Method to plug in a value

I am currently working on a bracketing algorithem (specifically false position for finding roots).

My issue is that the equation will be imputed as ways such as (x+(4*x^8)).

I need to be able to plug in the variables x_i and x_u into that equation as a susbtitute for x?

What would be the primary way I should go about doing this in a loop?

[dpb]

W/o seeing far more of code I'd guess just write an anonymous function and call it with the desired input...

fnF=@(x) x+4*x.^8;

If it's always some form of a polynomial, one could also just set the coefficients vector and call polyval

b=[4 0 0 0 0 0 0 1 0];   % 4x^8 + x 
F=polyval(b,x);

Answer 1

[Thiago Henrique Gomes Lobato]

I would agree with dpb that the best way is to use anonymous functions, the only thing that you additionally need is to be able to convert the user input to the function. A way to do it is with the eval function:

Equation = 'x+4*x.^8';
fnF= eval(['@(x)',Equation])
fnF =

  function_handle with value:

    @(x)x+4*x.^8

Answer 2

[Arramis]

how to enter and into mat lab as the equation u=x+y