How to find the location of approximately equal value in vector?

Question

vinod kumar govindu 2017-2-3

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/323163-how-to-find-the-location-of-approximately-equal-value-in-vector

评论： Walter Roberson 2017-2-10

采纳的回答： Stephen23

在 MATLAB Online 中打开

I having Z =10.7000 and ACF(auto correlation function)

ACF =

Columns 1 through 6
         0   -1.0000   -1.8478   -2.2678   -2.0719   -1.2071
Columns 7 through 12
    0.2242    1.9749    3.6955    5.0000    5.5433    5.0962
Columns 13 through 18
    3.6027    1.2071   -1.7549   -4.8033   -7.3910   -9.0000
Columns 19 through 24
   -9.2388   -7.9246   -5.1334   -1.2071    3.2856    7.6317
Columns 25 through 30
   11.0866   13.0000   12.9343   10.7530    6.6641    1.2071

here i want to find out approximately equal value of Z in ACF and also location of the ACF value. Here the Z value is approximately equal to 10.7530 of ACF and it present at location of ACF(28). Help me to write the code for find approximately equal value of Z in ACF and its location(28).

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Stephen23 2017-2-3

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/323163-how-to-find-the-location-of-approximately-equal-value-in-vector#answer_253168

编辑：Stephen23 2017-2-3

在 MATLAB Online 中打开

You should calculate the absolute differences, and then use min to get the closest value:

 >> Z = 10.7000;
 >> ACF = [0,-1.0000,-1.8478,-2.2678,-2.0719,-1.2071,0.2242,1.9749,3.6955,5.0000,5.5433,5.0962,3.6027,1.2071,-1.7549,-4.8033,-7.3910,-9.0000,-9.2388,-7.9246,-5.1334,-1.2071,3.2856,7.6317,11.0866,13.0000,12.9343,10.7530,6.6641,1.2071]
 >> [~,idx] = min(abs(Z-ACF))
 idx =
        28
 >> out = ACF(idx)
 out =  10.753

13 个评论
显示 11更早的评论隐藏 11更早的评论

Walter Roberson 2017-2-7

在 MATLAB Online 中打开

The code Stephen had,

[~,idx] = min(abs(Z-ACF))

finds the index where the scalar Z is closest to one of the values in the full vector ACF.

Suppose you wanted to skip the first entry in ACF, then you could use

[~,idx] = min(abs(Z-ACF(2:end)))

then an index value output of 1 would mean the first position relative to ACF(2:end), so if you want to know the position relative to the entire ACF array, you have to add 1 -- the difference between the starting point of 2 and the typical starting point of 1.

Just the same way, if you want to search only ACF(25:end) you can use

[~,idx] = min(abs(Z-ACF(25:end));

and now an idx value of 1 would correspond to the beginning of ACF(25:end). If you wanted to know the location relative to all of ACF, you would have to add 24 to idx -- the difference between the starting point of 25 and the typical starting point of 1.

So the formula to find the location relative to all of ACF becomes

idx + (starting point minus 1)

and I coded it with a variable for the starting point so you could adjust the starting point easily.

vinod kumar govindu 2017-2-10

编辑：Walter Roberson 2017-2-10

在 MATLAB Online 中打开

Dear Walter Roberson ,

here i posted my code my aim is to find out the auto correlation and cross correlation of the given signals x,y,z.

Auto correlation can be done by compare signal x with itself with some delay. cross correlation can be done by compare twp different signals x,y. I attached a picture contains ACF and CCF equations. In that there is mistake in CCF. It is CCF only not CCF(k). ACF(k) is a auto correlation of x(n) with delayed signal x(n-k). I used symsum function for summation but i am getting error. Given below i posted the error which i got while using symsum funtion.

??? Attempted to access IRx1(0); index must be a positive integer or logical.
Error in ==> G12 at 26 ACF1(i,n)=bug+((IRx1(n)+j.*QRx1(n)).*(IRx1(n-i)-j.*QRx1(n-i)));

I dont know it is correct function for the summation of complex signals.

The procedure is to multiply the x(n) with it self by giving delay x(n-k) and add all those to get ACF.

