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August 31st, 2010, 08:49 AM   #1
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Logarithms and Reversing them

Not sure if this is the right area.... been out of math for awhile.

Log10(P) =( A - (B / T) - (C * Log10(T)) + (D * T) + (( E * (F - T)) / F * T) * Log10(F - T))

Formula for r22 temperature to pressure conversion
Where if T = 50 then P = 85 (rounded)

Now I am trying to reverse it to Get T from P, according to Antoine Equation for pressure temperature relations T = (B / (A - Log10(P))) - C

But I can't figure out the rest of the reverse equation to get the Temperature from the Pressure

A = 29.35754453
B = 3845.1931152
C = 7.86103122
D = 0.002190939044
E = 305.8268131
F = 686.1

This are the Fixed Coefficients for the Whole Calculations if anyone needs them...

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August 31st, 2010, 11:24 AM   #2
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Re: Logarithms and Reversing them

There isn't going to be any nice inverse formula. I'm not even sure if you could solve it explicitly with Lambert's W. The best way would be with a numerical method like the secant method or Brent's method.
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August 31st, 2010, 08:59 PM   #3
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Problem already posted and replied to here: viewtopic.php?f=13&t=15557
so topic locked.
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