Can anyone help me to understand the logic of below code

Xb=Xm; Yb=Ym; Zb=Zm; % Boundary Points
Xf=[];Yf=[];Zf=[];

for z=min(Zb):1:max(Zb)+0.5
    x1=Xb(abs(Zb-z)<0.01);y1=Yb(abs(Zb-z)<0.01);z1=Zb(abs(Zb-z)<0.01);
    for y=min(y1):1:max(y1)+0.5
        x2=x1(abs(y1-y)<0.01);y2=y1(abs(y1-y)<0.01);z2=z1(abs(y1-y)<0.01);
        xf=x2(abs(x2-min(x2))<0.01); yf=y2(abs(x2-min(x2))<0.01);zf=z2(abs(x2-min(x2))<0.01);
        Xf=[Xf;xf];Yf=[Yf;yf];Zf=[Zf;zf];     
    end
end

range of Xb = 12.75 to 26.75

range of Yb = -10 to 10

range of Zb = -10 to 10

[Adam]

It would be a lot more readable with one instruction per line than 3 instructions per line. Also you haven't given any indication where the code comes from. It's a waste of time for us trying to understand the logic in unidentified 3rd party code - there's no guarantee it actually has any logic and isn't just garbage code!

[VANDANA GUPTA]

sorry sir... i am providing the full code for understand...

clc
clear variables
close all
theta=-pi/6:pi/180:pi/6;
phi=-pi/6:pi/180:pi/6;
[theta,phi]=meshgrid(theta,phi);
 %field which has non-uniform spacing grid
Xs=[ ];  Ys=[ ];  Zs=[ ];
for rho=5:0.5:50
    [x,y,z]=sph2cart(theta,phi,rho);
    mesh(x,y,z,'edgecolor','r','facecolor','none','edgealpha',0.05);  
     hold on
    Xs=[Xs;x(:)];
    Ys=[Ys;y(:)];
     Zs=[Zs;z(:)];
end
% uniform spacing grid
Xc=[ ];  Yc=[ ];  Zc=[ ]; 
dx=1;  dy=1;   dz=1;
for x=3.75:dx:50.4
    y=min(y(:)):dy:max(y(:));
    z=min(z(:)):dz:max(z(:));
    [y,z]=meshgrid(y,z);
    mesh(x*ones(size(y)),y,z,'edgecolor','g','facecolor','none','edgealpha',.1) 
    hold on
    Xc=[Xc;x*ones(size(y(:)))];
    Yc=[Yc;y(:)];
     Zc=[Zc;z(:)];
end
hold on
%  Cuboid shape of sample object on non-uniform grid
xo=Xs(abs(Xs-20)<=3&abs(Ys)<=2.5&abs(Zs)<=2);
yo=Ys(abs(Xs-20)<=3&abs(Ys)<=2.5&abs(Zs)<=2);
zo=Zs(abs(Xs-20)<=3&abs(Ys)<=2.5&abs(Zs)<=2);
k = boundary(xo,yo,zo);
trisurf(k, xo,yo,zo,'edgecolor','none', 'facecolor','b')
%  Mapping of the facets of object to the nearest point on uniform grid 
k1=dsearchn(Xc,xo);
k2=dsearchn(Yc,yo);
k3=dsearchn(Zc,zo);
Xm=Xc(k1);
Ym=Yc(k2); 
Zm=Zc(k3);
 plot3(Xm,Ym,Zm,'.k' )
%  Make boundary of outer facets with enclosing inner facets
k = boundary(Xm,Ym,Zm,1);
trisurf(k, Xm,Ym,Zm,'edgecolor','none','facecolor','m', 'facealpha',0.5)
%  Showing the front surface only where signals being reflected
Xb=Xm;  Yb=Ym;  Zb=Zm;     % boundary points
Xf=[ ];  Yf=[ ];  Zf=[ ];

