Help with Coding problem

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christina 2018-7-5

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/408987-help-with-coding-problem

编辑： Abraham Boayue 2018-7-10

在 MATLAB Online 中打开

I am trying to code the following in matlab.

Following is my matlab code. But this doesn't give me the right result. Can somebody point out what am I doing wrong?

function [J] = funtc(x_t,c_mn,theta,M,N )
L = length(x_t );
l = 0:L-1;
m = 0:M-1; 
n = 0:N-1;
J = 0 ; 
for t = 1:L
    xs = 0 ;
    xp = 0 ;
    for j = 1: length(n)
        for k = 1: length(m)
            xs = xs + c_mn(k,j)*exp(-pi*(l(t)-n(j))^2/theta^2)*exp(1i*2*pi*m(k)*(l(t)- n(j))/M);
            xp = xp + c_mn(k,j)*exp(-pi*(l(t)-n(j))^2/theta^2)*exp(1i*2*pi*m(k)*(l(t)- n(j))/M)*(l(t)-n(j))^2/theta^3;
        end
    end
    J = J + ((x_t (t) -xs) * conj (xp));
end
J = real(-4*J);
end

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christina 2018-7-9

I use conj because c_mn can be complex valued. Also please ignore (1/sqrt(theta)) and a. I have removed it from my code above. Am I writing the update of J correctly?

Geoff Hayes 2018-7-9

But why just use conj on the one sum and not both?

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回答（1 个）

Abraham Boayue 2018-7-10

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/408987-help-with-coding-problem#answer_328154

编辑：Abraham Boayue 2018-7-10

在 MATLAB Online 中打开

Try this

function [J] = funtc(x_t,c,theta,M,N,L)
J = zeros(1,L); 
for t = 1:L
    xs = 0 ;
    xp = 0 ;
    for n = 1: N
        for m = 1: M
            xs = xs + c(n,m)*exp(-pi*((t-n)./theta)).^2*exp(1i*2*pi*m*(t- n)/M);
            xp = xp + c(n,m)*exp(-pi*((t-n)./theta).^2)*exp(1i*2*pi*m*(t- n)/M)*(t-n)^2./theta.^3;
        end
    end
    J = J + ((x_t (t) -xs).*conj (xp));
end
J = -4*real(J);
end

I tested this function using the mfile below.

L = 20;
N = 10;
M = 5;
c =round(10*rand(N,M)); 
theta0 = 0.96;
x0 = 4;
theta = 0:theta0/(L-1):theta0;
x_t = 0:x0/(L-1):x0; 
J =  funtc(x_t,c,theta,M,N ,L);
plot(theta,J);