'Lagrange Multipliers /w sympy
I am currently trying to find the maximum radius of a circle I can manifest between existing circles around it.
i.e. I'm trying to find not only the maximum radius, but the center point most suited for it over a specific given straight line.
In order to find said maxima I'm trying to implement a generalized Lagrange multipliers solution using sympy.
If "n" represents the amount of constraints I have, then I was able to:
- Create n symbols generator.
- Perform the necessary nth-gradient over the Lagrange function
- Manifest the required inequalities (from constraints) to achieve the list of equalities and inequalities needed to be solved.
The code:
from sympy import S
from sympy import *
import sympy as smp
#Lagrange Multipliers
def sympy_distfun(cx,cy,radius):
x,y=smp.symbols('x y',real=True)
return sqrt((x-cx)**2+(y-cy)**2)-radius
def sympy_circlefun(cx,cy,radius):
x,y=smp.symbols('x y',real=True)
return (x-cx)**2+(y-cy)**2-radius**2
def sympy_linefun(slope,b):
x,y=smp.symbols('x y',real=True)
return slope*x+b-y
def lagrange_multiplier(objective,constraints):
x,y=smp.symbols('x y',real=True)
a=list(smp.symbols('a0:%d'%len(constraints),real=True))
cons=[constraints[i]*a[i] for i in range(len(a))]
L=objective+(-1)*sum(cons)
gradL=[smp.diff(L,var) for var in [x,y]+a]
constraints=[(con)>= 0 for con in constraints]
eqs=gradL+constraints
vars=a+[x,y]
solution=smp.solve(eqs[0],vars)
#solution=smp.solveset(eqs,vars)
print(solution)
line=sympy_linefun(0.66666,-4.3333)
dist=sympy_distfun(11,3,4)
circlefunc1=sympy_circlefun(11,3,4)
circlefunc2=sympy_circlefun(0,0,3)
lagrange_multiplier(dist,[line,circlefunc1,circlefunc2])
But, when using smp.solveset(eqs,vars) I encounter the error message:
ValueError: [-0.66666*a0 - a1*(2*x - 22) - 2*a2*x + (x - 11)/sqrt((x - 11)**2 + (y - 3)**2), a0 - a1*(2*y - 6) - 2*a2*y + (y - 3)/sqrt((x - 11)**2 + (y - 3)**2), -0.66666*x + y + 4.3333, -(x - 11)**2 - (y - 3)**2 + 16, -x**2 - y**2 + 9, 0.66666*x - y - 4.3333 >= 0, (x - 11)**2 + (y - 3)**2 - 16 >= 0, x**2 + y**2 - 9 >= 0] is not a valid SymPy expression
When using: solution=smp.solve(eqs[0],vars) to try and solve one equation, it sends sympy into a CPU crushing frenzy and it obviously fails to complete the calculation. I made sure to declare all variables as real so i fail to see why it takes so long to solve.
Would like to understand what I'm missing when it comes to handling multiple inequalities with sympy, and if there is a more optimized faster way to solve Lagrange multiplication I'd love to give it a try
Sources
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