Help me to solve this coding.

    clc;
    close all;
    clear all;
    IRx1=[2.50582817101952,2.41713141145528,1.86841439304153,0.605047602894921,-0.703566724847468,-1.53347690224738,-2.68534618710372,-3.37564979764617,-3.60976457774389,-3.31964450712546,-2.66522613876526,-1.77623560339244,-0.492474329662971,0.160290587013230,0.507220033329129,0.312331782163865,0.113076760989049,-0.510845957116963,-1.02537238124377,-1.54315957923986,-1.92651006745793,-2.07761357141181,-1.96179000520892,-1.61605886905197,-0.998502032475426,-0.606791167516796,-0.408862392930745,-0.721810897897046,-1.03865928287495,-1.67596511911259,-2.17900191449449,-3.22455973533726,-4.20122236827395,-4.88936414084140,-4.98588492090064,-4.64611986699242,-3.89295986195026,-2.85016108345810,-1.51000979182552,-0.114053165824088,1.08073054478529,1.85120398545085,2.05071399629919,1.55713172662244,0.577854501379098,-0.781845566782136,-2.28138320255862,-3.59143240245656,-4.48240785969556,-4.80042560007416,-4.49335459690561,-3.61773210916393,-2.28811421907310,-0.616269087330731,1.34646211479523,2.58576397249433,3.18726452764764,3.55099127809478,3.39245771843159,2.67982568751591,1.28811220734259,0.290545697789977,-1.11083900436137,-2.24846907912449,-3.41008937840863,-4.08132603131973,-4.19202057140981,-3.75598274404288,-2.86511558343952,-1.33166071513922,-0.0888600143436430,1.04383587114973,1.90146530084647,2.36534314627888,2.37807964444616,1.94943719786547,1.15254387997119,0.111265653064370,-1.01930534408229,-2.44869015588492,-3.23965758371861,-3.36628409964266,-3.50424270023697,-3.29456430470408,-2.80531710517118,-2.14315533001624,-1.47170964682503,-0.795233104046106,-0.346629678415243,0.243676163193890,0.0561703047489547,-0.740610277561049,-1.27386267061423,-2.08480520623948,-2.43267440079923,-2.76937121834168,-2.99337398387634,-3.08558943524334,-3.04783986140056,-3.07230565610149,-2.94490942924285,-2.64367433237923,-2.33302680338966,-1.83789598292898,-1.97823772406445,-1.93937035972245,-2.20625565463774,-2.23887113241593,-2.58437228749598,-3.52733915198916,-4.07019344900751,-4.31937286306846,-4.82277220060252,-5.11817728167131,-5.13481364324164,-4.84209660869776,-4.24673283123647,-3.54290123157843,-2.67022083716594,-1.34112096240404,-0.847195923908771,-0.136621642288736,-0.113124944412861,-0.346362291440859,-0.812589735653853,-1.43525740508435,-2.31980008066570,-2.47632619329387];
    IRx2=[1.01460425716151,0.789387892284636,0.465419065393918,-0.270674605261502,-0.324209579543460,-0.786127887110611,-1.31672413476201,-1.68974069580242,-1.68683326153294,-1.91463828346887,-1.99070592373177,-1.86159099936316,-1.51752077197991,-0.954746832721099,-0.209994594029173,0.811346972019044,1.61404780608856,1.96001533542083,2.49485352039829,2.76882719749157,2.73797080108476,2.39139122359568,1.75505098733065,0.892009683076733,0.0815037131794636,-1.01857047035352,-2.02213961753928,-2.93877580921443,-3.23294982923665,-2.99973300999368,-2.91528946965527,-2.01533398528999,-0.768915862561078,0.673940528188069,2.12014743798596,3.07912747337142,4.14769021857149,4.55429333026318,4.33404517081416,3.48728067593388,2.11504461592450,0.408386612077747,-1.37865630550980,-2.93271295825688,-4.10799835209611,-4.78408173369122,-4.46062915666738,-3.45118437406266,-1.90549976700760,-0.0589501797260740,1.80599108593936,3.40640695154048,4.54526003105368,5.18679223295696,5.33036875356390,4.48934454418814,3.04699266357109,1.54593614053326,0.135501358878592,-1.09302611399635,-1.85681416548019,-2.15661323317940,-2.32274156157063,-1.88578807031514,-1.04852785