def calculate_lagrange_polynomials(x_values):
"""
Given the x_values for evaluating some polynomials, it computes part of the lagrange polynomials
required to interpolate a polynomial over this domain.
"""
lagrange_polynomials = []
monomials = [
Polynomial.monomial(1, FieldElement.one()) - Polynomial.monomial(0, x)
for x in x_values
]
numerator = prod(monomials)
for j in tqdm(range(len(x_values))):
# In the denominator, we have:
# (x_j-x_0)(x_j-x_1)...(x_j-x_{j-1})(x_j-x_{j+1})...(x_j-x_{len(X)-1})
denominator = prod(
[x_values[j] - x for i, x in enumerate(x_values) if i != j])
# Numerator is a bit more complicated, since we need to compute a poly multiplication here.
# Similarly to the denominator, we have:
# (x-x_0)(x-x_1)...(x-x_{j-1})(x-x_{j+1})...(x-x_{len(X)-1})
cur_poly, _ = numerator.qdiv(monomials[j].scalar_mul(denominator))
lagrange_polynomials.append(cur_poly)
return lagrange_polynomials
def test_field_div():
for _ in range(100):
t = FieldElement.random_element(exclude_elements=[FieldElement.zero()])
t_inv = FieldElement.one() / t
assert t_inv == t.inverse()
assert t_inv * t == FieldElement.one()
def test_field_operations():
# Check pow, mul, and the modular operations
t = FieldElement(2).pow(30) * FieldElement(3) + FieldElement(1)
assert t == FieldElement(0)
def __init__(self, coefficients, var='x'):
# Internally storing the coefficients in self.poly, least-significant (i.e. free term)
# first, so $9 - 3x^2 + 19x^5$ is represented internally by the list [9, 0, -3, 0, 0, 19].
# Note that coefficients is copied, so the caller may freely modify the given argument.
self.poly = remove_trailing_elements(coefficients, FieldElement.zero())
self.var = var
def X(cls):
"""
Returns the polynomial x.
"""
return cls([FieldElement.zero(), FieldElement.one()])
def trim_trailing_zeros(p):
"""
Removes zeros from the end of a list.
"""
return remove_trailing_elements(p, FieldElement.zero())
def gen_linear_term(point):
"""
Generates the polynomial (x-p) for a given point p.
"""
return Polynomial([FieldElement.zero() - point, FieldElement.one()])
def monomial(degree, coefficient):
"""
Constructs the monomial coefficient * x**degree.
"""
return Polynomial([FieldElement.zero()] * degree + [coefficient])
def __sub__(self, other):
other = Polynomial.typecast(other)
return Polynomial(
two_lists_tuple_operation(self.poly, other.poly, operator.sub,
FieldElement.zero()))
def test_prod():
g = FieldElement.generator()**((FieldElement.k_modulus - 1) // 1024)
assert X**1024 - 1 == prod([(X - g**i) for i in range(1024)])
# a STARK proving mechanism
# from StarkWare101 Workshop
# in San Fransisco, 2/17/20
##########
# PART 1 #
##########
# first step is to create a list of length 1023
# first two elements are FieldElement objects
# representing 1 and 3141592 respectively.
a = [FieldElement(1), FieldElement(3141592)]
while len(a) < 1023:
a.append(a[-2] * a[-2] + a[-1] * a[-1])
# quick unit test to verify a[] constructed properly
assert len(a) == 1023, 'The trace must consist of exactly 1023 elements.'
assert a[0] == FieldElement(1), 'The first element in the trace must be the unit element.'
for i in range(2, 1023):
assert a[i] == a[i - 1] * a[i - 1] + a[i - 2] * a[i - 2], f'The FibonacciSq recursion rule does not apply for index {i}'
assert a[1022] == FieldElement(2338775057), 'Wrong last element!'
print('Success!')
# need a generator from field element class
# need to generator a group of size 1024
g = FieldElement.generator() ** (3 * 2 ** 20)
