Data must be a single matrix Y or a list of pairs X,Y

My aim is to plot 2d the function ph (xx,yy) in the plane (xx,yy).

x-axis is xx, y-axis is yy, and the function ph(xx,yy)

=====================================================

q=1.0;
v=(1.0-sqrt(1.0+4.0*q))/(2.0*q);
p=4*atan(1.0);
for j=0:100
    a=0.0+j.*p/100;
    fori=0:100
    b=0.0+i.*p/100;
    x=cos(a);
    y=sin(b);
    z=x.*x+y.*y;
    if z<1.0
        xx=x;
        yy=y;
        zz=z;
        D=1.0+q.*(v.*v)*(zz.*zz);
        N=1.0-v.*zz-q.*(v.*v)*(zz.*zz);
        ph=D/N;
        
        hold on
        plot(xx,yy,ph)
    end 
end 
end 

=====================================

[VBBV]

@Khaled you can try with fimplicit function

Answer 1

[Mathieu NOE]

hello

maybe this ?

I prefer to avoid using i and j as loop indexes as those letters usually are reserved as the iamginary unit in matlab (so I took cj and ci )

index start at 1 and not 0 in matlab

then there was a uncovered condition in this loop : if z<1.0 you need to define what should be ph if this condition is not met

clc
clearvars
q=1.0;
v=(1.0-sqrt(1.0+4.0*q))/(2.0*q);
 p=4*atan(1.0);
 
for cj=1:100
    a=0.0+cj.*p/100;
    x=cos(a);
    xs(cj) = x; % store current x value in array xs
    for ci=1:100
       b=0.0+ci.*p/100;
        y=sin(b);
        ys(ci) = y;% store current y value in array ys
        z=x.*x+y.*y;
         if z<1.0
            xx=x;
            yy=y;
            zz=z;
           D=1.0+q.*(v.*v)*(zz.*zz);
           N=1.0-v.*zz-q.*(v.*v)*(zz.*zz);
           ph(cj,ci)=D/N;
         else  % /!\ was missing 
             ph(cj,ci)= z ; % <== put the correct value here
         end
         
     end 
end

 surf(xs,ys,ph)

●

[Khaled]

Dear sir,

Thank you very much. It works now but it is still in 3d.

I want it in 2d like this figure:

[Mathieu NOE]

this looks like an implicit equation f(x,y) = 0

what does ph means here ?

can yu share the publication or docuent you are working from

[Khaled]

The equation :

[Mathieu NOE]

ok so now we understand z² = x²+y² <1 and it's indeed an implicit function to solve but I am still not sure what ph is supposed to be (a constnat value) ?

[Khaled]

Yes sir, It seems that

[Mathieu NOE]

can you share a little bit more than just these lines

[Mathieu NOE]

@Khaled

problem solved finally ?

[Khaled]

Dear Sir, Unfortunately, it is still not solved in 2D. !

[Mathieu NOE]

what is the name of this curve ? can you share the publication or book page you are working on ?

Answer 2

[VBBV]

hold on
q=1.0;
v=(1.0-sqrt(1.0+4.0*q))/(2.0*q);
 p=4*atan(1.0);
for j=0:100
    a=0.0+j.*p/100;
        for i=0:100
       b=0.0+i.*p/100;
 x=cos(a);
y=sin(b);
 z=x.*x+y.*y;
 if z<1.0
    xx=x;
    yy=y;
    zz=z;
   D=1.0+q.*(v.*v)*(zz.*zz);
 N=1.0-v.*zz-q.*(v.*v)*(zz.*zz);

 ph=D/N;
   
   % hold on
 plot3(xx,yy,ph,'bo')
     end 
  end 
end

%surf(xx,yy,ph)
     %v=(1.0-sqrt(1.0+4.0*q))/(2.0*q); p=4*atan(1.0);for j=0:100  a=0.0+j.*p/100;      fori=0:100     b=0.0+i.*p/100; x=cos(a);y=sin(b); z=x.*x+y.*y; if z<1.0  xx=x;  yy=y;  zz=z; D=1.0+q.*(v.*v)*(zz.*zz); N=1.0-v.*zz-q.*(v.*v)*(zz.*zz); ph=D/N;   hold on plot(xx,yy,ph)end    end   end 

[Khaled]

Dear sir,

Thank you, but it is still what we need.

It should be like this

[VBBV]

@Khaled you can try this with some minor changes

hold on
q= 1; %linspace(0,1.0,5);
v=(1.0-sqrt(1.0+4.0*q))./(2.0*q);
k = 1;
 p=4*atan(1.0);
for j=0:100
    a=0.0+j.*p/180;  % check 
        for i=0:100
       b=0.0+i.*p/180;  % check
 x=cos(a);
y=sin(b);
 z=x.*x+y.*y;
 if z<1.0
    xx(k)=x;
    yy(k)=y;
    zz=z;
   D=1.0+q.*(v.*v)*(zz.*zz);
 N=1.0-v.*zz-q.*(v.*v)*(zz.*zz);

 ph(k)=(D)./N;
   k = k+1;
     
     end 
  end 
end
plot(xx(:),(ph(:)),'bo'); 

●

[Khaled]

Great thanks Sir,

but it is still not what we want !

[Khaled]

Yes sir,

I have spent a lot of time working on it using implicit! But all the tries fail!

[VBBV]

@Khaled the question is not clear with missing details. i can guess in this case, that x and y values need to checked in each loop itreation.

hold on
q= 1; %linspace(0,1.0,5);
v=(1.0-sqrt(1.0+4.0*q))./(2.0*q);
k = 1;
 p=4*atan(1.0);
for j=0:200
    a=0.0+j.*p/180;  % check 
        for i=0:0.5:100
       b=0.0+i.*p/180;  % check
 x=cos(3*b);
 y=cos(b);
 z=x.*x+y.*y;
 if z<1.0
    xx(k)=x;
    yy(k)=y;
    zz=z;
   D=1.0+q.*(v.*v)*(zz.*zz);
 N=1.0-v.*zz-q.*(v.*v)*(zz.*zz);

 ph(k)=(D)./N;
   k = k+1;
     
     end 
  end 
end
plot(-xx(:),(ph(:)),'bo'); xlim([-0.25 0.25])

%q= 1; %linspace(0,1.0,5);v=(1.0-sqrt(1.0+4.0*q))./(2.0*q);k = 1; p=4*atan(1.0);for j=0:100  a=0.0+j.*p/180;  % check       for i=0:100     b=0.0+i.*p/180;  % check x=cos(a);y=sin(b); z=x.*x+y.*y; if z<1.0  xx(k)=x;  yy(k)=y;  zz=z; D=1.0+q.*(v.*v)*(zz.*zz); N=1.0-v.*zz-q.*(v.*v)*(zz.*zz); ph(k)=(D)./N; k = k+1;      end end endplot(xx(:),(ph(:)),'bo');