rounding error

[boomusters]

hey i have a rounding error somewhere in there, im supposed to get a list of numbers and output the derivitive, can someone tell me my error?

Python:

final = [0.0]     term = 0.0     for i in range (len(poly)):         term = [(poly[i]*(i)),2]         if i >=1:              final.append(term)     return final

Mod Edit:

Pleas wrap you code in either of the following in order to preserve whitespace and to highlight the syntax.

code:

[syntax="python"] ... code ... [/syntax] [code] ... code ... [/code ]

[Insectoid]

There will always be risk of rounding errors whenever you use real numbers. I suggest you use integers for everything and only convert to real after all calculations have been done (ideally during/just prior to output).

[boomusters]

Insectoid @ Sat Oct 20, 2012 5:50 pm wrote:

There will always be risk of rounding errors whenever you use real numbers. I suggest you use integers for everything and only convert to real after all calculations have been done (ideally during/just prior to output).

i would prefer to but i need exact answers for the calculations, for example if it rounded to 14.002 and the answer was 14.000099 my answer would be wrong

[Ultrahex]

you either need to use a numerically stable solution; the easiest solution is to not use floating point numbers.

If the given input is a list of integers, then you can get away without ever using floating point in this solution.

[QuantumPhysics]

Yea, I can tell you your error. First of all, where is poly declared? -> possible source of error

Second of all, you must make final an open ended list if you plan to add multiple values into it. Just like an array leave the [ ] space blank so you can add an in definitive+ amount of values into it. Not 0.0

[boomusters]

QuantumPhysics @ Sun Oct 21, 2012 3:33 pm wrote:

Yea, I can tell you your error. First of all, where is poly declared? -> possible source of error

Second of all, you must make final an open ended list if you plan to add multiple values into it. Just like an array leave the [ ] space blank so you can add an in definitive+ amount of values into it. Not 0.0

poly is the temperary variable in a function def derivities(poly)
it works but if only 1 number is inputed like "[7]" i need it to output 0.0 and it outputs []

[QuantumPhysics]

Please post your whole code and I'll make sure to help you out 101%

[boomusters]

QuantumPhysics @ Sun Oct 21, 2012 6:30 pm wrote:

Please post your whole code and I'll make sure to help you out 101%

def computeDeriv(poly):
final = []
term = 0.0
for i in range (len(poly)):
term = (poly[i]*(i))
if i >=1:
final.append(term)
return final

[QuantumPhysics]

So you want it to round final to decimal notation?

[boomusters]

QuantumPhysics @ Sun Oct 21, 2012 6:35 pm wrote:

So you want it to round final to decimal notation?

correct! and thanks for helping!

[QuantumPhysics]

To convert a value to decimal places you can type return '%.3f' % x

% is the iterator
.3f = 3 decimal places change to any value for number of decimal places
% = value sign
x = value you want to convert to 3 decimal places

you can also do:

# external library
from decimal import *
# 2 = number of decimal places
getcontext(variable).prec = 2
return variable

Either than that I hardly know of any ways to convert to decimal places with python.
I cannot test this for you, sorry. I am not in my python environment atm

[boomusters]

QuantumPhysics @ Sun Oct 21, 2012 7:14 pm wrote:

To convert a value to decimal places you can type return '%.3f' % x

% is the iterator
.3f = 3 decimal places change to any value for number of decimal places
% = value sign
x = value you want to convert to 3 decimal places

you can also do:

# external library
from decimal import *
# 2 = number of decimal places
getcontext(variable).prec = 2
return variable

Either than that I hardly know of any ways to convert to decimal places with python.
I cannot test this for you, sorry. I am not in my python environment atm

ok well thank you anyway!

[QuantumPhysics]

Your welcome, really sorry I couldn't help ya anymore.