I got "The expression to the left of the equals sign is not a valid target for an assignment."

Hello, when I run my code, i get error.

I can not see my fault. There is something wrong about i^2=-1 But I must use that expression.

Thank you.

clc
clear all
close all

fprintf('%10s %10s %10s %10s\n','k','real(xk)','imag(xk)','|f(xk)|')

k = 0 ;
i^2 = -1 ;
x = -2-2i;
f = @(x) x^3 - x - 3 ;

while abs(f(x)) > 10^(-5)
    f = @(x) x^3 - x - 3 ;
    diff = @(x) 3*(x^2) - 1 ; 
    xreal = real(x);
    ximag = imag(x);
    xnew = x - (f(x) / diff(x));
    fprintf('%10.4f %10.4f %10.4f %10.4f\n',k,xreal,ximag,f(x))
    x = xnew;
    
    
    k = k +1;
end

[A. Sawas]

In Matlab you don't need to define the imaginary number (i) or (j).

i^2 = -1 ; % this is not a valid assignment
x = -2-2i;

[hgrlk]

thank you!! i didnt know that

Answer 1

[Steven Lord]

Just eliminate that line from your code. The way you've defined x on the next line will make it complex since i is already defined to be the imaginary unit.

[hgrlk]

thank you!

Answer 2

[Kelly Kearney]

As others have pointed out, i is already assigned the value you want by default.

But assuming it weren't, the proper way to assign the value would be:

i = sqrt(-1);

The error is basically telling you that Matlab won't implictly do any algebra for you... you can only assign a value to a variable, not to a function or equation like you attempted to do.

[hgrlk]

thank youu