## Improving accuracy of computation

on 7 Sep 2011

### Titus Edelhofer (view profile)

I'm doing an assignment for a class in numerical computation which involves calculating pi with a given formula. No problem there, however I'm also asked to improve accuracy by rewriting said formula.
I have to admit I have no idea what affects accuracy in matlab, especially when it's something as seemingly simple sa rewriting a relatively uncomplicated formula.
I'm wondering if anyone has any tips or examples for me, to help me understand how I can approach this. I haven't bothered posting the formula, since I'm really not after anyone giving me the solution, but rather understanding the question. :)

### Tags ### Titus Edelhofer (view profile)

on 7 Sep 2011

Most often numerical accuracy is (badly) affected when subtracting values of similar size. Example (using 4 digits only):
x1 = 1.234
x2 = 1.223
x = x1-x2 = 0.011
So: two numbers with 4 digits accuracy lead to a x with only two digits. Increasing accuracy is possible in those cases, where rearranging the formula leads to expressions avoiding the problem above....
Titus 