Error using dbscan. Expected X to be nonempty

I have written a code that converts phase differences to path differenes. There seems to be an error while using dbscan. How can I fix this error? Thanks for the help

This is my code :

lambda = 34.64; % in cm, considering 866MhZ frequency

pathData_1 = zeros(1,6);
for i=1:5
    theta=PhData_1(i+1)-PhData_1(i);
    thetaRad=pi*theta/180;
    pathData_1(i)=(thetaRad)*lambda/(4*pi);
end

a=pathData_1/2;
c=ones(1,6).*4; % fixed 8cm distance between two antenna positions
b=sqrt(16-a.^2);

syms xp yp
origin = [4 12 0 8 6 4 2 0 8 76];

validpts=double.empty(0,3);
count=0;
for iter=1:6
    ap=a(iter);
    bp=b(iter);
    if isreal(ap)&&isreal(bp)
        count=count+1;
        validpt=[origin(iter) ap bp];
        validpts=[validpts; validpt];
    end
end

figure('Name','For tag ID');

for iter=1:count
    f_new = @(xp,yp) ((yp-validpts(iter,1))^2/(validpts(iter,2)^2))-((xp)^2/(validpts(iter,3)^2))-1;

    hold on;
    fimplicit(f_new)

    xlim([-150 150]);
    ylim([-50 100]);
end

interpts=double.empty(0,2);
for x=-150:0.1:0
    for y=0:0.1:180
        for i=1:count
            for j=1:count
                if abs((((y-validpts(i,1))^2/(validpts(i,2)^2))-((x)^2/(validpts(i,3)^2))-1))<0.001
                    if abs((((y-validpts(j,1))^2/(validpts(j,2)^2))-((x)^2/(validpts(j,3)^2))-1))<0.001
                        interpts=[interpts; [x y]];
                    end
                end
            end
        end
    end
end

hold on;

idx = dbscan(interpts,3,3);
gscatter(interpts(:,1),interpts(:,2),idx,'kr','*');

Answer 1

[Chetan Bhavsar]

Error You are getting

Expected X to be nonempty

Because of variable

interpts

is empty.

and it is empty because it is never going either if statement.

                if abs((((y-validpts(i,1))^2/(validpts(i,2)^2))-((x)^2/(validpts(i,3)^2))-1))<0.001  
                    'First If check'
                    if abs((((y-validpts(j,1))^2/(validpts(j,2)^2))-((x)^2/(validpts(j,3)^2))-1))<0.001
                        'Second If check'
                        interpts=[interpts; [x y]];
                    end
                end

You can try debugging why its not entering this if.

lambda = 34.64; % in cm, considering 866MhZ frequency
pathData_1 = zeros(1,6);
PhData_1 =zeros(1,6);
for i=1:5
    theta=PhData_1(i+1)-PhData_1(i);
    thetaRad=pi*theta/180;
    pathData_1(i)=(thetaRad)*lambda/(4*pi);
end
a=pathData_1/2;
c=ones(1,6).*4; % fixed 8cm distance between two antenna positions
b=sqrt(16-a.^2);
syms xp yp
origin = [4 12 0 8 6 4 2 0 8 76];
validpts=double.empty(0,3);
count=0;
for iter=1:6
    ap=a(iter);
    bp=b(iter);
    if isreal(ap)&&isreal(bp)
        count=count+1;
        validpt=[origin(iter) ap bp];
        validpts=[validpts; validpt];
    end
end
figure('Name','For tag ID');
for iter=1:count
    f_new = @(xp,yp) ((yp-validpts(iter,1))^2/(validpts(iter,2)^2))-((xp)^2/(validpts(iter,3)^2))-1;
    hold on;
    fimplicit(f_new)
    xlim([-150 150]);
    ylim([-50 100]);
end

Warning: Function behaves unexpectedly on array inputs. To improve performance, properly vectorize your function to return an output with the same size and shape as the input arguments.

Warning: Function behaves unexpectedly on array inputs. To improve performance, properly vectorize your function to return an output with the same size and shape as the input arguments.

Warning: Function behaves unexpectedly on array inputs. To improve performance, properly vectorize your function to return an output with the same size and shape as the input arguments.

Warning: Function behaves unexpectedly on array inputs. To improve performance, properly vectorize your function to return an output with the same size and shape as the input arguments.

Warning: Function behaves unexpectedly on array inputs. To improve performance, properly vectorize your function to return an output with the same size and shape as the input arguments.

Warning: Function behaves unexpectedly on array inputs. To improve performance, properly vectorize your function to return an output with the same size and shape as the input arguments.

interpts=double.empty(0,2);
for x=-150:0.1:0
    for y=0:0.1:180
        for i=1:count
            for j=1:count
                if abs((((y-validpts(i,1))^2/(validpts(i,2)^2))-((x)^2/(validpts(i,3)^2))-1))<0.001  
                    'First If check'
                    if abs((((y-validpts(j,1))^2/(validpts(j,2)^2))-((x)^2/(validpts(j,3)^2))-1))<0.001
                        'Second If check'
                        interpts=[interpts; [x y]];
                    end
                end
            end
        end
    end
end
hold on;

interpts

interpts =

  0×2 empty double matrix

idx = dbscan(interpts,3,3);

Error using dbscan
Expected X to be nonempty.

gscatter(interpts(:,1),interpts(:,2),idx,'kr','*');

[Divya]

Okay, this helps. Thanks!