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Creating a Program to Decompose a Number and Run a Function on that Decomposition

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  Creating a Program to Decompose a Number and Run a Function on that Decomposition CTSB01 <scott.moore270@gmail.com> - 2013-07-17 16:58 -0700
    Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition Joshua Landau <joshua@landau.ws> - 2013-07-18 10:12 +0100
      Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition CTSB01 <scott.moore270@gmail.com> - 2013-07-18 14:57 -0700
        Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition Gary Herron <gherron@digipen.edu> - 2013-07-18 15:12 -0700
          Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition CTSB01 <scott.moore270@gmail.com> - 2013-07-18 15:18 -0700
            Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition Ian Kelly <ian.g.kelly@gmail.com> - 2013-07-18 16:49 -0600
              Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition CTSB01 <scott.moore270@gmail.com> - 2013-07-18 16:04 -0700
                Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition Ian Kelly <ian.g.kelly@gmail.com> - 2013-07-18 17:42 -0600
                Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition Ian Kelly <ian.g.kelly@gmail.com> - 2013-07-18 17:45 -0600
                  Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition CTSB01 <scott.moore270@gmail.com> - 2013-07-18 17:25 -0700
                Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition "Rhodri James" <rhodri@wildebst.demon.co.uk> - 2013-07-19 00:48 +0100
                Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition Dave Angel <davea@davea.name> - 2013-07-18 19:49 -0400
                  Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition CTSB01 <scott.moore270@gmail.com> - 2013-07-18 17:35 -0700
                    Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition Dave Angel <davea@davea.name> - 2013-07-18 21:04 -0400
                      Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition CTSB01 <scott.moore270@gmail.com> - 2013-07-18 19:16 -0700
                        Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition Dave Angel <davea@davea.name> - 2013-07-18 22:43 -0400
                          Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition CTSB01 <scott.moore270@gmail.com> - 2013-07-18 19:56 -0700
                        Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition Fábio Santos <fabiosantosart@gmail.com> - 2013-07-19 03:48 +0100
                          Re: Creating a Program to Decompose a Number and Run a Function on that Decomposition CTSB01 <scott.moore270@gmail.com> - 2013-07-18 19:54 -0700

#50811 — Creating a Program to Decompose a Number and Run a Function on that Decomposition

I've been puzzling over how to get a certain function working in Python. The function, takes positive integers to other positive integers as follows:

    Phi_m(n2) = Phi_m(m*n + r) = m*x[n1] + r*(x[n1 + 1] - x[n1])

The above terms are all integer valued and are defined as follows:

    n2 = the (n2)th slot of the output string
    
    m = a fixed positive integer
    
    n = some multiple of m such that n*m is less than or equal to n2
    
    r = a remainder term to fill in the amount missing from n*m in decomposing n2
    
    x[n1] = the element in the [n1]th slot of the input string
    
    x[n1 + 1] = the element in the [n1 + 1]th slot of the input string

In general we start with a string of numbers, say 0, 1, 1, 2, 3, 3 and end up with a string of (k+1)m-1 terms, where k is the number of terms you started with. To use the function we first fix an m, say m = 2.  Now we decompose n2 in terms of m, where n2 is representing a 'slot' of our output sequence. Say n2=5.  Then we are asking 'what is in the fifth 'slot' of our output string'.  In this case our total output string will be of length (5+1)2+1.  Notice that we do not count 0 - it is always present and is for our purposes the 0th term, hence we have 5 initial terms. To answer our question of what goes in the slot we take 5=2*2+1 as our decomposition.  Now that we have a decomposition we can apply our function: 

    F(x(5)) = F(x(2*2+1)) 2x[2] + 1(x[3] - x[2]). 

The thing is, for Python to do this it has to know how to decompose each number. So it knows 2 is fixed, and knows 2*3 is too much and so chooses 2*2. Then it has to know this is too little and add remainder 1. Only once it's done this can it actually grab n = 5. That is, it can run the function. It seems clear that once it knows how to do this it can just run through every n in our range, but I'm really not sure how to program the meat of this function.

