You’re not subscripting either ‘x’ or ‘y’. That’s important because ‘x’ is negative and zero, so it can’t be used as indices. Also, the lengths of both vectors have to be the same.
A few tweaks and your code works:
e=2.718;
x=-2:1:6;
for k1 = 1:length(x)
if x(k1)<-1
y(k1)=e.^(x(k1)+1);
elseif x(k1)>=-1 && x(k1)<5
y(k1)=2+cos(pi.*x(k1));
elseif x>=5
y(k1)=10.*(x(k1)-5)+1;
else
fprintf('\nanswer not given\n')
y(k1) = NaN;
end
end
x=-2:6;
plot(x,y)
