I'm totally stuck with a math problem and though I should  ask the list=20
for help as a last resort

I need to calculate the dew point in C using integer maths. The dew=20
point can be calculated with the following expression

logEw =3D ( 0.66077 + ( ( 7.5 * T )  /  (237.3 + T ) ) + ( log10(RH) - 2 =
)
dp =3D ( (0.66077 - logEw ) * 237.3 )  /  ( logEw - 8.16077  )

which is derived from

EW =3D 10^ ( 0.66077+(7.5*T/ (237.3+T)) )     //  this is the saturation=20
vapor pressure over water.
EW_RH =3D EW * RH / 100                             // multiply with=20
relative humidity
Dp =3D ((0.66077-log10(EW_RH))*237.3)  / (log10(EW_RH)-8.16077) // this i=
s=20
the dewpoint

My usual approach to this is to try to make everything in the expression=20
integers so I end up with a result that is a number of factors bigger=20
than the actual and that way preserving decimals. But in this case an=20
long is to small for such an approach.

I can get the ( log10(RH) - 2 ) expression from a table.

My input values for T and RH is t =3D 100*T and rh =3D 100 * RH that is b=
oth=20
is preserved with two decimals.

Any suggestions appreciated....

Regards
/Ake



--=20
 ---
Ake Hedman (YAP - Yet Another Programmer)
eurosource, Brattbergav=E4gen 17, 820 50 LOS, Sweden
Phone: (46) 657 413430 Cellular: (46) 73 84 84 102
Company home: http://www.eurosource.se     =20
Kryddor/Te/Kaffe: http://www.brattberg.com
Personal homepage: http://www.eurosource.se/akhe
Automated home: http://www.vscp.org

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body