Now to answer some questions:  Is x a function? A list? A number? x[n] is essentially a list.   

What do you mean when you say "values of an input string"? What's the signature of Phi_m? 

The function acting on this list takes in a single element of the list, gives us a decomposition of the number somehow, and then applies the 'formula' you see above.  In this sense it is more of a two step algorithm.

To give another example, say we want to apply psi_2 to 0,1,2,2.  Then we have an output of length (3+1)2-1=7.  F(7)=F(2*3+1) = 2x[3] + 1(x[4] - x[3]).  As we can see, we are missing x[4] (remember 0 doesn't count as a term).  So we actually need to stop our calculation one shy of the 7 terms we 'should' have.  Hence, although we actually want 7 terms the program really only needs to give 6 terms, the other term can be hand calculated, or the user can append one extra term to the input string 0,1,2,2 and run the program again.

Please let me know if this is unclear.  I will certainly continue revising until it makes sense to those reading.

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#50849

On 18 July 2013 00:58, CTSB01 <scott.moore270@gmail.com> wrote:
> Please let me know if this is unclear.  I will certainly continue revising until it makes sense to those reading.

Can you summarize what your question is? Leave aside the details of
the function, just explain what thing in particular you aren't able
to do.

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#50869

On Thursday, July 18, 2013 5:12:08 AM UTC-4, Joshua Landau wrote:
> On 18 July 2013 00:58, CTSB01 <scott.moore270@gmail.com> wrote:
> 
> > Please let me know if this is unclear.  I will certainly continue revising until it makes sense to those reading.
> 
> 
> 
> Can you summarize what your question is? Leave aside the details of
> 
> the function, just explain what thing in particular you aren't able
> 
> to do.

Hi Joshua,

I actually managed to find a certain block like this:

 def phi_m(x, m):
...   rtn = []
...   for n2 in range(0, len(x) * m - 2:
...     n = n2 / m
...     r = n2 - n * m
...     rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
...     print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn
...   rtn 

However, I am getting the error "expected an indented block" on line two.  Any idea why?  

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#50870

On 07/18/2013 02:57 PM, CTSB01 wrote:
> On Thursday, July 18, 2013 5:12:08 AM UTC-4, Joshua Landau wrote:
>> On 18 July 2013 00:58, CTSB01 <scott.moore270@gmail.com> wrote:
>>
>>> Please let me know if this is unclear.  I will certainly continue revising until it makes sense to those reading.
>>
>>
>> Can you summarize what your question is? Leave aside the details of
>>
>> the function, just explain what thing in particular you aren't able
>>
>> to do.
> Hi Joshua,
>
> I actually managed to find a certain block like this:
>
>   def phi_m(x, m):
> ...   rtn = []
> ...   for n2 in range(0, len(x) * m - 2:
That 'for' line has miss-matched parentheses.
> ...     n = n2 / m
> ...     r = n2 - n * m
> ...     rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
> ...     print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn
> ...   rtn
>
> However, I am getting the error "expected an indented block" on line two.  Any idea why?


-- 
Dr. Gary Herron
Department of Computer Science
DigiPen Institute of Technology
(425) 895-4418

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#50871

On Thursday, July 18, 2013 6:12:52 PM UTC-4, Gary Herron wrote:
> On 07/18/2013 02:57 PM, CTSB01 wrote:
> 
> > On Thursday, July 18, 2013 5:12:08 AM UTC-4, Joshua Landau wrote:
> 
> >> On 18 July 2013 00:58, CTSB01 <scott.moore270@gmail.com> wrote:
> 
> >>
> 
> >>> Please let me know if this is unclear.  I will certainly continue revising until it makes sense to those reading.
> 
> >>
> 
> >>
> 
> >> Can you summarize what your question is? Leave aside the details of
> 
> >>
> 
> >> the function, just explain what thing in particular you aren't able
> 
> >>
> 
> >> to do.
> 
> > Hi Joshua,
> 
> >
> 
> > I actually managed to find a certain block like this:
> 
> >
> 
> >   def phi_m(x, m):
> 
> > ...   rtn = []
> 
> > ...   for n2 in range(0, len(x) * m - 2:
> 
> That 'for' line has miss-matched parentheses.
> 
> > ...     n = n2 / m
> 
> > ...     r = n2 - n * m
> 
> > ...     rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
> 
> > ...     print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn
> 
> > ...   rtn
> 
> >
> 
> > However, I am getting the error "expected an indented block" on line two.  Any idea why?
> 
> 
> 
> 
> 
> -- 
> 
> Dr. Gary Herron
> 
> Department of Computer Science
> 
> DigiPen Institute of Technology
> 
> (425) 895-4418

