Test of Approximately Equality

Hello,

I have a value b and c. b and c are approximatly equal (b~c). They have +-5% difference.

I want to test of approximately equality..like this:

if b~c (with +-5% difference)
return something...
end

Answer 1

[Jan]

You only have to decide if it should be 5% of the first or the second argument. Then:

if abs(b - c) < 0.05 * b

or

if abs(b - c) < 0.05 * max(b, c)

or

if abs(b - c) < 0.05 * min(b, c)

or

if abs(b - c) < 0.05 * (b + c) * 0.5

[Walter Roberson]

Some of those expressions will have difficulty if "b" is negative.

[Greg Heath]

1. Try using "abs" on the RHS

2. Might also consider median(abs(b),abs(c))

Greg

Answer 2

[Stephen Nagy]

Your desired goal isn't entirely clear, but depending on the outcome you seek, the functions "uniquetol" and some of its related functions might be helpful.

[Walter Roberson]

ismembertol() and uniquetol() did not exist in 2012 though ;-)

Answer 3

[per isakson]

See isalmost(a,b,tol) in the File Exchange. There are more.