I've been facing strange results in a numerical problem I've been working on and since I started to program in python recently, I would like to see if you can help me.
Basically, the program has a function that is minimized for different values in a nested loop. I'll skip the details of the function for simplicity but I checked it several times and it is working correctly. Basically, the code looks like that:
def function(mins,args):
#I'll skip those details for simplicity
return #Value
ranges = ((0+np.pi/100),(np.pi/2-np.pi/100),np.pi/100)
while Ri[0] < R:
Ri[1] = 0; Ri[n-1] = R-(sum(Ri)-Ri[n-1])
while Ri[1] < (R-Ri[0]):
res = opt.brute(function, ranges, args=[args], finish=None)
F = function(res,args)
print(f'F = {F}')
Ri[1] += dR
Ri[2] = R-(sum(Ri)-Ri[n-1])
Ri[0] += dR
So, ignoring the Ri[] meaning in the loop (which is a variable of the function), for every increment in Ri[] the program makes a minimization of mins by the scipy.optimize.brute obtaining res as the answer, then it should run the function with this answer and print the result F. The problem is that it always get the same answer, no matter what the parameters I get in the minimization (which is working fine, I checked). It's strange because if I get the values from the minimization (which is an n-sized array, being n an input) and create a new program to run the same function and just get the result of the function, it returns me the right answer.
Anyone can give me a hint why I'm getting this? If I didn't make myself clear please tell and I could provide more details about the function and variables. Thanks in advance!
Related
So, really I'm just confused, I've been learning python, and I was given an exercise to find the performance speed of a function, however after finishing the code I received an error in the time output, it was 3.215000000000856e-06, this value varies with every time I run the program though so you probably won't get the same output.(in reality it was less then a second.) I went through the video where it explained how to write how they did it and changed a how I wrote a statement, now my code is Identical, to theirs but with different variable names, I ran the program and the same problem, however they didn't experience this issue, heres the code:
import time
SetContainer = {I for I in range(1002)}
ListContainer = [I for I in range(1002)]
def Search(Value, Container):
if Value in Container:
return True
else:
return False
def Function_Speed(Func, HMT = 1, **arg):
sum = 0
for I in range(HMT):
start = time.perf_counter()
print (Func(**arg))
end = time.perf_counter()
sum = sum + (end - start)
return (sum, )
print (Function_Speed(Search, Value = 402,
Container = SetContainer))
Possible Answers?:
Could it be my hardware? My version of Python is no longer supported(The video is over a year old I'm using 3.6) or it turns out I screwed up.
(Edit:) By the way it does work when the function is printed so this example works, but without print (Func(**arg)) and instead Func(**arg) it doesn't work.
First, your capitalization of variable and function violates convention. Though not a syntax error, it makes it difficult for Python programmers to follow your code.
Second, the result you got makes sense. A single iteration of the search on a modern computer takes very little time. If your printed result was in the form 1.23456e-05, then that is a valid number so small that the default representation shifted to scientific notation.
Add a value for HMT, starting with 100000, and see what is output.
I've been working on solving Problem 31 from Project Euler. I'm almost finished, but my code is giving me what I know is the wrong answer. My dad showed the right answer, and mine is giving me something completely wrong.
coins = (1,2,5,10,20,50,100,200)
amount = 200
def ways(target, avc):
target = amount
if avc <= 1:
return 1
res = 0
while target >= 0:
res = res + ways(target, avc-1)
target = target - coins[avc]
return res
print(ways(amount, 7))
This is the answer I get.
284130
The answer is supposed to 73682.
EDIT: Thank you to everyone who answered my question. Thanks to all of you, I have figured it out!
I see several ways how you can improve the way you're working on problems:
Copy the task description into your source code. This will make you more independent from Internet resources. That allows you to work offline. Even if the page is down or disappears completely, it will enable someone else understanding what problem you're trying to solve.
Use an IDE that does proper syntax highlighting and gives you hints what might be wrong with your code. The IDE will tell you what #aronquemarr mentioned in the comments:
There's also a thing called magic numbers. Many of the numbers in your code can be explained, but why do you start with an avc of 7?. Where does that number come from? 7 does not occur in the problem description.
Use better naming, so you understand better what your code does. What does avc stand for? If you think it's available_coins, that's not correct. There are 8 different coins, not 7.
