Attempted to access U(2,0); index must be a positive integer or logical.

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Zuhaa Naz 2020-3-6

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/509447-attempted-to-access-u-2-0-index-must-be-a-positive-integer-or-logical

编辑： Walter Roberson 2020-3-6

here is my Guass-seidal program for poisson equation, how will i overcome this error.

function U=Guassseidal(n,m,a,b,c,d,tol,N)
n=3; %input('enter the value of n=  ');
m=3; %input('enter the value of m=  ');
a=0; % input('enter the value of a=  ');
b=3; %input('enter the value of b=  ');
c=0; %input('enter the value of c=  ');
d=3; %input('enter the value of d=  ');
tol=0.001; %input('enter the value of tolerance=  ');
N=2; %input('enter the total number of iterations =  ');
A=-10; %input('input F(x,y)::::if your fuction is variable use inline('') ');  
Bc1=0;%input('enter the Boundary condition at U(x,c) ');
Bc2=0;%input('enter the Boundary condition at U(x,d) ');
Bc3=0;%input('enter the Boundary condition at U(a,y) ');
Bc4=0;%input('enter the Boundary condition at U(b,y) ');
h=(b-a)/n;
k=(d-c)/m;
for i=1:n-1
for j=1:m-1
    x(i)=a+i*h;
    y(i)=c+j*k;
end
end
for i=1:n-1
for j=1:m-1
    U(i,j)=0;
end
end
for i=2:n-1
        U(i,c)=Bc1;
        U(i,d)=Bc2;
 for j=1:m
            U(a,j)=Bc3;
            U(b,j)=Bc4;
end
end
        alpha=2*(1+h^2/k^2);
        K=1;
        while K<=N 
            errchk=0;
         for j=2:m-3
                for i=2:n-3
                    S=((-h^2)*A+U(i-1,j)+U(i+1,j)+(0.5*alpha-1)*(U(i,j-1)+U(i,j+1)))/alpha;
                    if errchk<abs(S-U(i,j))
                        errchk=abs(S-U(i,j));
                        U(i,j)=S;
                        if errchk<=tol
                        end
                            for j=1:m-1
                                for i=1:n-1
     disp(U)                           
     disp('succesfully complete with solution ')
     
                        end
                    end
                end
         end
    K=K+1;
        end
        disp('number of iterations exceed, unsuccessful completion')
        end
        
end
        
     
    