def _eval_eq_bounded(e, subs, error_bound, under_approx, split_dim=0):
'''do bounded interval evaluation
error_bound is the desired error bound
under_approx is an array of size 1, which is an under-approximation on the result
of the interval evaluation, and may be updated as we go
split_dim is the next dimension to split (this gets cycled)
'''
rv = _eval_eq_direct(e, subs)
variables = subs.keys()
# adjust the under approximation
if rv.b < under_approx[0].a:
under_approx[0] = interval(rv.b, under_approx[0].b)
if rv.a > under_approx[0].b:
under_approx[0] = interval(under_approx[0].a, rv.a)
if rv.a < (under_approx[0].a - error_bound) or rv.b > (under_approx[0].b + error_bound):
# split along split_dim
var = variables[split_dim]
i = subs[var]
next_split_dim = (split_dim + 1) % len(subs)
bound_left = copy.deepcopy(subs)
bound_left[var] = (i[0], (i[0] + i[1]) / 2.0)
bound_right = copy.deepcopy(subs)
bound_right[var] = ((i[0] + i[1])/2.0, i[1])
rv_left = _eval_eq_bounded(e, bound_left, error_bound, under_approx, next_split_dim)
rv_right = _eval_eq_bounded(e, bound_right, error_bound, under_approx, next_split_dim)
rv = interval(min(rv_left.a, rv_right.a), max(rv_left.b, rv_right.b))
return rv
def _eval_at_corners(e, subs):
'''evaluate an expression in the middle of an interval range'''
rv = None
max_iterator = 1
for _ in xrange(len(subs)):
max_iterator *= 2
for i in xrange(max_iterator):
new_subs = {}
for var, item in subs.items():
new_subs[var] = item[i % 2]
i /= 2
val = _eval_eq_direct(e, new_subs)
if rv is None:
rv = val
if val.a < rv.a:
rv = interval(val.a, rv.b)
if val.b > rv.b:
rv = interval(rv.a, val.b)
return rv
def _test():
'''runs module unit tests'''
# Test below - tries every supported subexpression - takes a few seconds
x = symbols('x')
eq = sin(x + 0.01)
#eq = 1*x*x + (0.2-x) / x + sin(x+0.01) + sqrt(x + 1) + cos(x + 0.01) + tan(x + 0.01) - (x+0.1)**(x+0.1)
print eval_eq(eq, {'x':interval(0.20, 0.21)})
########################################################################
# Test below - makes sure evalEqMulti works as expected
x = symbols('x')
eq = x + interval(0.1)
range1 = {'x':interval(0, 1)}
range2 = {'x':interval(1, 2)}
for i in eval_eq_multi(eq, [range1, range2]):
print i
########################################################################
# Test below - makes sure eval_eq_multi_branch_bound works as expected
x = symbols('x')
eq = x*x - 2*x
range1 = {'x':interval(0, 2)}
for i in eval_eq_multi_branch_bound(eq, [range1], 0.1):
print i
def _eval_eq_direct(e, subs=None):
'''do the actual interval evaluation'''
rv = None
if not isinstance(e, Expr):
raise RuntimeError("Expected sympy Expr: " + repr(e))
if isinstance(e, Symbol):
if subs == None:
raise RuntimeError("Symbol '" + str(e) + "' found but no substitutions were provided")
val = subs.get(str(e))
if val == None:
raise RuntimeError("No substitution was provided for symbol '" + str(e) + "'")
rv = val
elif isinstance(e, Number):
rv = interval(Float(e))
elif isinstance(e, Mul):
rv = interval(1)
for child in e.args:
rv *= _eval_eq_direct(child, subs)
elif isinstance(e, Add):
rv = interval(0)
for child in e.args:
rv += _eval_eq_direct(child, subs)
elif isinstance(e, Pow):
term = _eval_eq_direct(e.args[0], subs)
exponent = _eval_eq_direct(e.args[1], subs)
rv = term**exponent
else:
# interval function evaluation (like sin)
func_map = [(sin, iv.sin), (cos, iv.cos), (tan, iv.tan)]
for entry in func_map:
t = entry[0] # type
f = entry[1] # function to call
if isinstance(e, t):
inner_arg = _eval_eq_direct(e.args[0], subs)
rv = f(inner_arg)
break
if rv == None:
raise RuntimeError("Type '" + str(type(e)) + "' is not yet implemented for interval evaluation. " + \
"Subexpression was '" + str(e) + "'.")
return rv
def _basinhopping(e, subs):
'''use scipy basinhopping to get an underestimate
e is a sympy expression
subs is the substitution map
'''
symbol_list = []
limits = []
for var, lim in subs.items():
symbol_list.append(symbols(var))
limits.append(lim)
def eval_func(var_list):
'''eval func used for optimization'''
sub_list = {}
for i in xrange(len(var_list)):
sub_list[symbol_list[i]] = var_list[i]
return float(e.evalf(subs=sub_list))
i = scipy_optimize.opt(eval_func, limits, niter=10)
return interval(i[0], i[1])
def _eval_eq_branch_bound(e, subs, bound):
'''do branch and bound interval evaluation'''
rv = None
for var, i in subs.iteritems():
if i.delta > bound:
# recursive cases, use smaller bounds
bound_left = copy.deepcopy(subs)
bound_left[var] = interval(i.a, (i.a + i.b) / 2)
rv_left = _eval_eq_branch_bound(e, bound_left, bound)
bound_right = copy.deepcopy(subs)
bound_right[var] = interval((i.a + i.b)/2, i.b)
rv_right = _eval_eq_branch_bound(e, bound_right, bound)
rv = interval(min(rv_left.a, rv_right.a), max(rv_left.b, rv_right.b))
break
if rv == None:
# base case, interval was small enough
rv = _eval_eq_direct(e, subs)
return rv
