Decimal places for value stored

Hello, im wondering if there any way i could perform calculation using values up to 4 decimal places only.

For example,i write this in command windows:

x=4.21;
h=0.001;
f=@(x) x^3 + 8*x^2 + 23*x +3;
f2_prime = (f(x+h)-2*f(x)+f(x-h))/(h^2);

how can i make the value of f(x), f(x+h) and f(x-h) to be only up to 4 decimal places when calculating for f2_prime?

Answer 1

[Ameer Hamza]

You can use round()

x=4.21;
h=0.001;
f=@(x) x^3 + 8*x^2 + 23*x +3;
f2_prime = (round(f(x+h),4)-2*f(x)+round(f(x-h),4))/(h^2);

[fikri osman]

thank you, i will try and see if it works

[fikri osman]

f2_prime = (round(f(x+h),4)-2*f(x)+round(f(x-h),4))/(h^2);

does this round off the f(x) too?

[fikri osman]

f2_prime = (round(f(x+h),4)-(2*round(f(x),4)+round(f(x-h),4)/(h^2);

i use this and got error

[fikri osman]

f2_prime = (round(f(x+h),4)-2*round(f(x),4)+round(f(x-h),4))/(h^2);

i used this and got the answer i wanted, thank you sir

Answer 2

[Walter Roberson]

how can i make the value of f(x), f(x+h) and f(x-h) to be only up to 4 decimal places when calculating for f2_prime?

You would need to use fixed-point arithemetic, such as from the Fixed Point Toolbox.

A close second would be to use the Symbolic Toolbox with digits(4), but it turns out that the Symbolic Toolbox uses "guard digits" ... I think I read once that it uses 5 guard digits -- and the minimum permitted is digits(2)