Bug of matlab coder (2013a) for IFFT?

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laoya
laoya 2013-8-1
Dear all,
I am trying to use the matlab coder to generate C++ code for IFFT. However, results from matlab and C++ code have greate difference. Could anyone help me to take a look at this problem?
The matlab code to do IFFT is as follows:
z=ifft(y,[],1);
The data of y are as follows:
487924.35768878186
481026.24091831001
478940.94803639117
480926.64214804117
478909.92810891091
475591.66558611894
472961.12419697485
478082.98773687298
475963.06721005152
471624.91585664771
473035.01798060897
470885.04387918825
465204.72500935785
465559.98854017764
468284.20173525374
467779.54004903068
467358.62894582795
461658.53205369966
461058.87787927384
461185.53453021083
455868.37107306172
462911.95616388740
459834.12223788921
458194.44688116410
456595.68046306813
451450.72108931403
448915.17218837264
451224.11133871856
448603.78107835044
442943.27244258055
445878.56931863062
451008.71128154272
451212.54731590918
455779.62766682287
454335.89646260266
450941.74302688910
451440.15563114837
451448.07972477260
449064.57034377591
448331.01187180565
449871.73269351595
449496.69114039827
445229.11575907044
444080.89526586136
443461.78518676467
437449.62073759746
443516.19085396524
438574.10116169654
434403.16106846917
433751.71037962160
426817.29095258669
422633.17624841497
418137.67043422104
413457.43016094179
411045.60664053162
403724.29173170537
392643.02660994284
380096.57725000178
357723.60756075662
332111.19753204676
317106.73298398359
311326.13889686763
311656.30946454400
310753.51039134728
313637.04296473821
311065.22361899650
310994.64764692046
309178.16192473430
310382.78521443135
310153.53409929451
308257.54974676436
309423.90546237369
310570.45094392239
308946.62377444573
310466.56800921442
309782.13247536187
320356.73878161400
347570.20226357155
368694.03200706805
384869.13643517962
398566.44765287120
407737.20091712585
412582.04329780280
418070.05794431345
422272.98431790201
424134.63093139383
430451.22874984005
433175.44194491615
437468.43240701430
438150.54869395244
439138.45124420297
443049.79674182995
441973.82723235723
440130.96007651964
447706.58685186348
449457.42500166676
454555.58068421762
449613.45878018625
452690.29414154071
451600.11924471724
452466.32575548667
454145.23503918055
449159.24071435159
456451.88715437474
450130.32872447267
450516.57997100998
452118.30987127440
449933.06388969702
452284.90910795948
452236.75252272276
453562.39540488424
455035.18161905993
456251.33671980369
457868.23836029979
460014.57253253541
462557.04696245730
461771.33764667553
462317.90683617146
466403.38912295533
467626.46975267958
466153.36142087687
467724.10360542370
470285.06758713548
469912.31306916947
469812.71429890068
469016.11740732624
470695.70313803683
473460.18103648809
475000.22541118169
476990.88013428752
477611.31089565484
475078.08124162792
479902.43694122758
478081.34493697528
480799.95328534150
484503.82281941688
Thanks, Tang Laoya

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回答（3 个）

Sean de Wolski
Sean de Wolski 2013-8-1
编辑：Sean de Wolski 2013-8-1
I'm not surprised to see a small difference. Building a mex file from this:
function y = doIFFT(x)
y = ifft(x,2^nextpow2(numel(x)),1);
%I had to add the nextpow2 part to get it to build
end
Then looking at the differences:
norm(doIFFT(x)-doIFFT_mex(x))
ans =
4.695591604029106e-11
The difference is very small. In fact it's close to:
eps(487924.35768878186)
So this is just a small numerical round-off difference in the approach taken by the libraries MATLAB sits on and the generated c-code.