Hi Gary,

I fixed that issue, but I still end up with the same error.  Specifically:

		      
  File "<pyshell#9>", line 2
    ...   rtn = []
    ^
IndentationError: expected an indented block

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#50874

[Multipart message — attachments visible in raw view] — view raw

On Jul 18, 2013 4:23 PM, "CTSB01" <scott.moore270@gmail.com> wrote:
>
>   File "<pyshell#9>", line 2
>     ...   rtn = []
>     ^

The "..." is the continuation prompt from the interactive interpreter, not
part of the code. Don't paste it into Python.

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#50875

On Thursday, July 18, 2013 6:49:03 PM UTC-4, Ian wrote:
> On Jul 18, 2013 4:23 PM, "CTSB01" <scott.m...@gmail.com> wrote:
> 
> >
> 
> >   File "<pyshell#9>", line 2
> 
> >     ...   rtn = []
> 
> >     ^
> 
> The "..." is the continuation prompt from the interactive interpreter, not part of the code. Don't paste it into Python.

Thanks Ian.  That worked regarding that issue.  Now I have an 'invalid syntax' issue unfortunately.

>> def phi_m(x,m):
      rtn = []
      for n2 in range(0, len(x)*m - 2):
        n = n2 / m
        r = n2 - n * m
        rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
        print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn
      rtn

on the line  print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn  Is it something obvious?

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#50876

On Thu, Jul 18, 2013 at 5:04 PM, CTSB01 <scott.moore270@gmail.com> wrote:
> Thanks Ian.  That worked regarding that issue.  Now I have an 'invalid syntax' issue unfortunately.
>
>>> def phi_m(x,m):
>       rtn = []
>       for n2 in range(0, len(x)*m - 2):
>         n = n2 / m
>         r = n2 - n * m
>         rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
>         print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn
>       rtn
>
> on the line  print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn  Is it something obvious?

Are you using Python 2 or 3?  "print" has changed from a statement to
a function, so the above syntax would be invalid in Python 3.

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#50877

On Thu, Jul 18, 2013 at 5:42 PM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> On Thu, Jul 18, 2013 at 5:04 PM, CTSB01 <scott.moore270@gmail.com> wrote:
>> Thanks Ian.  That worked regarding that issue.  Now I have an 'invalid syntax' issue unfortunately.
>>
>>>> def phi_m(x,m):
>>       rtn = []
>>       for n2 in range(0, len(x)*m - 2):
>>         n = n2 / m
>>         r = n2 - n * m
>>         rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
>>         print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn
>>       rtn
>>
>> on the line  print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn  Is it something obvious?
>
> Are you using Python 2 or 3?  "print" has changed from a statement to
> a function, so the above syntax would be invalid in Python 3.

Note also that in Python 3 you should change the line "n = n2 / m" to
"n = n2 // m" because the syntax for integer division has also
changed.

And regardless of your Python version, the last line should probably
be "return rtn", not just "rtn".

