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FormulaCalc with Waveform Channels
Tim Welters
Member
03-16-2007 07:18 AM
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I'm using DIADEM 10.0 and observe the following problem:
Calling "FormulaCalc" like this in a script:
R1=<Some constant != 0>
Call FormulaCalc("Ch('Group/NewChannel):= Ch('Group/WaveformChannel1')-Ch(''Group/WaveformChannel2')/R1")
Call FormulaCalc("Ch('Group/NewChannel):= Ch('Group/WaveformChannel1')-Ch(''Group/WaveformChannel2')/R1")
with "WaveformChannel1" and "WaveformChannel2" being waveform-channels, I expect "NewChannel" to be a waveform-channel, too.
But in some cases the result channel is returned as numeric channel, in some as waveform-channel.
Both input-channels have the same "waveform x-offset" (e.g. -0.0169000000000023) and nearly the same "waveform x-step width"
(e.g. 5.00000000000153E-06 and 4.99999999999996E-06 with the difference resulting from roundoff errors).
(e.g. 5.00000000000153E-06 and 4.99999999999996E-06 with the difference resulting from roundoff errors).
Is someone able to explain, what the criteria are to get a waveform channel as result of the calculation?
Any help is welcome!
Tim
Brad_Turpin
Trusted Enthusiast
03-19-2007 02:16 PM
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Hi Tim,
You've pretty much diagnosed the situation. If you manually change the "Waveform x-step width" property for both waveform channels in the Data Portal to the average of their two values (5E-06) so that they both have identical waveform properties, the FormulaCalc() operation will product a new waveform channel. If either the waveform time offset or waveform delta time properties are even slightly different, the resulting channel is a numeric channel.
Ask if you have questions about setting the property,
Brad Turpin
DIAdem Product Support Engineer
National Instruments
Christian_S
NI Employee (retired)
03-21-2007 04:30 AM
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Hi Tim,
Let me add one comment to Brad's explanation:
You can test the "equality" of two floating point numbers in the following way:
Call FormulaCalc("B1 := 5.00000000000153E-06 = 4.99999999999996E-06")
Call MsgBox(B1) ' false
Call FormulaCalc("B1 := 5.000000000000153E-06 = 4.99999999999996E-06")
Call MsgBox(B1) ' true
' DIAdem 10.1 or higher
If ProgramRevision >= 1010 Then
Call MsgBox(ValEqual(5.00000000000153E-06, 4.99999999999996E-06)) ' false
Call MsgBox(ValEqual(5.000000000000153E-06, 4.99999999999996E-06)) ' true
End If
You will see that DIAdem uses approx. 13 significant figures for the comparism.
Christian
