Stumped on basic problem with floating point math

[josborne]

I can't figure this out!  It should be sooooo simple. 

Here is the challenge: 

I have an incoming time array.  For example:     0, 1, 2, 3, 4, 5, 6, 7, 8, 9

I want to scale this array by a constant (e.g. multiply by 0.1).  So the resulting array should be:     0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9

Then I want to calculate the difference between each and every subsequent element in the array.  In this example, the difference should 0.1 between every element.  But my comparison fails. 

See the example below.  As far as I can see, the resulting boolean should always be TRUE.  But its not.

But if I remove the scaling operation, then it works ok!

Please help!

[Darin.K · Accepted solution]

It has been awhile since smercurio has had a contribution to his retirement fund, but once again you have "discovered" that there is no exact binary representation for 0.1.

I'd use one of the current "almost equals" comparisons described here:

http://forums.ni.com/t5/LabVIEW/Darin-s-Weakly-Nugget-2-8-11/m-p/1444262

And vote for this if you haven't already:

http://forums.ni.com/t5/LabVIEW-Idea-Exchange/quot-Almost-Equal-quot-functions-for-Float-comparisons...

[smercurio_fc]

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@Darin.K wrote:

It has been awhile since smercurio has had a contribution to his retirement fund, but once again you have "discovered" that there is no exact binary representation for 0.1.

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Yeah, the little piggy was getting a little light.

josborne, you owe me a nickel.

[NIquist]

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@smercurio_fc wrote:

josborne, you owe me a nickel.

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Don't you mean two bits???