laoya
laoya 2013-8-1
编辑：laoya 2013-8-1
Hi Sean de Wolski,
Thanks for your quick reply. However, from here the difference is not so small. The results from matlab are: 1.0e+005 *
4.313512092938006
0.300430732843556 - 0.005783095388433i
-0.147813810099868 + 0.000951173782191i
0.133108569308995 - 0.003373860065190i
-0.061656447655613 + 0.003328454544711i
0.027192760859384 - 0.000603671006620i
-0.005797878506124 - 0.000492192018536i
-0.001061055121786 + 0.001998424724582i
0.021577859002924 - 0.002456894682518i
-0.021811429158957 + 0.003207842695919i
0.017735324252322 - 0.003028416146602i
-0.014305192477317 - 0.000474115939438i
0.013515213478997 - 0.002166798336642i
-0.004684409887853 + 0.003175414468610i
-0.000443185935397 + 0.000308035524811i
0.003853153787452 - 0.002023631130418i
-0.005850698801703 + 0.000216651950420i
0.012856303304599 - 0.001080645604734i
-0.005791634751852 + 0.002526085886894i
0.005578657992319 - 0.000926823744157i
-0.000112906707825 + 0.001805996486923i
0.001274493397202 + 0.000127337940853i
-0.001556944764524 - 0.000427023062860i
-0.002102718086437 - 0.000349736278996i
0.002944493706193 - 0.003170105190536i
-0.001861635715701 - 0.000525536225213i
0.002975662968139 - 0.000719539330124i
-0.002191858687055 + 0.000974062580574i
0.000491769705110 - 0.001428164102981i
-0.000607238680120 - 0.000256915753116i
0.002503276464045 + 0.001201049865073i
0.000502580943466 - 0.000828435382671i
-0.001255667660083 + 0.000254113854892i
0.001911608261996 - 0.002132432317272i
-0.000122452068500 - 0.001590327883673i
0.000678876401114 - 0.002190333520453i
0.000850110098716 + 0.001294448469562i
0.002221809217307 - 0.000687101621501i
0.001690063348324 - 0.000139630162640i
0.001283562042216 + 0.000855341907948i
0.002625543849526 - 0.001037104423102i
0.000443377947227 + 0.002073096558817i
-0.000133656504791 - 0.000054353863241i
-0.001507985869583 - 0.001123830171823i
0.001803796928052 - 0.000319702526871i
0.000802884469623 + 0.001769241259875i
0.000017848403353 + 0.000495263516297i
-0.000878046846166 - 0.002090322061183i
-0.001684884158707 + 0.000640259092086i
0.000349058948051 - 0.002674201272202i
0.001317964739399 - 0.000682460501570i
0.000136079066329 - 0.000196295344922i
-0.000751139021633 - 0.000771625053355i
0.001165570869108 + 0.001735364213629i
-0.000174024655019 + 0.001713751491137i
-0.000142209151696 - 0.001924788489301i
-0.001616076044371 - 0.000170224894442i
0.000779708646816 + 0.001697818033402i
0.002037664934465 - 0.000305846247259i
0.000752313211467 - 0.000118969236097i
-0.001010826774948 + 0.001686222917862i
-0.000086432763696 + 0.000856642401964i
0.001333583110647 + 0.000499768614078i
-0.000941810898597 - 0.000492021314954i
0.000162814303691 + 0.000686033402377i
0.001251368703072 + 0.000230732674254i
0.000737206223204 + 0.000479604300745i
-0.000537515690459 + 0.000473585154103i
0.000927698765764
-0.000537515690459 - 0.000473585154103i
0.000737206223204 - 0.000479604300745i
0.001251368703072 - 0.000230732674254i
0.000162814303691 - 0.000686033402377i