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#50880

On Thursday, July 18, 2013 7:45:49 PM UTC-4, Ian wrote:
> On Thu, Jul 18, 2013 at 5:42 PM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> 
> > On Thu, Jul 18, 2013 at 5:04 PM, CTSB01 <scott.moore270@gmail.com> wrote:
> 
> >> Thanks Ian.  That worked regarding that issue.  Now I have an 'invalid syntax' issue unfortunately.
> 
> >>
> 
> >>>> def phi_m(x,m):
> 
> >>       rtn = []
> 
> >>       for n2 in range(0, len(x)*m - 2):
> 
> >>         n = n2 / m
> 
> >>         r = n2 - n * m
> 
> >>         rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
> 
> >>         print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn
> 
> >>       rtn
> 
> >>
> 
> >> on the line  print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn  Is it something obvious?
> 
> >
> 
> > Are you using Python 2 or 3?  "print" has changed from a statement to
> 
> > a function, so the above syntax would be invalid in Python 3.
> 
> 
> 
> Note also that in Python 3 you should change the line "n = n2 / m" to
> 
> "n = n2 // m" because the syntax for integer division has also
> 
> changed.
> 
> 
> 
> And regardless of your Python version, the last line should probably
> 
> be "return rtn", not just "rtn".

Thanks!  I'm using 3.3.2.  As I'm new to this, do you think it's a better idea to jump to 3.3.2 or stick with 2.7?  I, for all intents and purposes, know neither.

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#50878

On Fri, 19 Jul 2013 00:04:33 +0100, CTSB01 <scott.moore270@gmail.com>  
wrote:

> On Thursday, July 18, 2013 6:49:03 PM UTC-4, Ian wrote:
>> On Jul 18, 2013 4:23 PM, "CTSB01" <scott.m...@gmail.com> wrote:
>>
>> >
>>
>> >   File "<pyshell#9>", line 2
>>
>> >     ...   rtn = []
>>
>> >     ^
>>
>> The "..." is the continuation prompt from the interactive interpreter,  
>> not part of the code. Don't paste it into Python.
>
> Thanks Ian.  That worked regarding that issue.  Now I have an 'invalid  
> syntax' issue unfortunately.
>
>>> def phi_m(x,m):
>       rtn = []
>       for n2 in range(0, len(x)*m - 2):
>         n = n2 / m
>         r = n2 - n * m
>         rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
>         print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn
>       rtn
>
> on the line  print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn  Is  
> it something obvious?

Are you using Python 2.x or 3.x?  That print statement is valid 2.x, but  
"print" is a function in Python 3, so the parameter need parentheses  
around them.

This would all involve a lot less guesswork if you cut and pasted both  
your code and the error traceback.

-- 
Rhodri James *-* Wildebeest Herder to the Masses

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#50879

On 07/18/2013 07:04 PM, CTSB01 wrote:
> On Thursday, July 18, 2013 6:49:03 PM UTC-4, Ian wrote:
>> On Jul 18, 2013 4:23 PM, "CTSB01" <scott.m...@gmail.com> wrote:
>>
>>>
>>
>>>    File "<pyshell#9>", line 2
>>
>>>      ...   rtn = []
>>
>>>      ^
>>
>> The "..." is the continuation prompt from the interactive interpreter, not part of the code. Don't paste it into Python.
>
> Thanks Ian.  That worked regarding that issue.  Now I have an 'invalid syntax' issue unfortunately.
>
>>> def phi_m(x,m):
>        rtn = []
>        for n2 in range(0, len(x)*m - 2):
>          n = n2 / m
>          r = n2 - n * m
>          rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
>          print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn
>        rtn
>
> on the line  print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn  Is it something obvious?
>

It's only obvious if you're using Python 3.x.  You have forgotten the 
parentheses in the call to the print() function.

On the other hand, if this is Python 2.x, I have no idea.  Next time, 
please paste the actual error, not paraphrased.  The error message 
includes a traceback. and a pointer to where in the line the error was 
detected.  If it's pointing at the end of the second token, you must be 
running Python 3.x

And since you're using that annoying googlegroups, see this:

http://wiki.python.org/moin/GoogleGroupsPython




-- 
DaveA

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#50881

 > It's only obvious if you're using Python 3.x.  You have forgotten the 
> 
> parentheses in the call to the print() function.
> 
> 
> On the other hand, if this is Python 2.x, I have no idea.  Next time, 
> 
> please paste the actual error, not paraphrased.  The error message 
> 
> includes a traceback. and a pointer to where in the line the error was 
> 
> detected.  If it's pointing at the end of the second token, you must be 
> 
> running Python 3.x
> And since you're using that annoying googlegroups, see this:
>
> http://wiki.python.org/moin/GoogleGroupsPython
> 
> 
> -- 
> 
> DaveA