251823,0.0680470909691132,1.28358265681183,2.42637788797044,3.35703514167297,3.64767743571924,3.98742663931683,4.00581733933059,3.73109093230059,3.21309282961231,2.51322792193615,1.69750401007136,0.833207984444164,-0.0116689660343153,-0.768138496031731,-1.55330142621117,-1.97458482357104,-2.15477811425155,-1.87735825878768,-1.21139358892745,-0.236527845717644,0.916737394288882,2.02731175399555,3.11127236571521,3.76594186553903,4.15152292241076,3.65721802838211,2.68922312868832,1.35424397679989,-0.422175665866012,-1.47203008503273,-2.72588745633588,-3.60988696547965,-3.97459918433722,-3.75578630206334,-2.70609884338261,-2.18677889085995,-0.724861849873928,0.705065802834293,1.64916146563410,2.43886933811804,2.42744868507788,1.80584985609909,0.908696622442396,-0.705707238128764,-2.27270189339574,-3.37234227805187,-4.20160175589701,-4.17172206185601,-3.55339005011385,-2.42912689725117,-1.31805658267917,0.239514364570606,1.47991933586132,2.36459637723685,2.56164473359209,2.55384087296497,1.60993379649284,0.629564432592203,-0.645304518556036,-1.97479167479100,-3.10148212130029,-3.80003159784154,-3.94619491777448];
    IRx3=[-0.993128890005284,-1.76594777520882,-2.31949979637286,-2.21870218475863,-2.45080409040613,-2.28219201343847,-1.02229193980455,0.453921919149053,1.90050025467925,2.59193207732919,2.69060034703535,2.15307465169026,1.05521829466591,-0.413379640224464,-2.00515321844758,-3.31946860669385,-4.41984467230870,-5.23501910734096,-5.16606973083684,-4.46543527319935,-3.25160209193610,-1.72671153217760,-0.140190359696800,1.25484213325138,2.02459808250948,2.62069605149156,2.60946644908517,2.09571076461969,1.01910162812756,-0.269202255127129,-1.23809167199613,-2.47193225700054,-3.38135220256387,-3.83434288531237,-3.68937515950887,-3.39741304134523,-2.42972386681567,-1.50374882556885,-0.508048999212305,0.404545935881431,1.10330611589675,1.49838880640620,1.55228571196290,1.34281769078276,0.842640828669976,-0.0527018153170412,-0.713595602532179,-1.26283024770965,-1.61665181987407,-1.72898418633932,-1.59713183999718,-1.26040333662297,-0.752932366670609,-0.0577665529710810,0.374250486357905,0.941611680965764,1.08213296963860,1.27444212679685,1.21015441855056,0.785605530968928,-0.180891381312223,-0.928904425156226,-1.73454047225642,-2.77036791374945,-3.73068718741744,-4.34861858499960,-4.53295554566547,-4.26883529651507,-3.61886401478481,-2.36423308245108,-1.43888043407460,-0.627189322960582,-0.0783446858768140,0.105958148447062,-0.111671539130095,-0.698782517051578,-1.55953435306677,-2.55178800751300,-3.51170697380857,-3.96060456182168,-4.42738941481774,-4.26437253555307,-4.15000793763006,-3.71955395095441,-3.03386608743514,-2.19598516647012,-1.39928527264283,-0.563069421120779,-0.0488066084850562,0.0229426002962217,-0.166071205981264,-0.696044288513010,-1.47745602544096,-2.36416001821257,-3.14726579723785,-4.02850927072230,-4.71723059101617,-5.10569764618782,-5.12914144917017,-4.99809288524002,-3.92091606240318,-3.00656913581731,-1.91111082249582,-0.565619991349472,0.283627761416091,0.947356788212610,0.948578976391194,0.906033103627324,0.165663577711276,-0.528126599095243,-1.75073591909251,-2.76186496190158,-4.01400972532222,-4.97621829735726,-5.52200879346877,-5.24556962852168,-4.80996281212845,-4.17173805622293,-3.24903463733582,-2.23274479585379,-0.979573531993498,0.423167172481398,1.16521650753348,1.49978408672960,1.36002336661019,0.741577094736565,-0.289522665579945,-1.60088092364450];
