In regard to contour error

uhm.. it is so long. but i want to receive advice

 x=25:50;
nx=length(x)
y=25:50;
ny=length(y)
h=1;
for i=25:50
    for j=25:50
        v(i,j)=0;
        npbc(i,j)=0;
        roh(i,j)=0;
        perm(i,j)=8.854e-12;
    end
end
for i=25:50 
     npbc(i,25)=2;
end
for j=25:50
     npbc(i,1)=3;
end
for j=25:50
     v(50,j)=0;
     npbc(50,j)=1;
end
for i=25:50
    v(i,50)=100;
    npbc(i,50)=1;
end
v(50,50)=50;
npbc(50,50)=1;
k=0;
eps=1.e-07;
alpha=1.5;
reler=eps+1;
while reler>eps
    k=k+1
    vsum=0;
    chgsum=0;
    for i=25:50
        for j=25:50
            id=npbc(i,j);
            if id ==1, continue, end
            old=v(i,j);
            switch id
                case 0
                    v1=v(i-1,j);
                    v2=v(i+1,j);
                    v3=v(i,j-1);
                    v4=v(i,j+1);
                case 2
                    v1=v(i+1,j);
                    v2=v(i+1,j);
                    v3=v(i,j-1);
                    v4=v(i,j+1);
                case 3
                    v1=v(i-1,j);
                    v2=v(i+1,j);
                    v3=v(i,j+1);
                    v4=v(i,i+1);
                otherwise
                    v1=v(i+1,j);
                    v2=v(i+1,j);
                    v3=v(i,j+1);
                    v4=v(i,j+1);
            end
            v(i,j)=(v1+v2+v3+v4+h*h*roh(i,j)/perm(i,j))/4;
            chg=v(i,j)-old;
            v(i,j)=old+alpha*chg;
            chgsum=chgsum+abs(chg);
            vsum=vsum+abs(v(i,j));
        end
    end
    reler=chgsum/vsum;
end
%
contour(x,y,v,30)
xlabel('x')
ylabel('y')

Error using contour (line 81) The size of X must match the size of Z or the number of columns of Z.

Error in FDM_laplace_matlab11111 (line 75) contour(x,y,v,30)

Answer 1

[Martin Schätz]

Your size of v is 50x50, and you want to get element 51 (v2=v(i+1,j) and i=50). If you want to use code as that you have to change end of your for cycle to 49.

Also contour needs X Y and Z as 2D matrix. Check the contour help for examples.