[Tutor] Do loop in Python

[stm atoc]

Thank you so much for your reply. It was very helpful information and
I used it in order to improve the program....

Here is the new version of the program:

zvalues = [-200]  # starting value
hvalues = [10]  # starting value
increments = [1, 1, 1, 1, 1, 1, 1, 1]
for N in increments:
       h = hvalues[-1] - N
       hvalues.append(h)
       z = zvalues[-1] + h
       zvalues.append(z)
       height = arange((z)*dz,0,dz)
       for z,when in enumerate(height):
           nuh.append(0.001 * exp(-0.005*(z+200.0))*dz) #turbulence
diffusivity m**2/s
           nu.append(num + nuh[z])

The story is like this:
I should define layers and thickness and see how the diffusion profile
changes over the z.
height (or depth) of the total thickness or 'z'.
I basically, define 'z' in 10 layers and each layer is called  ' N' .
Difference between each layer is 'h', which is equal 10 micrometer.
Now, what I like to do is the modification of nu based on each zvalue
In fact, for each 'zvalue' o'z' step, I need to calculate a different
value for 'nu' based on the available equation in the program.

BUT, I am not sure, exactly, how to add the new do loop of z inside
another loop of nu.

I have done this way as well (the other way around):

height = arange((z)*dz,0,dz)
for z,when in enumerate(height):
    for N in increments:
       h = hvalues[-1] - N
       hvalues.append(h)
       z = zvalues[-1] + h
       zvalues.append(z)
       nuh.append(0.001 * exp(-0.005*(z+200.0))*dz) #turbulence
diffusivity m**2/s
       nu.append(num + nuh[z])

but still no sign of 'nu changes' over 'z'!

So, would it be possible to check that again?

Thanks, Sue

On Fri, Nov 25, 2011 at 12:36 PM, Steven D'Aprano <steve at pearwood.info> wrote:
> stm atoc wrote:
>>
>> Hi there,
>>
>> I am a new python user.
>> I have  a question regarding  do loop.....
>>
>> This is a simple program that I have written:
>>
>> -----------------
>> N=10
>> h=10.0 # [micrometer]
>> z=-200.0 # [micrometer]
>
> You define N, h and z here, but later on you use them as loop variables. So
> these three values never get used: they are thrown away, and replaced by the
> values of the loops:
>
> h -> 0, 1, 2, ... 9
> N -> 0, 1, 2, ... 9
>
> z is especially troublesome, because it gets used for TWO loop variables,
> one inside the other. The inner z loop depends on the outer z loop, which
> makes it tricky to predict what values z will take.
>
>
>> num = 0.05 #m**2/s
>> dz = 1.0
>> nuh=[]
>> tmax=3600
>> dt=20.
>> nu=[]height = arange(z*dz,0,dz)
>
> What is arange?
>
> In physics, "height" is a scalar. But later on, you seen to use height as if
> it were a collection of values.
>
>
>> outfile=open('nu.dat','w')
>> outfile.write('height, nu, nuh')
>>
>> for z,when in enumerate(height):
>>   for h in range(10):
>>       for N in range(10):
>>           for z in range((N-z)+(N-h)):
>>
>>               nuh.append(0.01 * exp(-0.05*(z+200.0))*dz) #turbulence
>> diffusivity m**2/s
>>               nu.append(num + nuh[z])
>>
>> -----------------------
>> What I like to do with this program is do loop like the fortran
>> version of  as follows:
>>
>> do i = 2, N
>>  z(i) = z(i-1) +h(i-1)
>>
>> end do
>
>
> How is z initialised? What is h?
>
>
> I *think* you are trying to add a small increment to each value, based on
> the previous value. Am I close?
>
>
> Does this example help?
>
>
> zvalues = [1]  # starting value
> increments = [0.01, 0.01, 0.02, 0.01, 0.01, 0.02, 0.01, 0.01]
> for h in increments:
>    z = zvalues[-1] + h
>    zvalues.append(z)
>
> print(zvalues)
>
>
> (Note: beware of floating point rounding.)
>
>
>
>
> --
> Steven
>
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