Hi Dave,

There aren't any emails in the Cc slot so I imagine that part is fine, I will definitely edit the extra quotes though I made the mistake of thinking it was just google being google.  For reference , I'm running Python 3.x.  I'll try out putting the quotes around it.   The full code is:

>>> def phi_m(x,m):
      rtn = []
      for n2 in range(0, len(x)*m - 2):
        n = n2 / m
        r = n2 - n * m
        rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
        print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn
      rtn
      
SyntaxError: invalid syntax

where the second apostrophe in 'n2 =' is marked in orange.  Thanks to everyone who's helped out so far, hopefully with some experience I'll be able sort out any syntax issues that come my way.

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#50883

On 07/18/2013 08:35 PM, CTSB01 wrote:
>   > It's only obvious if you're using Python 3.x.  You have forgotten the
>>
>> parentheses in the call to the print() function.
>>
>>
>> On the other hand, if this is Python 2.x, I have no idea.  Next time,
>>
>> please paste the actual error, not paraphrased.  The error message
>>
>> includes a traceback. and a pointer to where in the line the error was
>>
>> detected.  If it's pointing at the end of the second token, you must be
>>
>> running Python 3.x
>> And since you're using that annoying googlegroups, see this:
>>
>> http://wiki.python.org/moin/GoogleGroupsPython
>>
>>
>> --
>>
>> DaveA
>
> Hi Dave,
>
> There aren't any emails in the Cc slot so I imagine that part is fine, I will definitely edit the extra quotes though I made the mistake of thinking it was just google being google.

Exactly.  And remember, the list is comp.lang.python, while googlegroups 
has tried to pre-empt it by bridging.  Most of us get to it either 
through the nntp server at gmane.org or via email subscription at 
python-list-request@python.org


>  For reference , I'm running Python 3.x.
 >  I'll try out putting the quotes around it.

Parentheses, not quotes.  print() is a function in 3.x

>   The full code is:
>
>>>> def phi_m(x,m):
>        rtn = []
>        for n2 in range(0, len(x)*m - 2):
>          n = n2 / m
>          r = n2 - n * m
>          rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
>          print 'n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn
>        rtn
>
> SyntaxError: invalid syntax
>
> where the second apostrophe in 'n2 =' is marked in orange.  Thanks to everyone who's helped out so far, hopefully with some experience I'll be able sort out any syntax issues that come my way.
>
Don't paraphrase.  Just copy/paste it into your email message.  And I'm 
assuming you know to run things from the terminal window, and not from 
IDLE or something else that messes up the error messages.  Your comment 
about 'orange' doesn't sound promising.

As Ian pointed out, you have no return value in this function.  You 
calculate something called 'rtn', but never use it.  The last line 
accomplishes nothing, since rtn is neither assigned nor returned, nor 
passed nor...   You probably wanted:

       return  rtn





-- 
DaveA

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#50884

Thanks for the alternative links, I'll use gmane.org as an access point next time.

> 
> Don't paraphrase.  Just copy/paste it into your email message.  And I'm 
> 
> assuming you know to run things from the terminal window, and not from 
> 
> IDLE or something else that messes up the error messages.  Your comment 
> 
> about 'orange' doesn't sound promising.
> 
> 
> 
> As Ian pointed out, you have no return value in this function.  You 
> 
> calculate something called 'rtn', but never use it.  The last line 
> 
> accomplishes nothing, since rtn is neither assigned nor returned, nor 
> 
> passed nor...   You probably wanted:
> 
> 
> 
>        return  rtn
>

Does something like 

def phi_m(x, m):
          rtn = []
          for n2 in range(0, len(x) * m - 2):
            n = n2 / m
            r = n2 - n * m
            rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
            print ('n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn)
          return rtn

look right?

