if statement problem with function

i'm given the task to create an if statement for this problem

i have an array from -1:1

x=[-1:0.1:1]

and a function f= x.^2.*sin(pi.*x)

and i'm supposted to make an if statement arround g

if F>=0 then g=F

if F<0 then g=0

the problem seems pretty easy to solve but somehow i can't seem to do it

i've coded this so far but i keep getting error messages and i don't understand why it's not working

i keep getting the error message: Index in position 2 is invalid. Array indices must be positive integers or logical values.

Error in solution (line 6)

if f(1,i) >= 0

x = [-1:0.1:1];

f = (x.^2).*(sin(pi.*x));

for i = -1:1
    if f(1,i) >= 0 
        g(1,i)=f
    elseif f(1,i)<0
        g(1,i)=0
    end
end

[Stephen23]

The MATLAB approach:

x = -1:0.1:1; % get rid of the superfluous brackets
f = x.^2.*sin(pi.*x);
g = max(0,f);

Answer 1

[Sudhakar Shinde]

This may help you:

x = [-1:0.1:1];
f = (x.^2).*(sin(pi.*x));
g=zeros(1,length(f));
for i = 1:length(f)
    if f(i) >= 0 
        g(i)=f(i);
    elseif f(i)<0
        g(i)=0;
    end
end

[Khadijat Chagayeva]

why did you add g=zeros(1,length(f)) before the loop?

[Sudhakar Shinde]

this is inialization of 'g'.

[Stephen23]

https://www.mathworks.com/matlabcentral/answers/35676-why-not-use-square-brackets