plus/minus operator for python ±
Question:
I am looking for a way to do a plus/minus operation in python 2 or 3. I do not know the command or operator, and I cannot find a command or operator to do this.
Am I missing something?
Answers:
I think you want that for an equation like this;
Well there is no operator for that unless you don’t use SymPy, only you can do is make an if statement and find each multiplier.
Another possibility: uncertainties is a module for doing calculations with error tolerances, ie
(2.1 +/- 0.05) + (0.6 +/- 0.05) # => (2.7 +/- 0.1)
which would be written as
from uncertainties import ufloat
ufloat(2.1, 0.05) + ufloat(0.6, 0.05)
Edit: I was getting some odd results, and after a bit more playing with this I figured out why: the specified error is not a tolerance (hard additive limits as in engineering blueprints) but a standard-deviation value – which is why the above calculation results in
ufloat(2.7, 0.07071) # not 0.1 as I expected!
There is no such object in SymPy yet (as you saw, there is an issue suggesting one https://github.com/sympy/sympy/issues/5305). It’s not hard to emulate, though. Just create a Symbol, and swap it out with +1 and -1 separately at the end. Like
pm = Symbol(u'±') # The u is not needed in Python 3. I used ± just for pretty printing purposes. It has no special meaning.
expr = 1 + pm*x # Or whatever
# Do some stuff
exprpos = expr.subs(pm, 1)
exprneg = expr.subs(pm, -1)
You could also just keep track of two equations from the start.
If you happen to be using matplotlib, you can print mathematical expressions similar as one would with Latex. For the +/- symbol, you would use:
print( r"value $pm$ error" )
Where the r converts the string to a raw format and the $-signs are around the part of the string that is a mathematical equation. Any words that are in this part will be in a different font and will have no whitespace between them unless explicitly noted with the correct code. This can be found on the relavent page of the matplotlib documentation.
Sorry if this is too niche, but I stumbeled across this question trying to find this very answer.
Instead of computing expressions like
s1 = sqrt((125 + 10 * sqrt(19)) / 366)
s2 = sqrt((125 - 10 * sqrt(19)) / 366)
you could use
import numpy as np
pm = np.array([+1, -1])
s1, s2 = sqrt((125 + pm * 10 * sqrt(19)) / 366)
If you are looking to print the ± symbol, just use:
print(u"u00B1")
A plus/minus tolerance test can be done using a difference and absolute against the tolerance you wish to test for. Something like:
tst_data = Number you wish to test
norm = Target number
tolerance = Whatever the allowed tolerance is.
if abs(tst_data - norm) <= tolerance:
do stuff
Using the abs function allows the test to return a +/- within tolerance as True
I am looking for a way to do a plus/minus operation in python 2 or 3. I do not know the command or operator, and I cannot find a command or operator to do this.
Am I missing something?
I think you want that for an equation like this;
Well there is no operator for that unless you don’t use SymPy, only you can do is make an if statement and find each multiplier.
Another possibility: uncertainties is a module for doing calculations with error tolerances, ie
(2.1 +/- 0.05) + (0.6 +/- 0.05) # => (2.7 +/- 0.1)
which would be written as
from uncertainties import ufloat
ufloat(2.1, 0.05) + ufloat(0.6, 0.05)
Edit: I was getting some odd results, and after a bit more playing with this I figured out why: the specified error is not a tolerance (hard additive limits as in engineering blueprints) but a standard-deviation value – which is why the above calculation results in
ufloat(2.7, 0.07071) # not 0.1 as I expected!
There is no such object in SymPy yet (as you saw, there is an issue suggesting one https://github.com/sympy/sympy/issues/5305). It’s not hard to emulate, though. Just create a Symbol, and swap it out with +1 and -1 separately at the end. Like
pm = Symbol(u'±') # The u is not needed in Python 3. I used ± just for pretty printing purposes. It has no special meaning.
expr = 1 + pm*x # Or whatever
# Do some stuff
exprpos = expr.subs(pm, 1)
exprneg = expr.subs(pm, -1)
You could also just keep track of two equations from the start.
If you happen to be using matplotlib, you can print mathematical expressions similar as one would with Latex. For the +/- symbol, you would use:
print( r"value $pm$ error" )
Where the r converts the string to a raw format and the $-signs are around the part of the string that is a mathematical equation. Any words that are in this part will be in a different font and will have no whitespace between them unless explicitly noted with the correct code. This can be found on the relavent page of the matplotlib documentation.
Sorry if this is too niche, but I stumbeled across this question trying to find this very answer.
Instead of computing expressions like
s1 = sqrt((125 + 10 * sqrt(19)) / 366)
s2 = sqrt((125 - 10 * sqrt(19)) / 366)
you could use
import numpy as np
pm = np.array([+1, -1])
s1, s2 = sqrt((125 + pm * 10 * sqrt(19)) / 366)
If you are looking to print the ± symbol, just use:
print(u"u00B1")
A plus/minus tolerance test can be done using a difference and absolute against the tolerance you wish to test for. Something like:
tst_data = Number you wish to test
norm = Target number
tolerance = Whatever the allowed tolerance is.
if abs(tst_data - norm) <= tolerance:
do stuff
Using the abs function allows the test to return a +/- within tolerance as True