It doesn't seem to have any errors.  However, I do receive the following error when trying to implement an x after having defined phi:

>>> x = [0, 1, 1, 2, 3]
>>> phi_m(x, 2)
Traceback (most recent call last):
  File "<pyshell#6>", line 1, in <module>
    phi_m(x, 2)
  File "<pyshell#2>", line 6, in phi_m
    rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
TypeError: list indices must be integers, not float

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#50885

On 07/18/2013 10:16 PM, CTSB01 wrote:
>
>>
>
> Does something like
>
> def phi_m(x, m):
>            rtn = []
>            for n2 in range(0, len(x) * m - 2):
>              n = n2 / m
>              r = n2 - n * m
>              rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
>              print ('n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn)
>            return rtn
>
> look right?

No, as Ian has pointed out, you need to use the // operator in Python 3 
if you want to get integer results.  So it'd be n = n2 // m

However, even better is to use the divmod() function, which  is intended 
for the purpose:

     n, r = divmod(n2, m)

>
> It doesn't seem to have any errors.  However, I do receive the following error when trying to implement an x after having defined phi:
>
>>>> x = [0, 1, 1, 2, 3]
>>>> phi_m(x, 2)
> Traceback (most recent call last):
>    File "<pyshell#6>", line 1, in <module>
>      phi_m(x, 2)
>    File "<pyshell#2>", line 6, in phi_m
>      rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
> TypeError: list indices must be integers, not float
>

That will be fixed if you correct the code as I described, so you'll get 
integers.

There is a Brezenham algorith that might accomplish this whole function 
more accurately, or more efficiently.  But I'd have to re-derive it, as 
it's been about 30 years since I used it.  And chances are that the 
efficiencies it brought to machine code won't matter much here.




-- 
DaveA

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#50888

On Thursday, July 18, 2013 10:43:11 PM UTC-4, Dave Angel wrote:
> On 07/18/2013 10:16 PM, CTSB01 wrote:

> > Does something like
> 
> >
> 
> > def phi_m(x, m):
> 
> >            rtn = []
> 
> >            for n2 in range(0, len(x) * m - 2):
> 
> >              n = n2 / m
> 
> >              r = n2 - n * m
> 
> >              rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
> 
> >              print ('n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn)
> 
> >            return rtn
> > look right?
> 
> No, as Ian has pointed out, you need to use the // operator in Python 3 
> 
> if you want to get integer results.  So it'd be n = n2 // m
> 
> However, even better is to use the divmod() function, which  is intended 
> 
> for the purpose:
> 
> 
> 
>      n, r = divmod(n2, m)
> 
> > It doesn't seem to have any errors.  However, I do receive the following error when trying to implement an x after having defined phi:
> 
> >>>> x = [0, 1, 1, 2, 3]
> 
> >>>> phi_m(x, 2)
> 
> > Traceback (most recent call last):
> 
> >    File "<pyshell#6>", line 1, in <module>
> 
> >      phi_m(x, 2)
> 
> >    File "<pyshell#2>", line 6, in phi_m
> 
> >      rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
> 
> > TypeError: list indices must be integers, not float
> 
> 
> That will be fixed if you correct the code as I described, so you'll get 
> 
> integers.
> 
> There is a Brezenham algorith that might accomplish this whole function 
> 
> more accurately, or more efficiently.  But I'd have to re-derive it, as 
> 
> it's been about 30 years since I used it.  And chances are that the 
> 
> efficiencies it brought to machine code won't matter much here.
> 
> -- 
> 
> DaveA

Thanks Dave, I'll take a look at that.

