def use_points_for_interpolation(self, cNrm, mNrm, interpolator):
"""
Make a basic solution object with a consumption function and marginal
value function (unconditional on the preference shock).
Parameters
----------
cNrm : np.array
Consumption points for interpolation.
mNrm : np.array
Corresponding market resource points for interpolation.
interpolator : function
A function that constructs and returns a consumption function.
Returns
-------
solution_now : ConsumerSolution
The solution to this period's consumption-saving problem, with a
consumption function, marginal value function, and minimum m.
"""
# Make the preference-shock specific consumption functions
PrefShkCount = self.PrefShkVals.size
cFunc_list = []
for j in range(PrefShkCount):
MPCmin_j = self.MPCminNow * self.PrefShkVals[j]**(1.0 / self.CRRA)
cFunc_this_shock = LowerEnvelope(
LinearInterp(
mNrm[j, :],
cNrm[j, :],
intercept_limit=self.hNrmNow * MPCmin_j,
slope_limit=MPCmin_j,
),
self.cFuncNowCnst,
)
cFunc_list.append(cFunc_this_shock)
# Combine the list of consumption functions into a single interpolation
cFuncNow = LinearInterpOnInterp1D(cFunc_list, self.PrefShkVals)
# Make the ex ante marginal value function (before the preference shock)
m_grid = self.aXtraGrid + self.mNrmMinNow
vP_vec = np.zeros_like(m_grid)
for j in range(
PrefShkCount): # numeric integration over the preference shock
vP_vec += (self.uP(cFunc_list[j](m_grid)) * self.PrefShkPrbs[j] *
self.PrefShkVals[j])
vPnvrs_vec = self.uPinv(vP_vec)
vPfuncNow = MargValueFuncCRRA(LinearInterp(m_grid, vPnvrs_vec),
self.CRRA)
# Store the results in a solution object and return it
solution_now = ConsumerSolution(cFunc=cFuncNow,
vPfunc=vPfuncNow,
mNrmMin=self.mNrmMinNow)
return solution_now
def post_solve(self):
self.solution_fast = deepcopy(self.solution)
if self.cycles == 0:
cycles = 1
else:
cycles = self.cycles
self.solution[-1] = self.solution_terminal_cs
for i in range(cycles):
for j in range(self.T_cycle):
solution = self.solution[i * self.T_cycle + j]
# Define the borrowing constraint (limiting consumption function)
cFuncNowCnst = LinearInterp(
np.array([solution.mNrmMin, solution.mNrmMin + 1]),
np.array([0.0, 1.0]),
)
"""
Constructs a basic solution for this period, including the consumption
function and marginal value function.
"""
if self.CubicBool:
# Makes a cubic spline interpolation of the unconstrained consumption
# function for this period.
cFuncNowUnc = CubicInterp(
solution.mNrm,
solution.cNrm,
solution.MPC,
solution.cFuncLimitIntercept,
solution.cFuncLimitSlope,
)
else:
# Makes a linear interpolation to represent the (unconstrained) consumption function.
# Construct the unconstrained consumption function
cFuncNowUnc = LinearInterp(
solution.mNrm,
solution.cNrm,
solution.cFuncLimitIntercept,
solution.cFuncLimitSlope,
)
# Combine the constrained and unconstrained functions into the true consumption function
cFuncNow = LowerEnvelope(cFuncNowUnc, cFuncNowCnst)
# Make the marginal value function and the marginal marginal value function
vPfuncNow = MargValueFuncCRRA(cFuncNow, self.CRRA)
# Pack up the solution and return it
consumer_solution = ConsumerSolution(
cFunc=cFuncNow,
vPfunc=vPfuncNow,
mNrmMin=solution.mNrmMin,
hNrm=solution.hNrm,
MPCmin=solution.MPCmin,
MPCmax=solution.MPCmax,
)
if self.vFuncBool:
vNvrsFuncNow = CubicInterp(
solution.mNrmGrid,
solution.vNvrs,
solution.vNvrsP,
solution.MPCminNvrs * solution.hNrm,
solution.MPCminNvrs,
)
vFuncNow = ValueFuncCRRA(vNvrsFuncNow, self.CRRA)
consumer_solution.vFunc = vFuncNow
if self.CubicBool or self.vFuncBool:
_searchFunc = (
_find_mNrmStECubic if self.CubicBool else _find_mNrmStELinear
)
# Add mNrmStE to the solution and return it
consumer_solution.mNrmStE = _add_mNrmStEIndNumba(
self.PermGroFac[j],
self.Rfree,
solution.Ex_IncNext,
solution.mNrmMin,
solution.mNrm,
solution.cNrm,
solution.MPC,
solution.MPCmin,
solution.hNrm,
_searchFunc,
)
self.solution[i * self.T_cycle + j] = consumer_solution
def solveConsMarkovALT(solution_next,IncomeDstn,LivPrb,DiscFac,CRRA,Rfree,PermGroFac,uPfac,
MrkvArray,BoroCnstArt,aXtraGrid,vFuncBool,CubicBool):
'''
Solves a single period consumption-saving problem with risky income and
stochastic transitions between discrete states, in a Markov fashion. Has
identical inputs as solveConsIndShock, except for a discrete
Markov transitionrule MrkvArray. Markov states can differ in their interest
factor, permanent growth factor, and income distribution, so the inputs Rfree,
PermGroFac, and IncomeDstn are arrays or lists specifying those values in each
(succeeding) Markov state.
