def test_split_stochastic():
tau = 5 * ms
expr = Expression('(-v + I) / tau')
# No stochastic part
assert expr.split_stochastic() == (expr, None)
# No non-stochastic part -- note that it should return 0 and not None
expr = Expression('sigma*xi/tau**.5')
non_stochastic, stochastic = expr.split_stochastic()
assert sympy_equals(non_stochastic, 0)
assert 'xi' in stochastic
assert len(stochastic) == 1
assert sympy_equals(stochastic['xi'].code, 'sigma/tau**.5')
expr = Expression('(-v + I) / tau + sigma*xi/tau**.5')
non_stochastic, stochastic = expr.split_stochastic()
assert 'xi' in stochastic
assert len(stochastic) == 1
assert sympy_equals(non_stochastic.code, '(-v + I) / tau')
assert sympy_equals(stochastic['xi'].code, 'sigma/tau**.5')
expr = Expression('(-v + I) / tau + sigma*xi_1/tau**.5 + xi_2*sigma2/sqrt(tau_2)')
non_stochastic, stochastic = expr.split_stochastic()
assert set(stochastic.keys()) == {'xi_1', 'xi_2'}
assert sympy_equals(non_stochastic.code, '(-v + I) / tau')
assert sympy_equals(stochastic['xi_1'].code, 'sigma/tau**.5')
assert sympy_equals(stochastic['xi_2'].code, 'sigma2/tau_2**.5')
expr = Expression('-v / tau + 1 / xi')
assert_raises(ValueError, expr.split_stochastic)
def test_split_stochastic():
tau = 5 * ms
expr = Expression('(-v + I) / tau')
expr.resolve(['v', 'I'])
# No stochastic part
assert expr.split_stochastic() == (expr, None)
expr = Expression('(-v + I) / tau + sigma*xi/tau**.5')
expr.resolve(['v', 'I', 'sigma'])
non_stochastic, stochastic = expr.split_stochastic()
assert 'xi' in stochastic.identifiers
assert sympy_equals(non_stochastic.code, '(-v + I) / tau')
assert sympy_equals(stochastic.code, 'sigma*xi/tau**.5')
expr = Expression('-v / tau + 1 / xi')
assert_raises(ValueError, expr.split_stochastic)