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#50886

[Multipart message — attachments visible in raw view] — view raw

On 19 Jul 2013 03:24, "CTSB01" <scott.moore270@gmail.com> wrote:
>
> Thanks for the alternative links, I'll use gmane.org as an access point
next time.
>
> >
> > Don't paraphrase.  Just copy/paste it into your email message.  And I'm
> >
> > assuming you know to run things from the terminal window, and not from
> >
> > IDLE or something else that messes up the error messages.  Your comment
> >
> > about 'orange' doesn't sound promising.
> >
> >
> >
> > As Ian pointed out, you have no return value in this function.  You
> >
> > calculate something called 'rtn', but never use it.  The last line
> >
> > accomplishes nothing, since rtn is neither assigned nor returned, nor
> >
> > passed nor...   You probably wanted:
> >
> >
> >
> >        return  rtn
> >
>
> Does something like
>
> def phi_m(x, m):
>           rtn = []
>           for n2 in range(0, len(x) * m - 2):
>             n = n2 / m
>             r = n2 - n * m
>             rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
>             print ('n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn)
>           return rtn
>
> look right?
>
> It doesn't seem to have any errors.  However, I do receive the following
error when trying to implement an x after having defined phi:
>
> >>> x = [0, 1, 1, 2, 3]
> >>> phi_m(x, 2)
> Traceback (most recent call last):
>   File "<pyshell#6>", line 1, in <module>
>     phi_m(x, 2)
>   File "<pyshell#2>", line 6, in phi_m
>     rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
> TypeError: list indices must be integers, not float

When you think about it, it makes sense. If you have a list, say,

[2, 5, 1]

You can say, I want the first item (0) or the third item(2) but never, the
one-and-a-halfeth (0.5) item. Python only accepts integer values when
accessing list items.

To access list items, convert your index into an integer value.

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#50887

On Thursday, July 18, 2013 10:48:23 PM UTC-4, Fábio Santos wrote:
> On 19 Jul 2013 03:24, "CTSB01" <scott.m...@gmail.com> wrote:
> 
> >
> 
> > Thanks for the alternative links, I'll use gmane.org as an access point next time.
> 
> >
> 
> > >
> 
> > > Don't paraphrase.  Just copy/paste it into your email message.  And I'm
> 
> > >
> 
> > > assuming you know to run things from the terminal window, and not from
> 
> > >
> 
> > > IDLE or something else that messes up the error messages.  Your comment
> 
> > >
> 
> > > about 'orange' doesn't sound promising.
> 
> > >
> 
> > >
> 
> > >
> 
> > > As Ian pointed out, you have no return value in this function.  You
> 
> > >
> 
> > > calculate something called 'rtn', but never use it.  The last line
> 
> > >
> 
> > > accomplishes nothing, since rtn is neither assigned nor returned, nor
> 
> > >
> 
> > > passed nor...   You probably wanted:
> 
> > >
> 
> > >
> 
> > >
> 
> > >        return  rtn
> 
> > >
> 
> >
> 
> > Does something like
> 
> >
> 
> > def phi_m(x, m):
> 
> >           rtn = []
> 
> >           for n2 in range(0, len(x) * m - 2):
> 
> >             n = n2 / m
> 
> >             r = n2 - n * m
> 
> >             rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
> 
> >             print ('n2 =', n2, ': n =', n, ' r =' , r, ' rtn =', rtn)
> 
> >           return rtn
> 
> >
> 
> > look right?
> 
> >
> 
> > It doesn't seem to have any errors.  However, I do receive the following error when trying to implement an x after having defined phi:
> 
> >
> 
> > >>> x = [0, 1, 1, 2, 3]
> 
> > >>> phi_m(x, 2)
> 
> > Traceback (most recent call last):
> 
> >   File "<pyshell#6>", line 1, in <module>
> 
> >     phi_m(x, 2)
> 
> >   File "<pyshell#2>", line 6, in phi_m
> 
> >     rtn.append(m * x[n] + r * (x[n + 1] - x[n]))
> 
> > TypeError: list indices must be integers, not float
> 
> When you think about it, it makes sense. If you have a list, say,
> 
> [2, 5, 1]
> 
> You can say, I want the first item (0) or the third item(2) but never, the one-and-a-halfeth (0.5) item. Python only accepts integer values when accessing list items.
> 
> To access list items, convert your index into an integer value.

Thanks Fabio.  Is there a statement that lets me specify that I only need it to take the integer values?

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