-0.000941810898597 + 0.000492021314954i
0.001333583110647 - 0.000499768614078i
-0.000086432763696 - 0.000856642401964i
-0.001010826774948 - 0.001686222917862i
0.000752313211467 + 0.000118969236097i
0.002037664934465 + 0.000305846247259i
0.000779708646816 - 0.001697818033402i
-0.001616076044371 + 0.000170224894442i
-0.000142209151696 + 0.001924788489301i
-0.000174024655019 - 0.001713751491137i
0.001165570869108 - 0.001735364213629i
-0.000751139021633 + 0.000771625053355i
0.000136079066329 + 0.000196295344922i
0.001317964739399 + 0.000682460501571i
0.000349058948051 + 0.002674201272202i
-0.001684884158707 - 0.000640259092086i
-0.000878046846166 + 0.002090322061183i
0.000017848403353 - 0.000495263516297i
0.000802884469623 - 0.001769241259875i
0.001803796928052 + 0.000319702526871i
-0.001507985869583 + 0.001123830171823i
-0.000133656504791 + 0.000054353863241i
0.000443377947227 - 0.002073096558817i
0.002625543849526 + 0.001037104423102i
0.001283562042216 - 0.000855341907948i
0.001690063348324 + 0.000139630162640i
0.002221809217307 + 0.000687101621501i
0.000850110098716 - 0.001294448469563i
0.000678876401114 + 0.002190333520453i
-0.000122452068500 + 0.001590327883673i
0.001911608261996 + 0.002132432317272i
-0.001255667660083 - 0.000254113854892i
0.000502580943466 + 0.000828435382671i
0.002503276464045 - 0.001201049865073i
-0.000607238680120 + 0.000256915753116i
0.000491769705110 + 0.001428164102981i
-0.002191858687055 - 0.000974062580574i
0.002975662968139 + 0.000719539330124i
-0.001861635715701 + 0.000525536225213i
0.002944493706193 + 0.003170105190536i
-0.002102718086437 + 0.000349736278996i
-0.001556944764524 + 0.000427023062860i
0.001274493397202 - 0.000127337940853i
-0.000112906707825 - 0.001805996486923i
0.005578657992319 + 0.000926823744157i
-0.005791634751852 - 0.002526085886894i
0.012856303304599 + 0.001080645604734i
-0.005850698801703 - 0.000216651950420i
0.003853153787452 + 0.002023631130418i
-0.000443185935397 - 0.000308035524811i
-0.004684409887853 - 0.003175414468610i
0.013515213478997 + 0.002166798336642i
-0.014305192477317 + 0.000474115939438i
0.017735324252322 + 0.003028416146602i
-0.021811429158957 - 0.003207842695919i
0.021577859002924 + 0.002456894682518i
-0.001061055121786 - 0.001998424724582i
-0.005797878506124 + 0.000492192018536i
0.027192760859384 + 0.000603671006620i
-0.061656447655613 - 0.003328454544711i
0.133108569308995 + 0.003373860065190i
-0.147813810099868 - 0.000951173782191i
0.300430732843556 + 0.005783095388433i
But results from C++ code are as follows:
72422.083779590306 -21175.927029026894
11125.992351540337 3106.1219836735977
6843.8805862924828 3554.4005362181247
4356.1650364638035 2570.7688328224426
3420.3547292047629 0.31787260351634089
4700.1741689654591 -2577.2663742471132
7910.0731580255633 -3855.9217257203227
13419.434500006109 -4115.2819077652211
-13282.696522193037 -30704.471141475420
7971.4850412689193 3265.5656871257138
5862.2579664486675 4181.4237102004063
3696.9860231590023 2941.4488545757381
3051.9471877097153 129.42359763279092
