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  • 09:19
    johannesflake opened #22133
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    asmeurer commented #21945
  • Sep 21 20:29

    smichr on master

    point2D now will subclass Evalf… fixed failing tests test evalf for entities Also, … and 1 more (compare)

  • Sep 21 20:28
    smichr closed #22131
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Ayush Bisht

@0sidharth , we can also do the same thing by passing a list of numbers to sympy.lcm( ) method.

import sympy

1 reply
Benoit Martin
Hi, there a way to pprint(simplify(e)) with explanation. Or all step to simplify ?
1 reply
Kartik Sethi
hi there, is there some way to get a matrix with kth diagonal populated as input array, like Matlab's diag(A,k)
Ayush Bisht

from sympy import *
x,y,z = symbols("x y z")
exp = (x+z)&2
TypeError: unsupported operand type(s) for &: 'Add' and 'int'

how can we implement bitwise operation with sympy.

Sayandip Halder
Currently, solve([x - 5], x) gives the dict {x: 5} as solution. However, solve([sin(x)], x) and solve([x**2-4],x) does not return a dict solution unless stated explicitly.
Shouldn't solve([x - 5], x) simply return [5]?
Benoit Martin
Normally when I divide I subtract exp but here it looks like the exp is being increased.
Benoit Martin
Benoit Martin
e25_4 = ((-4*a*b**2/-2*a**2*c**2) + (14*a**4*c/-2*a**2*c**2))
Result -7*a**6*c**3 + 2*a**3*b**2*c**2
1 reply
Ayush Bisht
can someone review my PR #20919
this one also , #20923
Aaron Meurer
@ayushbisht2001 ilcm accepts any number of arguments
2 replies

Hi everyone, can someone give me some recommendation to the next problem, I have a large expression lambdified, the problem is that has Nan results when I evaluate. I have found one term which causes this behavior and given by:

from sympy import init_printing,symbols,log,sqrt

m = symbols('m')
f = 0.5*log(1 - 3.13400648e+22/(1.56700324e+22*sqrt(1 - 1.5976993129893e-11*m)*sqrt(1.5976993129893e-11*m + 1) + 1.56700324e+22))

Then, when I substitute in $m=1e-3$


Which give $\tilde{\infty}$. However, if I use evalf command I obtain

-32.4607738174251 + 1.5707963267949*I

Then, I don't know what result is correct. Is this a problem of the precision of subs command?.

Aaron Meurer
evalf is more accurate. The problem is that when using subs, the expression inside of the log is not evaluated to enough precision to distinguish it from 0
evalf(subs=...) handles cases like this where naive substitution leads to loss of significance
for lambdify, you are going to run into this same problem, because you are evaluating it naively. You will need to rewrite the expression somehow to avoid the massive cancellation.
Generally, you'd want to evaluate something like this using log1p.
Aaron Meurer
You can use sympy.codegen.cfunctions.log1p. But I still get issues with it, so you need to make some other changes.
Maybe log1p isn't actually applicable here, since the argument is near 0, not near 1
Aaron Meurer
If you are just using SymPy, you can fix this problem by converting the floats to rationals. Then subs will be able to evaluate it more accurately. But for lambdify to numpy, you will need to figure out how to rewrite the expression to be more numerically stable.
Aaron Meurer
A suggestion would be to multiply and distribute a large value inside of the log then subtract the log of that value. That way the number evaluated in the log isn't so close to 0.
Ayush Bisht
@asmeurer , some of the test are failing in my PR's #20923 #20919, please do review.
1 reply

@asmeurer Thanks for the suggestions and the explanation. My expression is too large because I obtained after some SymPy calculations and I do not how to rewrite the log function following your suggestions of multiply for a big number inside of log. I have tried to create a new log function like log_rewrite(x) = log(x*y) - log(y) with y a big number and after using lambdify command to the f function

from numpy import log as nplog
def log_rewritted(x):
    y = 1e30
    return nplog(x*y)-nplog(y)

fnp = lambdify([m],f,modules=[{'log':log_rewritted}])