If it still does not work, reduce the problem to a simpler one. Start with the most simple one you can think of, e.g. make only 1 type of coin available and set the amount to 2 cent. There should only be 1 solution.
To make sure this simple result will never break, introduce an assertion or unit test. They will help you when you change the code to work with larger datasets. They will also change the way you write code. In your case you'll find that accessing the variable coins from an outer scope is probably not a good idea, because it will break your assertion when you switch to the next level. The change that is needed will make your methods more self-contained and robust.
Then, increase the difficulty by having 2 different coins etc.
Examples for the first assertions that I used on this problem:
# Only 1 way of making 1 with only a 1 coin of value 1
assert(find_combinations([1], 1) == 1)
# Still only 1 way of making 1 with two coins of values 1 and 2
assert(find_combinations([1,2], 1) == 1)
# Two ways of making 2 with two coins of values 1 and 2
assert(find_combinations([1,2], 2) == 2)
As soon as the result does no longer match your expectation, use the debugger and step through your code. After every line, check the values in the debugger against the values that you think they should be.
One time, the debugger will be your best friend. And you can never imagine how you did stuff without it. You just need to learn how to use it.
Firstly, read Thomas Weller's answer. They give some excellent suggestions as to how to improve your coding and problem solving.
Secondly, your code works, and gives the correct answer after the following changes:
As suggested, remove the target = amount line. You're resigning the argument of the function to global amount on each call (even on the recursive calls). Having removed that the answer comes up to 3275 - still not the right answer.
The other thing you have to remember is that Python is 0-indexed. Therefore, your simplest case condition ought to read if avc <= 0: ... (not <=1).
Having made these two changes, your code gives the correct answer. Here is your code with these changes:
coins = (1,2,5,10,20,50,100,200)
amount = 200
def ways(target, avc):
if avc <= 0:
return 1
res = 0
while target >= 0:
res = res + ways(target, avc-1)
target = target - coins[avc]
return res
print(ways(amount, 7))
Lastly, there are plenty of Project Euler answers out there. Having solved the yourself, it might be useful to have a look at what others did. For reference, I have not actually solved this Project Euler before, so I had to do that first. Here is my solution. I've added a pile of comments on top of it to explain what it does.
EDIT
I've just noticed something quite worrying: Your code (after fixes) works only if the first element of coins is 1. All the other elements can be shuffled:
# This still works ok
coins = (1,2,200,10,20,50,100,5)
# But this does not
coins = (2,1,5,10,20,50,100,200)
To ensure that this is always the case, you can just do the following:
coins = ... # <- Some not necessarily sorted tuple
coins = tuple(sorted(coins))
In principle there are a few other issues. Your solution breaks for non-unique values coins, and which don't include 1. The former you could fix with the use of sets, and the latter by modifying your if avc <= 0: case (check for the divisibility of the target by the remaining coin). Here is you piece of code with these changes implemented. I've also renamed the variables and the function to be a bit easier to read, and used coins as the argument, rather that avc pointer (which, by the way, I could not stop reading as avec):
unique = lambda x: sorted(set(x)) # Sorted unique list
def find_combinations(target, coins):
''' Find the number of ways coins can make up the target amount '''
coins = unique(coins)
if len(coins)==1: # Only one coin, therefore just check divisibility
return 1 if not target%coins[0] else 0
combinations = 0
while target >= 0:
combinations += find_combinations(target, coins[:-1])
target -= coins[-1]
return combinations
coins = [2,1,5,10,20,50,100,200] # <- Now works
amount = 200
print(find_combinations(amount, coins))
I am trying to minimize a function of 3 input variables using scipy. The function reads like so-
def myfunc(x):
x[0] = a
x[1] = b
x[2] = c
n = f(a,b,c)
return n
bound1 = (80,100)
bound2 = (10,20)
bound3 = (312,740)
guess = [a0,b0,c0]
bds = (bound1,bound2,bound3)
result = minimize(myfunc, guess,method='L-BFGS-B',bounds=bds)
The function I am trying to currently run reaches a minimum at a=100,b=10,c=740, which is at the end of the bounds.
The minimize function keeps trying to iterate past the end of bound 3 (gets to c0 value of 740.0000000149012 on its last iteration.
Is there any way to stop this from happening? i.e. stop the iteration at the actual end of my bound?