4852.0985869896149 -2863.1910672093150
9114.7261030580539 -5404.2257888381619
48675.808343791687 -29709.095883131220
-34398.075003605700 -18366.992612829283
5138.7854450924133 4996.7355815242800
4654.2058745860568 4864.4564801580163
1543.8705522082814 4071.7857881112859
1819.7875797722779 457.90605746160725
2830.8298912636742 -2275.1392367139283
9716.4329594613992 -7783.0865968464159
-3630.7897718976387 9142.7833067804131
-8845.6457668685016 414.34287820314398
4992.1599224602105 4868.9723525938753
3229.5822994476157 4878.3164657138086
736.67044680706999 3430.1969587796079
957.35710922778412 -1031.5653556290436
2480.5289862458612 -5208.5851937693360
25700.781958828022 -39844.385866482604
-394.49267492773350 7591.7737507502407
-20665.267900238770 27776.650484342088
-1473.5210380044171 4785.8222036708621
60.051900129337277 7119.4630475685044
-830.62218704141992 3490.4524725087017
-1074.6118697358522 -875.00645669774576
2877.6149243907121 -9498.2795773337984
-9229.4478008981059 18304.491631238121
308.96239530547393 4249.9275609692568
-2404.7107375548189 8985.3059745066676
2132.7840149464282 4447.5810777565584
-477.38110141003563 4978.7152523136738
-2549.9004910493386 2030.8234215058337
-3073.6612221284904 -4054.7995961807842
5432.9358533986097 -38643.332288489612
-3605.4539005091733 9775.7604208193752
45.552641515049103 4113.9140568298253
221.05280647733633 12207.662006532393
-278.76886434015228 7710.8290184780490
-1890.2508641515733 3916.7204912494567
-4536.8419186779274 2104.3932757967714
-5059.1810510076248 -8576.6255176689756
-6110.5398786129972 29323.824846673553
-2794.5666980626256 4779.6064599904876
-198.13055532286543 1728.5801399849456
1797.5246407960512 3609.7437062598865
-576.50490459068919 3309.6370867571586
-3325.1497702358815 1971.7321719294284
-6523.0645758753290 -1698.9721656553158
-12240.582997565247 -30058.889007986600
-2717.1305815325768 11518.450610493081
-1454.2548795338439 4192.0167255739652
52.786090168379495 1026.7177630023957
-10338.642087783273 13642.323636409885
-6812.9003180914069 2866.9799795768654
-3792.8505170487479 -230.78805726075026
-7213.3223499798705 -7679.6190964047646
321.28615576961795 36259.999009415274
-4383.7395961326183 3415.7340629150949
-2309.0277783778693 -1088.5516338423911
-180.79148605519302 -1836.5173221714188
743.63999390828008 -6101.2152527950202
-1134.2989609607107 -524.23819381373767
-4792.5955569409125 -2348.0148101847226
-14766.177531123119 -21182.107722402230
-439.08920376328257 10344.607622734815
-2542.4461870583073 599.14559236859304
-845.19793586519643 -2599.3865384547471
1187.5292526634566 -2785.6446093624072
-9038.0486912758315 -7065.9521600213020
80.625318829726467 10.714344970158622
-5653.8415272376815 -4732.4052208226767
21190.907021163606 37007.587554493541
-852.94447933068420 3637.7765490408310
-2098.0122985887024 -2686.0869132157095
261.25956450206797 -4322.5060757986057
1970.2539612731198 -4518.7374882269842
-7274.3941270798468 -4518.5287317769698
-330.11620341411918 -2225.0447706025757
