Solveset
when domain = S.Integers
PR #11234
Right now we may not get our solution in Integer domain but we can use concept of diophantine equations in solveset
.
When I messaged about this in giiter channel Aaron told about the diophantine
, already defined in solvers/diophantine.py.
So we can use diophantine
in solveset
to get Integer solution.diophantine
is coded pretty well and works fine.
Diophantine Equations
Let P(x, y, …) is a polynomial with integer coefficients in one or more variables. A Diophantine equation is an algebraic equation
P(x, y, z, ... ) = 0
for which integer solutions are sought.
 More about diophantine equation mathworld.wolfram
Previous work on this :
PR #10994
solveset_univariate_trig_ineq :*
PR #11257
 Problem in current branch:
In [ ]: solveset((2*cos(x)+1)/(2*cos(x)1) > 0, x, S.Reals)
Out[ ]:
(oo, pi/3) \ ImageSet(Lambda(_n, 2*_n*pi + 5*pi/3), Integers()) U ImageSet(Lambda(_n, 2*_n*pi + pi/3), Integers()) U (2*pi/3, 4*pi/3) \ ImageSet(Lambda(_n, 2*_n*pi + 5*pi/3), Integers()) U ImageSet(Lambda(_n, 2*_n*pi + pi/3), Integers())
solution expected is :
(1/3)*(3*pi*n  pi) < x < (1/3)*(3*pi*n +pi), n element in Z
I am working on this and have opened PR #11257 but it is failing some cases.
I am trying to improve it. It is inspired from previous solve_univariate_inequality
but it seems need changes for trig ineq.
Main intention is to get extended solution for Trigonometric inequality.
eg.
In [2]: solveset((2*cos(x)+1)/(2*cos(x)1) > 0, x, S.Reals)
Out[2]:
⎡⎧ π ⎫ ⎧ π ⎫⎤
⎢⎨n⋅π  ─  n ∊ ℤ⎬, ⎨n⋅π + ─  n ∊ ℤ⎬⎥
⎣⎩ 3 ⎭ ⎩ 3 ⎭⎦
n [4]: solveset(sin(x) > 1/sqrt(2), x, S.Reals)
Out[4]:
⎛⎧ π ⎫ ⎧ 3⋅π ⎫⎞
⎜⎨2⋅n⋅π + ─  n ∊ ℤ⎬, ⎨2⋅n⋅π + ───  n ∊ ℤ⎬⎟
⎝⎩ 4 ⎭ ⎩ 4 ⎭⎠
In [15]: solveset(2*cos(x) + sqrt(3) < 0, x, S.Reals)
Out[15]:
⎛⎧ 5⋅π ⎫ ⎧ 7⋅π ⎫⎞
⎜⎨2⋅n⋅π + ───  n ∊ ℤ⎬, ⎨2⋅n⋅π + ───  n ∊ ℤ⎬⎟
⎝⎩ 6 ⎭ ⎩ 6 ⎭⎠
In [16]: solveset_univariate_trig_inequality(tan(x) > 0, x)
Out[16]:
⎛ ⎧ π ⎫⎞
⎜{n⋅π  n ∊ ℤ}, ⎨n⋅π + ─  n ∊ ℤ⎬⎟
⎝ ⎩ 2 ⎭⎠
 Still need some good idea to improve the PR #11257. will continue …
Continue nonlinsolve :
PR #11111

After Amit’s review and comments, I improved the
docstring
, improved thecomplements
andintersection
if
block present insubstitution
function. 
The main thing I added is : now
substitution
method will return bothReal
andComplex
solution. That mean now it is usingsolveset_real
andsolveset_complex
. Previously it usessolveset_complex
when there isS.EmpltySet
fromsolveset_real
. 
Since both
solveset_real
andsolveset_complex
solution need similar steps. So I am using_solve_using_know_values
function a helper forsubstitution
method, wheresolver
parameter can besolveset_real
orsolveset_complex
. Another parameter isresult
which is list of dict <known_symbol: it’s value> (already solved symbol, mostly fromnonlinsolve/_solve_poly_system
).
Meanwhile

Opened an issue #11236.

PR #11239 for the issue

I found that right now
diophantine
can’t handle these types of equations :
In [ ]: diophantine((x+y)**2  x**3 + y**3)

NotImplementedError: No solver has been written for cubic_thue.
continue..
Follow @shekharrajak