Parameters
----------
solution_next : ConsumerSolution
The solution to next period's one period problem.
IncomeDstn : DiscreteDistribution
A representation of permanent and transitory income shocks that might
arrive at the beginning of next period.
LivPrb : float
Survival probability; likelihood of being alive at the beginning of
the succeeding period.
DiscFac : float
Intertemporal discount factor for future utility.
CRRA : float
Coefficient of relative risk aversion.
Rfree : np.array
Risk free interest factor on end-of-period assets for each Markov
state in the succeeding period.
PermGroFac : np.array
Expected permanent income growth factor at the end of this period
for each Markov state in the succeeding period.
uPfac : np.array
Scaling factor for (marginal) utility in each current Markov state.
MrkvArray : np.array
An NxN array representing a Markov transition matrix between discrete
states. The i,j-th element of MrkvArray is the probability of
moving from state i in period t to state j in period t+1.
BoroCnstArt: float or None
Borrowing constraint for the minimum allowable assets to end the
period with. If it is less than the natural borrowing constraint,
then it is irrelevant; BoroCnstArt=None indicates no artificial bor-
rowing constraint.
aXtraGrid: np.array
Array of "extra" end-of-period asset values-- assets above the
absolute minimum acceptable level.
vFuncBool: boolean
An indicator for whether the value function should be computed and
included in the reported solution. Not used.
CubicBool: boolean
An indicator for whether the solver should use cubic or linear inter-
polation. Not used.
Returns
-------
solution : ConsumerSolution
The solution to the single period consumption-saving problem. Includes
a consumption function cFunc (using cubic or linear splines), a marg-
inal value function vPfunc, a minimum acceptable level of normalized
market resources mNrmMin. All of these attributes are lists or arrays,
with elements corresponding to the current Markov state. E.g.
solution.cFunc[0] is the consumption function when in the i=0 Markov
state this period.
'''
# Get sizes of grids
aCount = aXtraGrid.size
StateCount = MrkvArray.shape[0]
# Loop through next period's states, assuming we reach each one at a time.
# Construct EndOfPrdvP_cond functions for each state.
BoroCnstNat_cond = []
EndOfPrdvPfunc_cond = []
for j in range(StateCount):
# Unpack next period's solution
vPfuncNext = solution_next.vPfunc[j]
mNrmMinNext = solution_next.mNrmMin[j]
# Unpack the income shocks
ShkPrbsNext = IncomeDstn[j].pmf
PermShkValsNext = IncomeDstn[j].X[0]
TranShkValsNext = IncomeDstn[j].X[1]
ShkCount = ShkPrbsNext.size
aXtra_tiled = np.tile(np.reshape(aXtraGrid, (aCount, 1)), (1, ShkCount))
# Make tiled versions of the income shocks
# Dimension order: aNow, Shk
ShkPrbsNext_tiled = np.tile(np.reshape(ShkPrbsNext, (1, ShkCount)), (aCount, 1))
PermShkValsNext_tiled = np.tile(np.reshape(PermShkValsNext, (1, ShkCount)), (aCount, 1))
TranShkValsNext_tiled = np.tile(np.reshape(TranShkValsNext, (1, ShkCount)), (aCount, 1))
# Find the natural borrowing constraint
aNrmMin_candidates = PermGroFac[j]*PermShkValsNext_tiled/Rfree[j]*(mNrmMinNext - TranShkValsNext_tiled[0, :])
aNrmMin = np.max(aNrmMin_candidates)
BoroCnstNat_cond.append(aNrmMin)
# Calculate market resources next period (and a constant array of capital-to-labor ratio)
aNrmNow_tiled = aNrmMin + aXtra_tiled
mNrmNext_array = Rfree[j]*aNrmNow_tiled/PermShkValsNext_tiled + TranShkValsNext_tiled
# Find marginal value next period at every income shock realization and every aggregate market resource gridpoint
vPnext_array = Rfree[j]*PermShkValsNext_tiled**(-CRRA)*vPfuncNext(mNrmNext_array)
# Calculate expectated marginal value at the end of the period at every asset gridpoint
EndOfPrdvP = DiscFac*np.sum(vPnext_array*ShkPrbsNext_tiled, axis=1)
# Make the conditional end-of-period marginal value function
EndOfPrdvPnvrs = EndOfPrdvP**(-1./CRRA)
EndOfPrdvPnvrsFunc = LinearInterp(np.insert(aNrmMin + aXtraGrid, 0, aNrmMin), np.insert(EndOfPrdvPnvrs, 0, 0.0))
EndOfPrdvPfunc_cond.append(MargValueFunc(EndOfPrdvPnvrsFunc, CRRA))