-11852.288982194095 -10043.221245743609
6679.5226265230413 7775.3855646021684
1377.9236897985454 1025.0031917079912
113.67914951110266 -3664.2480443867912
3090.0901443598441 -4740.7616094401865
4285.8937306032358 -4849.8787958145267
-24356.495771448343 14480.960943266133
-5295.8195730284415 -3506.5828383575276
40818.185859963669 30465.471866954791
3565.6822875299658 3109.8019153641180
997.99930535255316 -1037.8513161753970
1596.4431752630942 -4058.2212596692852
2371.8530430438618 -6235.0706981591920
5157.0953715735923 -5258.0134317301263
-5483.7061459089282 6393.6879372332833
-2472.6887179699484 -4024.0136908333516
11191.498476511286 4243.0178602305305
4326.6288886882658 1068.9429182750932
2523.3147519425652 -1914.9842759916771
4750.3542365514413 -4293.9197562996178
4884.6046593881738 -6045.4671383659079
7723.2247447638074 -4995.1376654136848
-8572.1840474269666 38548.652251609477
57941.834946725779 12129.156253256031
8352.6956653903162 2187.0454560172848
3106.6583415751998 386.09826727500115
3429.7058523298415 -1988.1225111991816
1628.0516246254488 -4714.1787317279168
5902.3957729349340 -5738.5628963074414
8049.8073106827114 -4652.4255896710165
9145.3967079252434 32125.876528317396
12010.057611526385 766.20021100067629
8174.8653008944102 1558.3663819684973
4622.4202209866007 570.29637943909381
5678.5596863576793 -2317.1898630674232
3994.7403360780213 -4371.9898884749864
8688.5972400898154 -5958.6490558767273
10928.004975388818 -5130.2471041175613
2965.8936925455027 8488.5318855891073
1091.4535707318753 -1704.1399129821730
-3792.8505170487479 -230.78805726075026
-7213.3223499798705 -7679.6190964047646
0.00000000000000000 0.00000000000000000
0.00000000000000000 0.00000000000000000
0.00000000000000000 0.00000000000000000
0.00000000000000000 0.00000000000000000
C++ codes generated by matlab coder are:
/// ifft.c
/* * ifft.c * * Code generation for function 'ifft' * * C source code generated on: Thu Aug 01 16:42:35 2013 * */
/* Include files */
#include "rt_nonfinite.h"
#include "Dissociation.h"
#include "ifft.h"
#include "Dissociation_emxutil.h"
#include "Dissociation_rtwutil.h"
/* Function Definitions */
/* * */ void b_ifft(const emxArray_creal_T *x, emxArray_creal_T *y)
{
uint32_T sz[2];
int32_T ju;
int32_T minval;
emxArray_real_T *costab1q;
int32_T nd2;
int32_T ixDelta;
int32_T nRowsD2;
int32_T nRowsD4;
int32_T lastChan;
real_T e;
int32_T k;
emxArray_real_T *costab;
emxArray_real_T *sintab;
int32_T ix;
int32_T chanStart;
int32_T i;
boolean_T tst;
real_T temp_re;
real_T temp_im;
int32_T iDelta;
int32_T iDelta2;
int32_T iheight;
int32_T ihi;
real_T twid_im;
for (ju = 0; ju < 2; ju++) {
sz[ju] = (uint32_T)x->size[ju];
}
ju = y->size[0] * y->size[1];
y->size[0] = x->size[0];
y->size[1] = (int32_T)sz[1];
emxEnsureCapacity((emxArray__common *)y, ju, (int32_T)sizeof(creal_T));
if ((x->size[0] == 0) || (x->size[1] == 0)) {
} else {
minval = x->size[0];
b_emxInit_real_T(&costab1q, 2);
nd2 = (x->size[0] - minval) + 1;
if (1 >= nd2) {
ixDelta = 1;
} else {
