i received an error (index must be a positive integer or logical. Error in Guassseidal3 (line 24) U(i,0)=0;) in solving PDE problems. plz help me to get out of this problem.

function U=Guassseidal(n,m,a,b,c,d,E,NO)

n=3;

m=3;

a=0;

b=3;

c=0;

d=3;

E=10^-3;

NO=1000;

h=(b-a)/n;

k=(d-c)/m;

for i=1:n-1

x(i)=a+i*h;

end

for j=1:m-1

y(j)=c+j*k;

end

for i=1:n-1

for j=1:m-1

U(i,j)=0;

end

end

for i=1:n-1

U(i,0)=0;

U(i,m)=0;

end

for j=1:m-1

U(0,j)=0;

U(n,j)=0;

end

K=1;

Alpha=2*(1+h*h/K*K);

while K<=NO

errchk=0;

for j=1:m-1

for i=1:n-1

S=(-h^2*(-10)+U(i-1,j)+U(i+1,j)+(0.5*Alpha-1)*(U(i,j-1)+U(i,j+1)))/Alpha;

end

if errchk<abs(S-U(i,j))

errchk=abs(S-U(i,j));

U(i,j)=S;

end

end

if errchk<=E

for j=1:m-1

for i=1:n-1;

output(u(i,j))

end

end

STOP

end

K=K+1;

end

Output('Maximum number of iteration exceed;procedure completed unsuccessfully');

STOP

Answer 1

[Alex Mcaulley]

0 is not a valid index in Matlab. To take the first element you should put 1:

U(i,1)=0;

[Zuhaa Naz]

but it moves outside the grid, by taking U(i,1)=0;