422)( 93,624,434,711,133,383,585,487)( 94,193,464,117,236,165,303,447)( 97,389,599,477,408,597,323,104)
    ( 98,145,542,511,173,413,219,346)(101,699,279,681,317,521,180,680)(102,650,539,272,318,694,156,130)(111,625,433,671,119,490,692,162)
    (112,252,560,337,608,688,566,712)(115,609,548,254,616,221,425,307)(118,200,648,401,618,217,653,339)(125,685,427,574,520,391,199,275)
    (127,394,230,349,674,641,261,164)(128,329,583,347,209,280,444,305)(131,430,402,465,579,716,147,330)(132,135,216,480,167,313,234,631)
    (136,304,220,605,314,194,458,290)(137,218,588,188,191,365,652,256)(138,698,196,667,442,707,319,570)(141,277,338,538,241,516,336,556)
    (142,247,644,388,242,210,602,565)(143,676,601,691,333,678,510,695)(144,589,308,679,287,714,203,385)(150,292,689,232,259,517,662,185)
    (157,202,435,410,461,176,432,190)(158,558,288,260,540,393,271,421)(161,291,400,639,495,577,445,362)(183,611,436,634,595,492,476,632)
    (184,327,310,642,643,600,267,226)(215,384,479,302,233,700,489,719)(223,378,296,426,399,356,496,250)(228,646,559,335,367,703,664,696)

gap> h := Group(gg);
<permutation group with 4 generators>
gap> SemidirectDecompositionsOfFiniteGroup(h,"str");
Error, List Element: <list>[693] must have an assigned value in
  if H.translabels[img[i]] = depth then
    if mode = 'd' then
        return depth - 1;
    fi;
    e := RelativeOrders( pcgs )[depth - 1];
    i := img[i];
    repeat
        e := e - 1;
        i := i ^ gen;
    until H.translabels[i] <> depth;
    if mode = 'l' then
        return e;
    elif mode = 's' then
        return [ depth - 1, e ];
    fi;
    exp[depth - mindepth] := e;
    g := LeftQuotient( gen ^ e, g );
    bimg := OnTuples( base, g );
fi; at /Users/sal/GIT/gap/lib/pcgsperm.gi:843 called from 
ExponentsOfPcElementPermGroup( pcgs, g, 1, Length( pcgs ), 'e' ) at /Users/sal/GIT/gap/lib/pcgsperm.gi:1254 called from
ExponentsOfPcElement( ocr.modulePcgs, x ) at /Users/sal/GIT/gap/lib/onecohom.gi:264 called from
ocr.moduleMap( n ) at /Users/sal/GIT/gap/lib/onecohom.gi:1037 called from
OCEquationVector( ocr, rels[i] ) at /Users/sal/GIT/gap/lib/onecohom.gi:1247 called from
OCOneCocycles( ocr, true ); at /Users/sal/GIT/gap/lib/grpcompl.gi:142 called from
...  at *stdin*:143
type 'quit;' to quit to outer loop
brk> Where(30);
ExponentsOfPcElementPermGroup( pcgs, g, 1, Length( pcgs ), 'e' ) at /Users/sal/GIT/gap/lib/pcgsperm.gi:1254 called from
ExponentsOfPcElement( ocr.modulePcgs, x ) at /Users/sal/GIT/gap/lib/onecohom.gi:264 called from
ocr.moduleMap( n ) at /Users/sal/GIT/gap/lib/onecohom.gi:1037 called from
OCEquationVector( ocr, rels[i] ) at /Users/sal/GIT/gap/lib/onecohom.gi:1247 called from
OCOneCocycles( ocr, true ); at /Users/sal/GIT/gap/lib/grpcompl.gi:142 called from
ComplementClassesRepresentativesSolvableNC( G, N ) at /Users/sal/GIT/gap/lib/grppccom.gi:1191 called from
ComplementClassesRepresentatives( G, N ) at /Users/sal/GIT/gap/lib/grpnames.gi:831 called from
<function "SemidirectDecompositionsOfFiniteGroup">( <arguments> )
 called from read-eval loop at *errin*:1
brk> 
gap> 

Expected behaviour

The calculation should work.

Copy and paste GAP banner (to tell us about your setup)

┌───────┐   GAP 4.10dev-2113-gf7f36d7 of today
 │  GAP  │   https://www.gap-system.org
 └───────┘   Architecture: x86_64-apple-darwin18.5.0-default64-kv6
 Configuration:  gmp 6.1.2, GASMAN
 Loading the library and packages ...
Syntax warning: Unbound global variable in /Users/sal/GIT/gap/pkg/atlasrep/gap/utils.gi:44
        pos:= POSITION_FIRST_COMPONENT_SORTED( WidthUnicodeTable, ints[j] );
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 Packages:   AClib 1.3.1, Alnuth 3.1.0, AtlasRep 1.5.1, AutoDoc 2019.02.22, AutPGrp 1.10, CRISP 1.4.4, Cryst 4.1.18, CrystCat 1.1.8, 
             CTblLib 1.2.2, FactInt 1.6.2, FGA 1.4.0, GAPDoc 1.6.2, IRREDSOL 1.4, LAGUNA 3.9.2, Polenta 1.3.8, Polycyclic 2.14, 
             PrimGrp 3.3.2, RadiRoot 2.8, ResClasses 4.7.1, SmallGrp 1.3, Sophus 1.24, SpinSym 1.5, TomLib 1.2.7, TransGrp 2.0.4, utils 0.61
             
 Try '??help' for help. See also '?copyright', '?cite' and '?authors'

[fingolfin]

@stevelinton that input gg seems to be truncated, so we have no way to reproduce it. Perhaps you could put the full gg into a .txt file and attach that to the issue?

[stevelinton]

gg.txt

[hulpke]

This looks suspiciously like #3496.
As I cannot reproduce it in my working version, i suggest testing again after #3508 has been merged.

[wilfwilson]

Note that #3508 is now merged

[stevelinton]

#3508 appears to have fixed this.