ixDelta = nd2;
}
ju = x->size[0];
nRowsD2 = ju / 2;
nRowsD4 = nRowsD2 / 2;
lastChan = x->size[0] * (div_s32(x->size[0] * x->size[1], x->size[0]) - 1);
e = 6.2831853071795862 / (real_T)x->size[0];
ju = costab1q->size[0] * costab1q->size[1];
costab1q->size[0] = 1;
costab1q->size[1] = nRowsD4 + 1;
emxEnsureCapacity((emxArray__common *)costab1q, ju, (int32_T)sizeof(real_T));
costab1q->data[0] = 1.0;
nd2 = nRowsD4 / 2;
for (k = 1; k <= nd2; k++) {
costab1q->data[k] = cos(e * (real_T)k);
}
for (k = nd2 + 1; k < nRowsD4; k++) {
costab1q->data[k] = sin(e * (real_T)(nRowsD4 - k));
}
b_emxInit_real_T(&costab, 2);
b_emxInit_real_T(&sintab, 2);
costab1q->data[nRowsD4] = 0.0;
nd2 = (costab1q->size[1] - 1) << 1;
ju = costab->size[0] * costab->size[1];
costab->size[0] = 1;
costab->size[1] = nd2 + 1;
emxEnsureCapacity((emxArray__common *)costab, ju, (int32_T)sizeof(real_T));
ju = sintab->size[0] * sintab->size[1];
sintab->size[0] = 1;
sintab->size[1] = nd2 + 1;
emxEnsureCapacity((emxArray__common *)sintab, ju, (int32_T)sizeof(real_T));
costab->data[0] = 1.0;
sintab->data[0] = 0.0;
for (k = 1; k < costab1q->size[1]; k++) {
costab->data[k] = costab1q->data[k];
sintab->data[k] = costab1q->data[(costab1q->size[1] - k) - 1];
}
for (k = costab1q->size[1]; k <= nd2; k++) {
costab->data[k] = -costab1q->data[nd2 - k];
sintab->data[k] = costab1q->data[(k - costab1q->size[1]) + 1];
}
emxFree_real_T(&costab1q);
ix = 0;
for (chanStart = 0; chanStart <= lastChan; chanStart += x->size[0]) {
ju = 0;
nd2 = chanStart;
for (i = 1; i < minval; i++) {
y->data[nd2] = x->data[ix];
nd2 = x->size[0];
tst = TRUE;
while (tst) {
nd2 >>= 1;
ju ^= nd2;
tst = ((ju & nd2) == 0);
}
nd2 = chanStart + ju;
ix++;
}
y->data[nd2] = x->data[ix];
ix += ixDelta;
ju = (chanStart + x->size[0]) - 2;
if (x->size[0] > 1) {
for (i = chanStart; i <= ju; i += 2) {
temp_re = y->data[i + 1].re;
temp_im = y->data[i + 1].im;
y->data[i + 1].re = y->data[i].re - y->data[i + 1].re;
y->data[i + 1].im = y->data[i].im - y->data[i + 1].im;
y->data[i].re += temp_re;
y->data[i].im += temp_im;
}
}
iDelta = 2;
iDelta2 = 4;
k = nRowsD4;
iheight = 1 + ((nRowsD4 - 1) << 2);
while (k > 0) {
i = chanStart;
ihi = chanStart + iheight;
while (i < ihi) {
nd2 = i + iDelta;
temp_re = y->data[nd2].re;
temp_im = y->data[nd2].im;
y->data[i + iDelta].re = y->data[i].re - y->data[nd2].re;
y->data[i + iDelta].im = y->data[i].im - y->data[nd2].im;
y->data[i].re += temp_re;
y->data[i].im += temp_im;
i += iDelta2;
}
nd2 = chanStart + 1;
for (ju = k; ju < nRowsD2; ju += k) {
e = costab->data[ju];
twid_im = sintab->data[ju];
i = nd2;
ihi = nd2 + iheight;
while (i < ihi) {
temp_re = e * y->data[i + iDelta].re - twid_im * y->data[i + iDelta]
.im;
temp_im = e * y->data[i + iDelta].im + twid_im * y->data[i + iDelta]
.re;
y->data[i + iDelta].re = y->data[i].re - temp_re;
y->data[i + iDelta].im = y->data[i].im - temp_im;
y->data[i].re += temp_re;
y->data[i].im += temp_im;
i += iDelta2;
}
nd2++;
}
k /= 2;
iDelta = iDelta2;
iDelta2 <<= 1;
iheight -= iDelta;
}
}