    QRx1=[-0.144718579660555,0.995946652625673,2.05637645961698,2.61196347518716,3.25632649951836,3.08746302178533,2.45005524983264,1.52879189873049,0.0795600257263762,-0.903503642646553,-1.66384374630175,-2.07219543395580,-1.73663051946867,-1.22493813342171,-0.511968187169972,0.111113406512994,0.796516202647878,0.977755843153328,1.25462033881561,1.24592323194847,0.996209115120566,0.609489969080677,0.223354235342819,-0.0248956407188340,-0.232342453639286,0.174464228212001,0.807619460912736,1.49311646218381,2.21645131610826,2.67054620724355,3.06251300887572,3.09478595401401,2.63306697209545,1.73954071310858,0.532969121848919,-0.652371421489012,-1.45428721135333,-2.28225224335881,-2.60690673920328,-2.34235411873884,-1.51408904246930,-0.255026384528728,1.21922118882082,3.02115178742696,4.10050381643365,4.96903735582075,4.81132933804762,4.04180574992444,2.79181617599615,1.27442184206188,-0.255083903745787,-1.54528645820358,-2.42200036300971,-2.78267604719178,-2.42252639176325,-1.52142442818247,-0.307372780120042,1.16373862378014,2.59566895376017,3.82281007709030,4.68018360704009,5.05114433673019,4.82593849729210,4.20732887404119,3.07060487849618,1.62519161882054,0.0818617642666102,-1.34270890438126,-2.45728108780638,-3.18997435899711,-3.26264000733367,-2.85030338447939,-2.03755274312990,-0.961712703315067,0.208817912882685,1.29975076000225,2.15604845685741,2.66356786203298,2.76429227850948,2.60505351129691,1.84689048244303,0.820028928366605,-0.0623265017645658,-0.862750087599546,-1.46018221335862,-1.77273253255276,-1.73167622697005,-1.53061294715227,-1.07761129848942,-0.782769139847865,0.0264483256493230,0.436887172479494,0.789414211727582,0.727446167963397,0.756415264991138,0.618513152633964,0.393549801823466,0.131886491958235,-0.114912262481089,-0.545127730055126,-0.510377281509120,-0.512557411426055,-0.391659486423605,-0.0710516328225203,0.00509349801989560,0.426987287620363,0.627750665719879,0.943494833829077,1.35343204458950,1.54615610141597,1.51295396896865,1.31529822675633,0.856736949102081,0.198390357042307,-0.569333696382446,-1.32418460730406,-1.92388745351658,-2.45670604169471,-2.70052375902505,-2.08229123921291,-1.73603019307446,-1.13987994071623,-0.474015604873290,0.162399114708555,0.674102061951758,0.524785424561854,0.214556638570243,-0.0938660949699451];
    QRx2=[1.25748821083559,1.59232820540285,1.89211923520759,1.88099181061371,1.75907167934012,1.82428183523391,1.78041254700247,1.56472843457122,1.04088165066503,0.646556290077192,0.128310603656031,-0.450501773794132,-1.00480904530030,-1.45912613104007,-1.72868619330447,-1.91466170173093,-1.52145406181707,-0.744755343783896,0.0164457823216737,0.920124206140120,1.87280368258172,2.76798592075878,3.49740829873187,3.96346095177321,3.92634814268997,3.79047264113801,3.25131401251054,2.19516080475489,1.11866898714991,-0.0868644803222537,-1.15381581692583,-2.08217190852378,-2.65256309571722,-2.74086608851374,-2.13703911177943,-1.86213629706259,-0.179665202068858,1.42353419433705,3.09919520661605,4.59655516335476,5.67777383988329,6.15849489368285,5.94162047977465,5.41655735638638,3.89777136864294,1.75659884543326,-0.147314506470493,-1.80654394943821,-2.97361612236474,-3.47952694704350,-3.26168307461630,-2.37373106741707,-0.986656040212108,0.680993458251602,2.66897460606418,4.14915838268406,5.28633393172347,5.56585128716944,5.32155618820885,4.58001729846046,3.68475979062889,2.18321673024426,0.727376002538077,-0.939867972535359,-2.14028958454835,-2.91210522072983,-3.20882166062459,-3.05352877769973,-2.52510818506159,-1.70592670614687,-0.851669664801974,0.0405071413518816,0.874314119614612,1.57491349902664,2.08961027424417,2.