This happens due to numerical-differentiation, which itself is not only needed to infer the step-direction and size, but also to reason about termination.
In general you can't do much without being very careful in regards to whatever solver (and there are many backend-solvers) being used. The basic idea is to replace the automatic numerical-differentiation with one provided by you: this one then respects those bounds and must be careful about the solvers-internals, e.g. "how to reason about termination at this end".
Fix A:
Your problem should vanish automatically when using: Pull-request #10673, which touches your configuration: L-BFGS-B.
It seems, this PR is not part of the current release SciPy 1.4.1 (as this was 2 months before the PR).
See also #6026, where a milestone of 1.5.0 is mentioned in regards to some changes including respecting bounds in num-diff.
For above PR, you will need to install scipy from the sources, which is:
quite doable on linux (and maybe os x)
not something you should try on windows!
trust me...
See the documentation if needed.
Fix B:
Apart from that, as you are doing unconstrained-optimization (with variable-bounds) where more solver-backends are available (compared to constrained-optimization), you might try another solver, trust-constr, which has explicit support for this, see #9098.
Be careful to recognize, that you need to signal this explicitly when setting up the bounds!
I am facing challenges implementing OOP in python to enable me to call the functions whenever i want , so far i have no syntax errors which makes quite challenging for me . The first part of the code runs ehich is to accept data but the function part does not run.
I have tried different ways of calling the function by creating an instance of it.
print (list)
def tempcheck(self,newList):
temp=newList[0]
if temp==27:
print ("Bedroom has ideal temperature ")
elif temp>=28 or temp<=26:
print ("Bedroom Temperature is not ideal ,either too low or too cold. ")
print ("Please to adjust the temperature to the optimum temperature which is 27 degree Celsuis")
# now to initialize args
def __init__(self,temp,puri1,bedwashroom,newList):
self.temp=temp
self.puri1=puri1
self.bedwashroom=bedwashroom
tempcheck(newList)
# now calling the functions
newvalue=tempcheck(list)
# where list contains the values from the input function.
I expected the function to to check the specific value at the location in the list provided which is called list and also for the function to return a string based on the if statements.
i got it right ,i figured out an alternative to my bug thanks for the critique however any further addition is welcome,
the main goal was to create a function that takes input and passes it to list to be used later i guess this code is less cumbersome
the link to the full code is pasted below
So, I have a function which basically does this:
import os
import json
import requests
from openpyxl import load_workbook
def function(data):
statuslist = []
for i in range(len(data[0])):
result = performOperation(data[0][i])
if result in satisfying_results:
print("its okay")
statuslist.append("Pass")
else:
print("absolutely not okay")
statuslist.append("Fail" + result)
return statuslist
Then, I invoke the function like this (I've added error handling to check what will happen after stumbling upon the reason for me asking this question), and was actually amazed by the results, as the function returns None, and then executes:
statuslist = function(data)
print(statuslist)
try:
for i in range(len(statuslist)):
anotherFunction(i)
print("Confirmation that it is working")
except TypeError:
print("This is utterly nonsense I think")
The output of the program is then as follows:
None
This is utterly nonsense I think
its okay
its okay
its okay
absolutely not okay
its okay
There is only single return statement at the end of the function, the function is not recursive, its pretty straightforward and top-down(but parses a lot of data in the meantime).
From the output log, it appears that the function first returns None, and then is properly executed. I am puzzled, and I were unable to find any similar problems over the internet (maybe I phrase the question incorrectly).
Even if there were some inconsistency in the code, I'd still expect it to return [] instead.
After changing the initial list to statuslist = ["WTF"], the return is [].
To rule out the fact that I have modified the list in some other functions performed in the function(data), I have changed the name of the initial list several times - the results are consistently beyond my comprehension
I will be very grateful on tips in debugging the issue. Why does the function return the value first, and is executed after?
While being unable to write the code which would at the same time present what happened in my code in full spectrum, be readable, and wouldn't interfere with no security policies of the company, I have re-wrote it in a simpler form (the original code has been written while I had 3 months of programming experience), and the issue does not reproduce anymore. I guess there had be some level of nesting of functions that I have misinterpreted, and this re-written code, doing pretty much the same, correctly returns me the expected list.
Thank you everyone for your time and suggestions.
So, the answer appears to be: You do not understand your own code, make it simpler.