Search 1D Array not working with Double

[ssingh1]

Can anyone tell why Search 1D Array function is not working as expected in the attached VI ?

Message Edited by ssingh1 on 26-04-2010 08:21 PM

[smercurio_fc]

Please do a search on "equality", "LabVIEW", "floating point", "I found a bug in LabVIEW!", "LabVIEW can't do math!"

Also,  http://en.wikipedia.org/wiki/Floating_point#Accuracy_problems.

The Search 1D Array works by performing equality comparisons.

I have another nickel in my retirement fund.

[Norbert_B]

Search 1D Array uses an "equal" as comparation. It is always a bad idea to compare floating point numbers with equal.

There are plenty of threads on this forum covering this issue. (example here).

This is not a LV issue (see here).

hope this helps,

Norbert

[nathand]

The problem is the way floating-point numbers are represented in binary.  You can find many discussions on the subject of comparing two floating-point numbers on this forum.  One good explanation is at: http://digital.ni.com/public.nsf/allkb/B01682241DD825948625665100663F61

[Yamaeda]

Welcome to the world of floats and doubles. The precision is good, but not infinite giving these symptoms every so often.

[Yamaeda]

The VI is right, btw. Increasing visible number of decimals you'll notice you compare 0,58723354278 to 0,587234 which will never be true.

[Lucither · Accepted solution]

Hi Singh,

The 2 numbers you have arent equal:

Number in array is actually: 0.5872335427799636, you can see this by altering the display format.

Its to do with how the double value is stored on the computer.

I use an array called 'Approx Equals' that compares numbers to a specified decimal place:

I have attached the 'Approx Equals' vi. As said you can specify the accuracy of the comparison.

Rgs,

Lucither

[ssingh1]

Dear Friends,

Thank-you very much for your prompt replies explaining the reason for Search 1D Array not working accurately with doubles.

With regards
Shourya

Message Edited by ssingh1 on 27-04-2010 10:47 AM

[ssingh1]

Dear Friends,

Thank-you very much for your prompt replies explaining the reason for Search 1D Array not working accurately with doubles.

With regards
Shourya