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-   -   CFX Post Expressions number decimals (http://www.cfd-online.com/Forums/cfx/126958-cfx-post-expressions-number-decimals.html)

 njiang November 29, 2013 15:48

CFX Post Expressions number decimals

Hi, there,

I am creating an expression in CFX post using the trendline created in the Excel as following:

(-798936626.593750*z^6/1[m^6] + 4687121164.076870*z^5/1[m^5] - 11450097996.080200*z^4/1[m^4] + 14908481102.838800*z^3/1[m^3] - 10912008484.852500*z^2/1[m^2] + 4256979247.793130*z/1[m] - 691537634.412929)*1[K]

when I evaluate the expression using 0.91 for z, the CFX gives me wrong number 1536K, while Excel is 762K.

How do I change the decimal setup/precision in CFX?

Thanks.

Nan

 ghorrocks November 30, 2013 05:40

When you start the solver select double precision. But I vaguely recall that CEL is evaluated in single precision even with the rest of the numerics being double precision. I am not certain of this, but keep it is mind.

 njiang November 30, 2013 09:29

Hi, Glenn,

Thanks. I do have double precision turned on for solver.

 mvoss December 13, 2013 05:39

maybe you can use the "function"-function from cfx pre to overcome the rounding errors if the expression is supposed to be used in the simulation.
Be very careful about the resolution of the points being used in the function, because they will be interpolated piece-wise between two points.
You can also import data (like *.csv) for comparison in post - directly within the graph-tool.

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