emxFree_real_T(&sintab);
emxFree_real_T(&costab);
if (y->size[0] > 1) {
e = 1.0 / (real_T)y->size[0];
ju = y->size[0] * y->size[1];
emxEnsureCapacity((emxArray__common *)y, ju, (int32_T)sizeof(creal_T));
nd2 = y->size[0];
ju = y->size[1];
nd2 *= ju;
for (ju = 0; ju < nd2; ju++) {
y->data[ju].re *= e;
y->data[ju].im *= e;
}
}
}
}
/* * */
void ifft(const emxArray_real_T *x, emxArray_creal_T *y)
{
int32_T ju;
int32_T minval;
emxArray_real_T *costab1q;
int32_T nd2;
int32_T ixDelta;
int32_T nRowsD2;
int32_T nRowsD4;
int32_T lastChan;
real_T e;
int32_T k;
emxArray_real_T *costab;
emxArray_real_T *sintab;
int32_T ix;
int32_T chanStart;
int32_T i;
boolean_T tst;
real_T temp_re;
real_T temp_im;
int32_T iDelta;
int32_T iDelta2;
int32_T iheight;
int32_T ihi;
real_T twid_im;
ju = y->size[0];
y->size[0] = x->size[0];
emxEnsureCapacity((emxArray__common *)y, ju, (int32_T)sizeof(creal_T));
if (x->size[0] == 0) {
} else {
minval = x->size[0];
b_emxInit_real_T(&costab1q, 2);
nd2 = (x->size[0] - minval) + 1;
if (1 >= nd2) {
ixDelta = 1;
} else {
ixDelta = nd2;
}
ju = x->size[0];
nRowsD2 = ju / 2;
nRowsD4 = nRowsD2 / 2;
lastChan = x->size[0] * (div_s32(x->size[0], x->size[0]) - 1);
e = 6.2831853071795862 / (real_T)x->size[0];
ju = costab1q->size[0] * costab1q->size[1];
costab1q->size[0] = 1;
costab1q->size[1] = nRowsD4 + 1;
emxEnsureCapacity((emxArray__common *)costab1q, ju, (int32_T)sizeof(real_T));
costab1q->data[0] = 1.0;
nd2 = nRowsD4 / 2;
for (k = 1; k <= nd2; k++) {
costab1q->data[k] = cos(e * (real_T)k);
}
for (k = nd2 + 1; k < nRowsD4; k++) {
costab1q->data[k] = sin(e * (real_T)(nRowsD4 - k));
}
b_emxInit_real_T(&costab, 2);
b_emxInit_real_T(&sintab, 2);
costab1q->data[nRowsD4] = 0.0;
nd2 = (costab1q->size[1] - 1) << 1;
ju = costab->size[0] * costab->size[1];
costab->size[0] = 1;
costab->size[1] = nd2 + 1;
emxEnsureCapacity((emxArray__common *)costab, ju, (int32_T)sizeof(real_T));
ju = sintab->size[0] * sintab->size[1];
sintab->size[0] = 1;
sintab->size[1] = nd2 + 1;
emxEnsureCapacity((emxArray__common *)sintab, ju, (int32_T)sizeof(real_T));
costab->data[0] = 1.0;
sintab->data[0] = 0.0;
for (k = 1; k < costab1q->size[1]; k++) {
costab->data[k] = costab1q->data[k];
sintab->data[k] = costab1q->data[(costab1q->size[1] - k) - 1];
}
for (k = costab1q->size[1]; k <= nd2; k++) {
costab->data[k] = -costab1q->data[nd2 - k];
sintab->data[k] = costab1q->data[(k - costab1q->size[1]) + 1];
}
emxFree_real_T(&costab1q);
ix = 0;
for (chanStart = 0; chanStart <= lastChan; chanStart += x->size[0]) {
ju = 0;
nd2 = chanStart;
for (i = 1; i < minval; i++) {
y->data[nd2].re = x->data[ix];
y->data[nd2].im = 0.0;
nd2 = x->size[0];
tst = TRUE;
while (tst) {
nd2 >>= 1;
ju ^= nd2;
tst = ((ju & nd2) == 0);
}
nd2 = chanStart + ju;
ix++;
}
y->data[nd2].re = x->data[ix];
y->data[nd2].im = 0.0;
ix += ixDelta;
nd2 = (chanStart + x->size[0]) - 2;
if (x->size[0] > 1) {
for (i = chanStart; i <= nd2; i += 2) {
temp_re = y->data[i + 1].re;
temp_im = y->data[i + 1].im;
y->data[i + 1].re = y->data[i].re - y->data[i + 1].re;