38518328361133,2.44437288087680,2.26371843129368,1.85394131721738,1.59842253507776,0.711185513135204,0.0404410173761393,-1.01883306281697,-1.89543095968338,-2.45170009387046,-2.58418936090662,-2.22354516228131,-1.40250297386122,-0.142751951346500,1.59542559405902,2.93768034088717,4.05373057297677,4.77627132908852,4.82664828257853,4.11455681138587,3.49068770809641,2.43703556765478,1.13299280408855,-0.192807969927715,-1.40172126792556,-1.95224338365755,-2.12390938625579,-1.65547574874616,-0.458219572865563,1.07830126344190,2.51125426751961,4.13485781495850,4.96487384457950,5.32729501591053,5.29550758377778,4.46931759931741,3.02864828865319,1.65029660558493,0.362393361769723,-0.594496557791115,-0.988543113338450,-0.925025563983850,-0.334419146424679,0.716880119341661,1.79250194692824,3.22379242483073,4.31309335618836,5.20263838196125,5.57918860188955,5.35976324760898,4.57171837761737,3.35665430473978,1.92253002265421];
    QRx3=[1.61469434821989,1.28110087283433,0.593981423858839,-0.0746609794962341,-0.891803824646148,-2.19303462998841,-2.62044173173250,-2.33773458592233,-1.14868797987302,0.187752799404550,1.72921097658605,3.20949521901254,4.35189005875512,4.96422758117794,4.93938714967720,4.08414134060692,3.03450684126624,1.89291039683914,0.263892352374029,-1.21185894615126,-2.29786178930600,-2.82730994360425,-2.73002447245140,-2.04185996536298,-0.978459491542767,0.463296101102056,1.96310381648816,3.47769048065473,4.28572284988762,4.48069796806336,4.52430480758476,3.96142604376931,2.96223292698943,1.69588086517021,0.269549938642862,-0.470169450225313,-1.59577743807407,-2.08965359044770,-2.20036578610210,-1.94267300943902,-1.38745944463219,-0.647424702259412,0.142727660186499,0.457263258501747,1.02854810107158,1.53119350556719,1.43704558729807,1.09870604559311,0.589409191167250,0.00703713408324849,-0.542958205090700,-0.965174046229494,-1.21383179950569,-1.26407039195322,-1.25897405515521,-0.681320371584185,0.0334979706460327,0.911813186967266,1.84129800199022,2.67248382949417,3.19578726489379,3.23645876594367,3.35429118367439,3.44781140646502,2.88762169576680,2.01590005115277,1.00015989096743,0.0286399105764878,-0.722354919489267,-1.13763940346719,-1.04553560746135,-0.566614389385489,0.215915010612429,1.16617500935677,2.11970048353193,2.91199894737582,3.40662737197769,3.51802519672367,3.22535601020925,2.36107413812950,1.58191148418807,0.582199081336153,-0.245139894736487,-0.973514153843321,-1.48447989900030,-1.69133925164542,-1.56892560973338,-1.08445968606643,-0.360974609164748,0.496588571825767,1.40302979009760,2.17079631650935,2.67736691587632,3.13836637897697,2.38054122224518,1.97100715599610,1.24885416031121,0.307919228543620,-0.722710835794146,-1.50341250319490,-2.01468520812255,-2.68666490478536,-2.97425216528387,-2.89646892777086,-2.52379881302396,-1.49901796224810,-0.506869568406280,0.907651361053495,1.75345622216872,2.55545782056647,2.90248642844106,2.86882256178575,2.29975359926686,1.31819570586921,0.0578257551530834,-1.35655604583865,-2.53551533399583,-3.45158622002622,-4.07401651828128,-4.52543821838908,-4.36880666597097,-3.47644873119799,-2.46651478664132,-1.22740964353534,0.0764465476581728,1.26339866951640,2.15988323096008,2.61759542869763];
    %IRx and QRx are inphase and quadrature phase signals
    x=IRx1+j*QRx1;%IRx1 is inphase signal and QRx1 is quadrature phase
    y=IRx2+j*QRx2;
    z=IRx3+j*QRx3;
    for i=1:128
            j=sqrt(-1);
            syms IRx1 QRx1
            ACF1(i)=symsum((IRx1(n)+j.*QRx1(n)).*(IRx1(n-i)-j.*QRx1(n-i)),n,0,128);
          end

