Why it is saying this? Index in position 2 is invalid. Array indices must be positive integers or logical values. Error in Homework (line 21) surf(x,y,F(i,j))

x=[-5:5]

y=[-5:5]

for i=1:(x-1);

for j=1:(y-1);

if (x(i)>=0)&(y(j)>=0)

F(i,j)=2.*x(i)+y(j)^2

end

if (x(i)>=0)&(y(j)<0)

F(i,j)=x(i)+y(j)

end

if (x(i)<0)& (y(j)>=0)

F(i,j)=x(i)^2+2*y(j)

end

if (x(i)<0)&(y(j)<0)

F(i,j)=x(i)^2+y(j)^2

else

end

end

end

figure

surf(x,y,F(i,j))

Answer 1

[Alan Stevens]

Like this

x=[-5:5];
y=[-5:5];
for i=1:numel(x)
    for j=1:numel(y)
if (x(i)>=0)&&(y(j)>=0)
    F(i,j)=2.*x(i)+y(j)^2;
end
if (x(i)>=0)&&(y(j)<0)
        F(i,j)=x(i)+y(j);
end
if (x(i)<0)&& (y(j)>=0)
         F(i,j)=x(i)^2+2*y(j);
end
if (x(i)<0)&&(y(j)<0)
                F(i,j)=x(i)^2+y(j)^2;
else
end
    end
end
figure
surf(x,y,F)

[Akash Talapatra]

why is this numel written within for loop? would you like to explain this a little bit?

[Alan Stevens]

numel(x) means the number of elements in x. Your statements like

for i=1:(x-1);

don't make sense.