I am plotting the derivative of a curve. Getting the y value for maximum peak height of the biggest peak. But when I try to get the x value corresponding to that y value its not giving me any value. Following is the code. Any help would be appreciate

Question

Anuradha Bhattacharya on 4 Oct 2016

0
Link

Direct link to this question

https://se.mathworks.com/matlabcentral/answers/305631-i-am-plotting-the-derivative-of-a-curve-getting-the-y-value-for-maximum-peak-height-of-the-biggest

Commented: Anuradha Bhattacharya on 4 Oct 2016

   a = load('ra1.dat');
    x = a(:,1);
    y = a(:,2);
    y_mov_average = filter(ones(1,50)/50,1,y);
    plot(x,y);
    hold on
    dy = diff(y)./diff(x);
    dy_mov_average = filter(ones(1,10)/10,1,dy);
    plot(x(2:end),dy_mov_average);
    PEAKSID = findpeaks(dy_mov_average);
    ID = class(PEAKSID);
    PEAKIDCAL = double(max(PEAKSID));
    VALUE = find(y==PEAKIDCAL);
    xaty = x(VALUE);
A portion of the ra1.dat is pasted below. Its a force distance plot by atomic force microscope.
-1.602783
8824  -1.604004
7649  -1.603394
6473  -1.602783
5298  -1.602478
4122  -1.602173
2946  -1.601563
1771  -1.601868
0595  -1.602478
942  -1.601868
8244  -1.602478
7068  -1.602478
5893  -1.602173
4717  -1.602478
3542  -1.603088
2366  -1.603699
1191  -1.601868
0015  -1.602783
8839  -1.603088
7664  -1.603394
6488  -1.604004
5313  -1.603088
4137  -1.604309
2961  -1.604004
1786  -1.603394
061  -1.604614
9435  -1.604004
8259  -1.604919
7084  -1.604004
5908  -1.603394
4732  -1.604309
3557  -1.604614
2381  -1.604614
1205  -1.604004
003  -1.60553
8854  -1.604309
7679  -1.604309
6503  -1.604614
5328  -1.604004
4152  -1.604004
2977  -1.604614
1801  -1.604919
0625  -1.604614
9449  -1.60553
8274  -1.604309
7098  -1.605225
5923  -1.606445
4747  -1.60675
3572  -1.60614
2396  -1.60614
1221  -1.60553
0045  -1.604614
887  -1.603394
7694  -1.603699
6518  -1.604919
5342  -1.60553
4167  -1.60553
2991  -1.604614
1816  -1.604919
064  -1.605835
9465  -1.60553
8289  -1.60553
7114  -1.60553
5938  -1.606445
4763  -1.605835
3587  -1.60614
2411  -1.604919
1235  -1.605835
006  -1.60553
8884  -1.60553
7709  -1.60675
6533  -1.607056
5358  -1.607666
4182  -1.607666
3007  -1.607056
1831  -1.607666
0656  -1.606445
948  -1.607971
8304  -1.607666
7128  -1.607056
5953  -1.607361
4777  -1.608276
3602  -1.607056
2426  -1.60614
1251  -1.608582
0075  -1.608887
89  -1.609802
7724  -1.609192
6548  -1.608887
5373  -1.608276
4197  -1.608582
3021  -1.609802
1846  -1.608276
067  -1.608276
9495  -1.609802
8319  -1.609497
7144  -1.609497
5968  -1.609802
4792  -1.610107
3617  -1.608276
2441  -1.608276
1266  -1.607666
009  -1.608887
8914  -1.608276
7739  -1.608582
6563  -1.608887
5388  -1.608582
4212  -1.609802
3036  -1.609192
1861  -1.610107
0685  -1.609802
951  -1.610107
8334  -1.609192
7159  -1.609192
5983  -1.610107
4807  -1.609802
3632  -1.609802
2456  -1.611023
1281  -1.609802
0105  -1.610718
8929  -1.610107
7754  -1.610413
6578  -1.609802
5403  -1.611633
4227  -1.611328
3052  -1.610718
1876  -1.610718
07  -1.611023
9525  -1.611328
8349  -1.611328
7173  -1.613159
5998  -1.612244
4822  -1.612244
3647  -1.612244
2471  -1.611633
1296  -1.611023
012  -1.611938
8944  -1.612854
7769  -1.613464
6593  -1.613159
5417  -1.612854
4242  -1.61377
3066  -1.61377
1891  -1.61377
0715  -1.613464
954  -1.613464
8364  -1.611328
7189  -1.611938
6013  -1.611938
4837  -1.611633
3661  -1.612549
2486  -1.61438
131  -1.612854
0135  -1.612549
8959  -1.613159
7784  -1.614075
6608  -1.613464
5433  -1.612854
4257  -1.613464
3082  -1.613464
1906  -1.612549
073  -1.612244
9554  -1.613464
8379  -1.613159
7203  -1.613464
6028  -1.61377
4852  -1.614075
3677  -1.61377
2501  -1.614075
1326  -1.61438
015  -1.615295
8975  -1.615906
7799  -1.615906
6623  -1.61499
5447  -1.616211
4272  -1.61499
3096  -1.61499
1921  -1.616211
0745  -1.615295
957  -1.615601
8394  -1.616211
7219  -1.615601
6043  -1.61499
4868  -1.615601
3692  -1.617432
2516  -1.615906
134  -1.615601
0165  -1.617126
8989  -1.617737
7814  -1.617126
6638  -1.616821
5463  -1.617432
4287  -1.617432
3112  -1.617737
1936  -1.618347
076  -1.618347
9585  -1.618347
8409  -1.618958
7233  -1.618347
6058  -1.618958
4882  -1.618042
3707  -1.618652
2531  -1.618652
1356  -1.618652
018  -1.618958
9005  -1.618958
7829  -1.618958
6653  -1.619873
5478  -1.620483

0 Comments
Show -2 older commentsHide -2 older comments

Sign in to comment.

Sign in to answer this question.

Answer 1

KSSV on 4 Oct 2016

1
Link

Direct link to this answer

https://se.mathworks.com/matlabcentral/answers/305631-i-am-plotting-the-derivative-of-a-curve-getting-the-y-value-for-maximum-peak-height-of-the-biggest#answer_237227

Edited: KSSV on 4 Oct 2016

Open in MATLAB Online

You can get the position/index of the maximum element from array using max itself. You need not to find the index later.

a = load('ra1.dat');
x = a(:,1);
y = a(:,2);
y_mov_average = filter(ones(1,50)/50,1,y);
plot(x,y);
hold on
dy = diff(y)./diff(x);
dy_mov_average = filter(ones(1,10)/10,1,dy);
plot(x(2:end),dy_mov_average);
PEAKSID = findpeaks(dy_mov_average);
ID = class(PEAKSID);
[PEAKIDCAL,VALUE] = (max(PEAKSID));  % get max and it's index 
% VALUE = find(y==PEAKIDCAL);
xaty = x(VALUE);

4 Comments
Show 2 older commentsHide 2 older comments

KSSV on 4 Oct 2016

max gives the maximum..the second cannot be greater. Your first code was not working because, you were equating floating numbers, which you should not.

Anuradha Bhattacharya on 4 Oct 2016