Walter Roberson 2017-2-10

在 MATLAB Online 中打开

You have not defined n in the above code, but you are using it as the symsum variable.

If you define n as numeric and starting at 1, then you would get an error from the IRX1(n-i) in the case when n and i are 1.

If you define n as sym, then you will get an error from one of the (n) or (n-i) indexing attempts. For one thing, you have IRx1(n) but you start n at 0. More importantly, though, is that you cannot index an array at a sym -- it is not a defined operation.

Do not use symsum() to sum a vector of definite values. Create the vector numerically and sum() it.

j = sqrt(-1);
n = 1 : 128;
IRx1 = sym('IRx1', [1 128]);  %are you sure you want to override the existing array??
QRx1 = sym('QRx1', [1 128]);  %are you sure you want to override the existing array??
for i=1:128
   this_entry = sum( (IRx1(n) + j.*QRx1(n)) .* (IRx1(n-i) - j.*QRx1(n-i)) );
   ACF1(i) = this_entry
 end

However, this is still going to fail because n-i is going to go non-positive and you cannot index arrays of symbols at non-positive numbers any more than you can index arrays of numbers at non-positive numbers.

Should you be circular shifting the vectors or something like that?

IRx1 = sym('IRx1', [1 128]);  %are you sure you want to override the existing array??
QRx1 = sym('QRx1', [1 128]);  %are you sure you want to override the existing array??
plain = complex(IRx1, QRx1);
for i = 1 : 128
  this_entry = sum( plain .* circshift(plain, [1 i]);
  ACF1(i) = this_entry;
end

... it would make more sense to me if you were doing this operation on the numeric arrays rather than symbolic IRx1 and QRx1

vinod kumar govindu 2017-2-10

编辑：vinod kumar govindu 2017-2-10

在 MATLAB Online 中打开

I am using MATLAB 7.6.0(R2008a)

and for

syms IRx1 QRx1

also it showing same error

Walter Roberson 2017-2-10

在 MATLAB Online 中打开

It sounds as if you do not have a symbolic toolbox installed, so I do not understand why your earlier code used syms. symsum cannot be used without the Symbolic Toolbox.

It did not make sense to me that you used syms there anyhow.

j = sqrt(-1);
n = 1 : 128;
for i=1:128
   this_entry = sum( (IRx1(n) + j.*QRx1(n)) .* (IRx1(n-i) - j.*QRx1(n-i)) );
   ACF1(i) = this_entry
 end

However, this will have the problem I described before. You are allowing i to exceed n, which is going to lead to negative subscripts.

I suspect your code should look more like

plain = complex(IRx1, QRx1);
for i = 1 : 128
  this_entry = sum( plain .* circshift(plain, [1 i]);
  ACF1(i) = this_entry;
end

请先登录，再进行评论。

How to find the location of approximately equal value in vector?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

采纳的回答

13 个评论
显示 11更早的评论隐藏 11更早的评论

更多回答（0 个）

另请参阅

类别

标签

Community Treasure Hunt

How to find the location of approximately equal value in vector?

0 个评论 显示 -2更早的评论隐藏 -2更早的评论

采纳的回答

13 个评论 显示 11更早的评论隐藏 11更早的评论

更多回答（0 个）

另请参阅

类别

标签

Community Treasure Hunt

WeChat

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

13 个评论
显示 11更早的评论隐藏 11更早的评论