Why am I getting the error of "Array indices must be positive integers or logical values." in the f(x) line?

clear; clc

x = -1.612 : 0.01 : -1.322 ;
for n = 1:1:length(x)
      f(x) = 8 * x(n)^3 - 2 * x(n)^2 - 15 * x(n) + 11 ;
      g(x) = -10 * x(n)^3 + 10 * x(n) - 13 ;
end
figure(1)
plot(x,f(x), x,g(x))

Answer 1

[madhan ravi]

Why on Earth do you need a loop?

x = -1.612 : 0.01 : -1.322 ;
f = 8 * x.^3 - 2 * x.^2 - 15 * x + 11 ;
g = -10 * x.^3 + 10 * x - 13 ;
figure(1)
plot(x, f, x, g)

[Gina Jarid]

I was asked to make it into a loop.

[madhan ravi]

x = -1.612 : 0.01 : -1.322 ;
[f, g] = deal(zeros(size(x)));
for n = 1 : numel(x)
      f(n) = 8 * x(n)^3 - 2 * x(n)^2 - 15 * x(n) + 11 ;
      g(n) = -10 * x(n)^3 + 10 * x(n) - 13 ;
end
figure(1)
plot(x, f, x, g)

[Gina Jarid]

Thanks this works, but I was told with the given info to begin my for-loop like this

So your for loop would begin:

x = [-1.612 : 0.01 : -1.322] ;

for n = 1 : 1 : length(x)

f(x) = 8*x(n)^3 ...

g(x) = -10*x(n)^3 ...

[madhan ravi]

Explain to your teacher/professor preallocation is important , while using a loop.

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html