Script adapted into a funtion Function not returning equal values

Hey everyone,

I'm having a problem where two identical pieces of code are returning different values when run as a script then a function. Trying to keep this as simple as possible, I have two vectors Z and Zt, which represent curves with a number of prominent peaks. I find the peak locations of each curve, then compare their separation distance using an adapted Gaussian function:

        1 - exp( (-mu0*Phi(ii)) / (2 * vp^2));

This is an extract from a loop, where Phi contains the difference between each peak of Z and Zt. mu0 and vp won't particularly matter here.

In particular, I have Z and Zt set so that their peak locations are in exactly the same place - and as a result the expression above will be

1 - exp(0) = 0;

for all entries in Phi.

This is exaclty what I want, but when I run this with a function call, it is returning very small values of order 10^-5, instead of zero.

Anyone have any ideas of why this may be?

Answer 1

[Geoff]

Floating point precision errors. If you need to test for zero, then test for something like:

if abs(value) < 1e-5

10^-5 does sound rather large for a zero value though.. Are you using single-precision floats?

[C Meek]

I'm using double precision. Turns out that the unexpected small numbers were coming from another part of my code which I hadn't taken into account - so all is well, when I adapt it according zero is returned ok!

Thanks