% find the points in the front surface
for z=min(Zb):1:max(Zb)+0.5
     x1=Xb(abs(Zb-z)<0.01);
     y1=Yb(abs(Zb-z)<0.01);
     z1=Zb(abs(Zb-z)<0.01);
     for y=min(y1):1:max(y1)+0.5
         x2=x1(abs(y1-y)<0.01);
         y2=y1(abs(y1-y)<0.01);
         z2=z1(abs(y1-y)<0.01);
         xf=x2(abs(x2-min(x2))<0.01); 
         yf=y2(abs(x2-min(x2))<0.01);
         zf=z2(abs(x2-min(x2))<0.01);
         Xf=[Xf; xf];    Yf=[Yf; yf];   Zf=[Zf; zf];     
     end
 end
plot3(Xm,Ym,Zm,'.k' )
hold on
X1=[Xf(1), Xf(1),Xf(1),Xf(1)];
Y1=[min(Yf), min(Yf),max(Yf), max(Yf)];
Z1=[min(Zf), max(Zf),max(Zf), min(Zf)];
fill3(X1, Y1, Z1, 'r')

sir i want to understand the matlab code for making front surface..how ''abs(Zb-z)<0.01, abs(y1-y)<0.01, abs(x2-min(x2))<0.01'' these conditions work exactly in the code

[KALYAN ACHARJYA]

@Vandana Is their specific line or full code?

[VANDANA GUPTA]

sir this is the full code...

[VANDANA GUPTA]

sir, i want to understand this portion of this code:

% find the points in the front surface
for z=min(Zb):1:max(Zb)+0.5
     x1=Xb(abs(Zb-z)<0.01);
     y1=Yb(abs(Zb-z)<0.01);
     z1=Zb(abs(Zb-z)<0.01);
     for y=min(y1):1:max(y1)+0.5
         x2=x1(abs(y1-y)<0.01);
         y2=y1(abs(y1-y)<0.01);
         z2=z1(abs(y1-y)<0.01);
         xf=x2(abs(x2-min(x2))<0.01); 
         yf=y2(abs(x2-min(x2))<0.01);
         zf=z2(abs(x2-min(x2))<0.01);
         Xf=[Xf; xf];    Yf=[Yf; yf];   Zf=[Zf; zf];     
     end
 end

[Guillaume]

It calculates some stuff. Now, since you still haven't told us what the overall purpose of the code is, I doubt anybody is going to bother looking any deeper. Well written code would have comment explaining what the variables are (and have better variable names) and comments explaining what's going on. This hasn't

I suggest that if you need help understanding the code, you ask whoever wrote it.

Oh, and please use the toolbar to format the code as code. It's the button.

Answer 1

[Jan]

Start with a simplification of the code to make it easier to read:

% find the points in the front surface
for z = min(Zb):max(Zb) + 0.5
    % Get x, y, z values of points near to Zb==z:
    index = (abs(Zb - z) < 0.01); 
    x1    = Xb(index);
    y1    = Yb(index);
    z1    = Zb(index);
    for y = min(y1):max(y1) + 0.5
        % Get x1, y1, z1 values of points near to y1==y:
        index = (abs(y1-y) < 0.01);
        x2    = x1(index);
        y2    = y1(index);
        z2    = z1(index);
        
        % Get x2, y2, z2 values of points near to y2==min(x2):
        index = (abs(x2-min(x2)) < 0.01);
        xf    = x2(index); 
        yf    = y2(index);
        zf    = z2(index);
        
        % Collect the xf, yf, zf values:
        Xf = [Xf; xf];
        Yf = [Yf; yf];
        Zf = [Zf; zf];     
    end
 end

[VANDANA GUPTA]

ok, sir.......sir in the code of front surface, is vector size reduced of Xb,Yb and Zb upto x2, y2 and z2....and in xf, yf and zf, surface is getting

[Jan]

@VANDANA GUPTA: So do you have a specific question about the code?