How to find the x and y coordinates of the maximum value in curve without defferntiaition

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yousef Yousef 2015-6-4

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评论： Alfonso Nieto-Castanon 2015-6-5

采纳的回答： Image Analyst

Hi I have a curve,I want to find x and y coordinate of the maximum value Thanks

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James Tursa 2015-6-4

In what form do you have the curve? A one line definition? A function file? Or what?

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Image Analyst 2015-6-4

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在 MATLAB Online 中打开

If x and y are in arrays, how about

[maxY, indexOfMaxY] = max(y);
xAtMaxY = x(indexOfMaxY);

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yousef Yousef 2015-6-5

编辑：Image Analyst 2015-6-5

在 MATLAB Online 中打开

clc
clear all
format long
N=200;
doa=[20 60]/180*pi;
w=[pi/4 pi/4]';
M=10;
P=length(w);
lambda=150;
d=lambda/2;
snr=20;
D=zeros(P,M);
for k=1:P
  D(k,:)=exp(-j*2*pi*d*sin(doa(k))/lambda*[0:M-1]);
end
D=D';
xx=2*exp(j*(w*[1:N]));
x=D*xx;
x=x+awgn(x,snr);
R=x*x';
[N,V]=eig(R);
NN=N(:,1:M-P);
theta=-90:0.5:90;
for ii=1:length(theta)
  SS=zeros(1,length(M));
  for jj=0:M-1
    SS(1+jj)=exp(-j*2*jj*pi*d*sin(theta(ii)/180*pi)/lambda);
  end
  
  clc
  clear all
  format long
  N=200;
  doa=[20 60]/180*pi;
  w=[pi/4 pi/4]';
  M=10;
  P=length(w);
  lambda=150;
  d=lambda/2;
  snr=20;
  D=zeros(P,M);
  for k=1:P
    D(k,:)=exp(-j*2*pi*d*sin(doa(k))/lambda*[0:M-1]);
  end
  D=D';
  xx=2*exp(j*(w*[1:N]));
  x=D*xx;
  x=x+awgn(x,snr);
  R=x*x';
  [N,V]=eig(R);
  NN=N(:,1:M-P);
  theta=-90:0.5:90;
  for ii=1:length(theta)
    SS=zeros(1,length(M));
    for jj=0:M-1
      SS(1+jj)=exp(-j*2*jj*pi*d*sin(theta(ii)/180*pi)/lambda);
    end
    PP=SS*NN*NN'*SS';
    Pmusic(ii)=abs(1/ PP);
  end
  Pmusic=10*log10(Pmusic/max(Pmusic));
  plot(theta,Pmusic,'-k')
  xlabel('angle \theta/degree')
  ylabel('spectrum function P(\theta) /dB')
  title('DOA estimation based on MUSIC algorithm')
  grid on
  PP=SS*NN*NN'*SS';
  Pmusic(ii)=abs(1/ PP);
end
Pmusic=10*log10(Pmusic/max(Pmusic));
plot(theta,Pmusic,'-k')
xlabel('angle \theta/degree')
ylabel('spectrum function P(\theta) /dB')
title('DOA estimation based on MUSIC algorithm')
grid on

yousef Yousef 2015-6-5

Music_2.m

Hi,Thanks for you feeling,you will find every thing in the attached file. Thanks

Image Analyst 2015-6-5

I hope someone with the Communications toolbox can help you. I don't have that so I can't run your code, specifically the awgn() function. I did format it for you though and added the Communications Toolbox to the product list above.

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yousef Yousef 2015-6-5

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https://ww2.mathworks.cn/matlabcentral/answers/222517-how-to-find-the-x-and-y-coordinates-of-the-maximum-value-in-curve-without-defferntiaition#answer_181694

编辑：yousef Yousef 2015-6-5

z=abs(P);
zz=round(z);
ymax=max(zz);
xmax=THETA(find (zz==ymax));
However ,if somebody has better solution,I kindly ask hem or her to provide me with.Thanks

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yousef Yousef 2015-6-5

Thanks I think it is working great.But I still need to run it so many times to be sure.I will assure you if there is a problem in the results with this way of solving or not. Thanks a lot

Alfonso Nieto-Castanon 2015-6-5