# Now loop through *this* period's discrete states, calculating end-of-period
# marginal value (weighting across state transitions), then construct consumption
# and marginal value function for each state.
cFuncNow = []
vPfuncNow = []
mNrmMinNow = []
for i in range(StateCount):
# Find natural borrowing constraint for this state
aNrmMin_candidates = np.zeros(StateCount) + np.nan
for j in range(StateCount):
if MrkvArray[i, j] > 0.: # Irrelevant if transition is impossible
aNrmMin_candidates[j] = BoroCnstNat_cond[j]
aNrmMin = np.nanmax(aNrmMin_candidates)
# Find the minimum allowable market resources
if BoroCnstArt is not None:
mNrmMin = np.maximum(BoroCnstArt, aNrmMin)
else:
mNrmMin = aNrmMin
mNrmMinNow.append(mNrmMin)
# Make tiled grid of aNrm
aNrmNow = aNrmMin + aXtraGrid
# Loop through feasible transitions and calculate end-of-period marginal value
EndOfPrdvP = np.zeros(aCount)
for j in range(StateCount):
if MrkvArray[i, j] > 0.:
temp = MrkvArray[i, j]*EndOfPrdvPfunc_cond[j](aNrmNow)
EndOfPrdvP += temp
EndOfPrdvP *= LivPrb[i] # Account for survival out of the current state
# Calculate consumption and the endogenous mNrm gridpoints for this state
cNrmNow = (EndOfPrdvP/uPfac[i])**(-1./CRRA)
mNrmNow = aNrmNow + cNrmNow
# Make a piecewise linear consumption function
c_temp = np.insert(cNrmNow, 0, 0.0) # Add point at bottom
m_temp = np.insert(mNrmNow, 0, aNrmMin)
cFuncUnc = LinearInterp(m_temp, c_temp)
cFuncCnst = LinearInterp(np.array([mNrmMin, mNrmMin+1.0]), np.array([0.0, 1.0]))
cFuncNow.append(LowerEnvelope(cFuncUnc,cFuncCnst))
# Construct the marginal value function using the envelope condition
m_temp = aXtraGrid + mNrmMin
c_temp = cFuncNow[i](m_temp)
uP = uPfac[i]*c_temp**(-CRRA)
vPnvrs = uP**(-1./CRRA)
vPnvrsFunc = LinearInterp(np.insert(m_temp, 0, mNrmMin), np.insert(vPnvrs, 0, 0.0))
vPfuncNow.append(MargValueFunc(vPnvrsFunc, CRRA))
# Pack up and return the solution
solution_now = ConsumerSolution(cFunc=cFuncNow, vPfunc=vPfuncNow, mNrmMin=mNrmMinNow)
return solution_now
def make_solution(self, cNrm, mNrm):
"""
Construct an object representing the solution to this period's problem.
Parameters
----------
cNrm : np.array
Array of normalized consumption values for interpolation. Each row
corresponds to a Markov state for this period.
mNrm : np.array
Array of normalized market resource values for interpolation. Each
row corresponds to a Markov state for this period.
Returns
-------
solution : ConsumerSolution
The solution to the single period consumption-saving problem. Includes
a consumption function cFunc (using cubic or linear splines), a marg-
inal value function vPfunc, a minimum acceptable level of normalized
market resources mNrmMin, normalized human wealth hNrm, and bounding
MPCs MPCmin and MPCmax. It might also have a value function vFunc
and marginal marginal value function vPPfunc. All of these attributes
are lists or arrays, with elements corresponding to the current
Markov state. E.g. solution.cFunc[0] is the consumption function
when in the i=0 Markov state this period.