However, I obtained the same result when I evaluate f,

hey guys i am new to open source and an aspirant for gsoc 2021. i want to contribute towards sympy . can anyone guide me and help me towards what issue should be the best to start with
Aaron Meurer
@moiseszeleny I think you are going to have to rewrite what is inside of the log too. It already rounds down to 0, so simply multiplying it by a larger number won't do anything.
Ayush Bisht
hello everyone , does use_unicode is False by default in pprint( )
1 reply
Ayush Bisht
I have tried to correct something in doc .Refer : #20919
Craig Russell
Can one use the integral transforms on numeric data?


from sympy.abc import  x, k
from sympy import Sum

print(Sum(1/2**x, (x, 0, k)).evalf())

give 2.00000000000000 like it was an infinte series?

5 replies
Aaron Meurer
Looks like a bug. Can you open an issue?
@asmeurer new to the project I will try to look at the reccomanded way to write a issue ..
but if someone already familiar with process do it before ...I will learn directly from it ..
Aaron Meurer
It's not that complicated. Just go to https://github.com/sympy/sympy/issues/new and note the example that is wrong.
Ayush Bisht
#4886 I want to work on this issue , can someone suggest me how to start?? where the test file should be added . I am unable to figure out it.
Ayush Bisht
I have found some conflict with my PR #20935 , can someone help me ??
Sum(x**2, (x, 1, k)).evalf() and expression which derivative is not a constant raise TypeError
this should come from the euler_maclaurin when it compare a symbolic expression to a float...
why the code does not take in consideration the symbolic case?
Janmay Bhatt
Hi everyone, I am Janmay from Nirma University, India and I want to contribute into sympy library. I am CSE student, second year. I have done a research in mathematics related to prime numbers which is prime conjecture(here https://www.ijmttjournal.org/archive/ijmtt-v60p505).
This research have function for series of prime numbers and you can generate the any prime with a reference. I have read about the contribution in sympy so may someone please guide me about gsoc
This will make the prime generation faster and precise, which I want to contribute into sympy as well as for issue #19118 in sympy repository
Ayush Bisht

I found some unusual behaviour in randprime and I try to fix it.

from sympy import randprime
ValueError: no preceding primes

Can someone please review this PR : #20949

@ayushbisht2001 Wouldn't it make sense to go all the way to 2?
for example
print(randprime(0,2)) should also print "no primes exist in the specified range"
Ayush Bisht
@laolux:wolkendienst.dynv6.net , Now , Is it good to go ?? #20949 .
1 reply
Aaron Stiff
How would I analyze a sympy object to see whether it matches a certain structure? For instance, I want to see if an object/expression matches the structure I*im(z), where z is some complex symbol.
Aaron Meurer
You can use Wild and match
Aaron Stiff
Vishesh Mangla
class Data:
    def __init__(self, string,symbol, value):
        self.string = string
        self.symbol = sm.Symbol(symbol)
        self.value = value

    def __add__(self, other):
        return self.value + other.value if isinstance(other, Data) else other

    def __str__(self):
        return self.string
    def _repr_latex_(self):
        return display(Latex(' '.join([self.string, f'({self.symbol})' ,r'\equals', self.value] )))
TypeError                                 Traceback (most recent call last)
c:\users\dell\onedrive\desktop\courses sem8\venv\lib\site-packages\IPython\core\formatters.py in __call__(self, obj)
    343             method = get_real_method(obj, self.print_method)
    344             if method is not None:
--> 345                 return method()
    346             return None
    347         else:

<ipython-input-49-83e3f780e89d> in _repr_latex_(self)
     11         return self.string
     12     def _repr_latex_(self):
---> 13         return display(Latex(' '.join([self.string, f'({self.symbol})' ,r'\equals', self.value] )))
     14 # area_each_plate = Data("Area of each plate", 15.8*15.8*SI.cm**2)
     15 # inlet_pressure = Data("Area of each plate", 15.8*15.8*SI.cm**2)

TypeError: sequence item 3: expected str instance, Quantity found
how to get the latex out of sympy's Symbol?
neither does f'({latex(self.symbol)})' work