I am starting to learn python and since I have had some programming before ( intro to java last semester and intro to c++ a couple years ago) the teacher gave me an interesting problem to solve. It is an equation called the Prandtl equation from fluid flow measurement it is 1/sqrt(f) = 2.0*log(Re*sqrt(f))-0.8 and the reason the Reynolds number needs to be above 4000 is because the flow must be turbulent for the Prandtl equation to apply to that system

I wrote a program that should(?) solve the equation relatively accurately but I can not get it to execute properly to find out if it works or not, the code is below and I am using pythonwin editor in my attempts to execute it

```
import math
print "this program solves the prandtl equation by iteration"
Re = input("please input the renolds number now")
if Re<4000:
print "not a valid entry"
else:
for i in range(1,11):
f= 0.054
A = 1/sqrt(f)
B = 2.0*log(Re*sqrt(f))-0.8
if A<B:
f = f-((f-0.008)/2)
i = i+1
elif B>A:
f= f+((0.1-f)/2)
i = i+1
else:
break
print "the friction factor is",f
```

the program will execute through accepting the Reynolds number but then it stops an error msg that says that sqrt is not defined since I imported the math library I am not sure what that is about

any ideas on what I am doing wrong?

thanks

oneill