"""
solution = (
ConsumerSolution()
) # An empty solution to which we'll add state-conditional solutions
# Calculate the MPC at each market resource gridpoint in each state (if desired)
if self.CubicBool:
dcda = self.EndOfPrdvPP / self.uPP(np.array(self.cNrmNow))
MPC = dcda / (dcda + 1.0)
self.MPC_temp = np.hstack(
(np.reshape(self.MPCmaxNow, (self.StateCount, 1)), MPC)
)
interpfunc = self.make_cubic_cFunc
else:
interpfunc = self.make_linear_cFunc
# Loop through each current period state and add its solution to the overall solution
for i in range(self.StateCount):
# Set current-period-conditional human wealth and MPC bounds
self.hNrmNow_j = self.hNrmNow[i]
self.MPCminNow_j = self.MPCminNow[i]
if self.CubicBool:
self.MPC_temp_j = self.MPC_temp[i, :]
# Construct the consumption function by combining the constrained and unconstrained portions
self.cFuncNowCnst = LinearInterp(
[self.mNrmMin_list[i], self.mNrmMin_list[i] + 1.0], [0.0, 1.0]
)
cFuncNowUnc = interpfunc(mNrm[i, :], cNrm[i, :])
cFuncNow = LowerEnvelope(cFuncNowUnc, self.cFuncNowCnst)
# Make the marginal value function and pack up the current-state-conditional solution
vPfuncNow = MargValueFuncCRRA(cFuncNow, self.CRRA)
solution_cond = ConsumerSolution(
cFunc=cFuncNow, vPfunc=vPfuncNow, mNrmMin=self.mNrmMinNow
)
if (
self.CubicBool
): # Add the state-conditional marginal marginal value function (if desired)
solution_cond = self.add_vPPfunc(solution_cond)
# Add the current-state-conditional solution to the overall period solution
solution.append_solution(solution_cond)
# Add the lower bounds of market resources, MPC limits, human resources,
# and the value functions to the overall solution
solution.mNrmMin = self.mNrmMin_list
solution = self.add_MPC_and_human_wealth(solution)
if self.vFuncBool:
vFuncNow = self.make_vFunc(solution)
solution.vFunc = vFuncNow
# Return the overall solution to this period
return solution
def makeBasicSolution(self, EndOfPrdvP, aNrm, wageShkVals, prefShkVals):
'''
Given end of period assets and end of period marginal value, construct
the basic solution for this period.
Parameters
----------
EndOfPrdvP : np.array
Array of end-of-period marginal values.
aNrm : np.array
Array of end-of-period asset values that yield the marginal values
in EndOfPrdvP.
wageShkVals : np.array
Array of this period transitory wage shock values.
prefShkVals : np.array
Array of this period preference shock values.
Returns
-------
solution_now : ConsumerSolution
The solution to this period's consumption-saving problem, with a
consumption function, marginal value function.
'''
num_pref_shocks = len(prefShkVals)
num_wage_shocks = len(wageShkVals)
cFuncBaseByPref_list = []
vPFuncBaseByPref_list = []
lFuncBaseByPref_list = []
for i in range(num_wage_shocks):
cFuncBaseByPref_list.append([])
vPFuncBaseByPref_list.append([])
lFuncBaseByPref_list.append([])
for j in range(num_pref_shocks):
c_temp = self.uPinv(EndOfPrdvP / prefShkVals[j])
l_temp = self.LabSupply(wageShkVals[i] * EndOfPrdvP)
b_temp = c_temp + aNrm - l_temp * wageShkVals[i]
if wageShkVals[i] == 0.0:
c_temp = np.insert(c_temp, 0, 0., axis=-1)
l_temp = np.insert(l_temp, 0, 0.0, axis=-1)
b_temp = np.insert(b_temp, 0, 0.0, axis=-1)
lFuncBaseByPref_list[i].append(
LinearInterp(b_temp, l_temp, lower_extrap=True))
cFunc1 = LinearInterp(b_temp, c_temp, lower_extrap=True)
cFunc2 = LinearInterp(b_temp,
l_temp * wageShkVals[i] + b_temp,
lower_extrap=True)
cFuncBaseByPref_list[i].append(LowerEnvelope(cFunc1, cFunc2))
pseudo_inverse_vPfunc1 = LinearInterp(
b_temp,
prefShkVals[j]**(-1.0 / self.CRRA) * c_temp,
lower_extrap=True)
pseudo_inverse_vPfunc2 = LinearInterp(
b_temp,
prefShkVals[j]**(-1.0 / self.CRRA) *
(l_temp * wageShkVals[i] + b_temp),
lower_extrap=True)
pseudo_inverse_vPfunc = LowerEnvelope(pseudo_inverse_vPfunc1,
pseudo_inverse_vPfunc2)
vPFuncBaseByPref_list[i].append(
MargValueFunc(pseudo_inverse_vPfunc, self.CRRA))
cFuncNow = BilinearInterpOnInterp1D(cFuncBaseByPref_list, wageShkVals,
prefShkVals)
vPfuncNow = BilinearInterpOnInterp1D(vPFuncBaseByPref_list,
wageShkVals, prefShkVals)
lFuncNow = BilinearInterpOnInterp1D(lFuncBaseByPref_list, wageShkVals,
prefShkVals)
# Pack up and return the solution
solution_now = ConsumerSolution(cFunc=cFuncNow, vPfunc=vPfuncNow)
solution_now.lFunc = lFuncNow
return solution_now