y->data[i + 1].im = y->data[i].im - y->data[i + 1].im;
y->data[i].re += temp_re;
y->data[i].im += temp_im;
}
}
iDelta = 2;
iDelta2 = 4;
k = nRowsD4;
iheight = 1 + ((nRowsD4 - 1) << 2);
while (k > 0) {
i = chanStart;
ihi = chanStart + iheight;
while (i < ihi) {
nd2 = i + iDelta;
temp_re = y->data[nd2].re;
temp_im = y->data[nd2].im;
y->data[i + iDelta].re = y->data[i].re - y->data[nd2].re;
y->data[i + iDelta].im = y->data[i].im - y->data[nd2].im;
y->data[i].re += temp_re;
y->data[i].im += temp_im;
i += iDelta2;
}
nd2 = chanStart + 1;
for (ju = k; ju < nRowsD2; ju += k) {
e = costab->data[ju];
twid_im = sintab->data[ju];
i = nd2;
ihi = nd2 + iheight;
while (i < ihi) {
temp_re = e * y->data[i + iDelta].re - twid_im * y->data[i + iDelta]
.im;
temp_im = e * y->data[i + iDelta].im + twid_im * y->data[i + iDelta]
.re;
y->data[i + iDelta].re = y->data[i].re - temp_re;
y->data[i + iDelta].im = y->data[i].im - temp_im;
y->data[i].re += temp_re;
y->data[i].im += temp_im;
i += iDelta2;
}
nd2++;
}
k /= 2;
iDelta = iDelta2;
iDelta2 <<= 1;
iheight -= iDelta;
}
}
emxFree_real_T(&sintab);
emxFree_real_T(&costab);
if (y->size[0] > 1) {
e = 1.0 / (real_T)y->size[0];
ju = y->size[0];
emxEnsureCapacity((emxArray__common *)y, ju, (int32_T)sizeof(creal_T));
nd2 = y->size[0];
for (ju = 0; ju < nd2; ju++) {
y->data[ju].re *= e;
y->data[ju].im *= e;
}
}
}
}
/* End of code generation (ifft.c) */
Thanks, Tang Laoya
  4 个评论
显示 2更早的评论
Sean de Wolski
Sean de Wolski 2013-8-1
If you download the same file from here:
http://www.mathworks.com/matlabcentral/fileexchange/26385-resize-any-arrays-and-images
Then you can make changes to it since it's covered under BSD.
laoya
laoya 2013-8-1
编辑：laoya 2013-8-1
Dear Sean de Wolski,
Thanks again for your kindly reply. Could yoy please give me more suggestion about how to resize the array to get almost the same result as the matlab code?
y = ifft(x,[],1);
What I mean that I can't modify the code is that that's a classical function and I have got reasonable results by matlab code using that function. However, if I modify the code to calculate the IFFT, the final results are totally different from what I got currently.
In fact, I have found another FFT source code by by Jens Joergen Nielsen (<http://www.jjj.de/fft/mixfft03.zip>) from here:
http://www.jjj.de/fft/fftpage.html
and write my own code as follows:
function y=ifft2(x)
x=conj(x);
% y=fft(x,[],1);
y=myfft(x,length(x)); % from mixfft03
y=conj(y)/length(x);
The results are the same as that from matlab. So it shows that it is a bug of matlab coder.
Thanks,
Tang Laoya

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laoya
laoya 2013-8-7
Dear all,
I found another bug of matlab (2013a) coder. When 'a' is a vector with size 1*N, the generated C code will crash for the following matlab code:
b=diff(a,2);
however, if I change the code to the following, the C code works:
b=diff(a',2);
Could anyone help me to take a look at it?
Thanks, Tang Laoya

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