Trouble Replicating a Do Loop Structure

pwr · Post by **pwr** » Sat Jun 06, 2009 3:08 am

I am trying to convert an existing program and have the following Revolution function.

function s1_pT p, T
--
--Release on the IAPWS Industrial formulation 1997 for the Thermodynamic Properties of Water and Steam, September 1997
--5 Equations for Region 1, Section. 5.1 Basic Equation
--Eqution 7, Table 3, Page 6
--
put 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 8, 8, 21, 23, 29, 30, 31, 32 into I1
put -2, -1, 0, 1, 2, 3, 4, 5, -9, -7, -1, 0, 1, 3, -3, 0, 1, 3, 17, -4, 0, 6, -5, -2, 10, -8, -11, -6, -29, -31, -38, -39, -40, -41 into J1
put 0.14632971213167, -0.84548187169114, -3.756360367204, 3.3855169168385, -0.95791963387872, 0.15772038513228, -0.016616417199501, 8.1214629983568E-04, 2.8319080123804E-04, -6.0706301565874E-04, -0.018990068218419, -0.032529748770505, -0.021841717175414, -5.283835796993E-05, -4.7184321073267E-04, -3.0001780793026E-04, 4.7661393906987E-05, -4.4141845330846E-06, -7.2694996297594E-16, -3.1679644845054E-05, -2.8270797985312E-06, -8.5205128120103E-10, -2.2425281908E-06, -6.5171222895601E-07, -1.4341729937924E-13, -4.0516996860117E-07, -1.2734301741641E-09, -1.7424871230634E-10, -6.8762131295531E-19, 1.4478307828521E-20, 2.6335781662795E-23, -1.1947622640071E-23, 1.8228094581404E-24, -9.3537087292458E-26 into n1
put 0.461526 into R --kJ/(kg K)
put p / 16.53 into myPi
put 1386 / T into tau
put 0 into gamma
put 0 into gamma_der_tau
repeat with i = 1 to 34
put gamma_der_tau + (n1 * (7.1 - myPi) ^ I1 * J1 * (tau - 1.222) ^ (J1 - 1)) into gamma_der_tau
put gamma + n1 * (7.1 - myPi) ^ I1 * (tau - 1.222) ^ J1 into gamma
end repeat
put R * tau * gamma_der_tau - R * gamma into s1_pT
return s1_pT
end s1_pT

The problem I'm seeing is that the variables gamma and gamma-der_tau never change from the initialized zero value.

Can anyone tell me why? Is there a problem with my use of the 'repeat' control structure, or is the problem with the way I've initialized my arrays? Is the first array index 0 or 1? Something else????

WaltBrown · Post by **WaltBrown** » Sat Jun 06, 2009 3:13 am

Try
add (n1 * (7.1 - myPi) ^ I1 * J1 * (tau - 1.222) ^ (J1 - 1)) to gamma_der_tau
add (n1 * (7.1 - myPi) ^ I1 * (tau - 1.222) ^ J1) to gamma

Walt

mwieder · Post by **mwieder** » Sat Jun 06, 2009 7:58 am

The problem is that you're loading the data into a variable and then treating it like an array. To convert the variable lists to arrays, insert the following statements before the repeat loop:

Code: Select all

    split n1 by comma
    split I1 by comma
    split J1 by comma

(also, you'll probably confuse the compiler at some point if you define your return value name the same as your function name. You have to do this in Basic, and I assume that the original source is Basic for this reason, but it's better practice anywhere else to call your return value tReturn or something similar...)

bn · Post by bn » Sat Jun 06, 2009 10:59 am

pwr,
alternatively you could stick to the comma delimited item list you created (you did not create an array as Mark said) in the variables by changing your repeat loop:

Code: Select all

 repeat with i = 1 to 34
    put (item i of I1) * (item i of J1) into and so on
 end repeat

regards
Bernd

edited: previous version said variable where it should have said array