Sym v1.2.0

Source code for modulus.sym.eq.derivatives

# Copyright (c) 2023, NVIDIA CORPORATION & AFFILIATES. All rights reserved. # # Licensed under the Apache License, Version 2.0 (the “License”); # you may not use this file except in compliance with the License. # You may obtain a copy of the License at # # # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an “AS IS” BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. import itertools import torch import numpy as np import logging from torch.autograd import Function from modulus.sym.constants import diff from modulus.sym.key import Key from modulus.sym.node import Node from modulus.sym.eq.mfd import FirstDeriv, SecondDeriv, ThirdDeriv, ForthDeriv from typing import Dict, List, Set, Optional, Union, Callable Tensor = torch.Tensor logger = logging.getLogger(__name__) # ==== Autodiff ==== @torch.jit.script def gradient(y: torch.Tensor, x: List[torch.Tensor]) -> List[torch.Tensor]:  """  TorchScript function to compute the gradient of a tensor wrt multople inputs  """ grad_outputs: List[Optional[torch.Tensor]] = [torch.ones_like(y, device=y.device)] grad = torch.autograd.grad( [ y, ], x, grad_outputs=grad_outputs, create_graph=True, allow_unused=True, ) if grad is None: grad = [torch.zeros_like(xx) for xx in x] assert grad is not None grad = [g if g is not None else torch.zeros_like(x[i]) for i, g in enumerate(grad)] return grad 
[docs]class Derivative(torch.nn.Module): """ Module to compute derivatives using backward automatic differentiation """ def __init__(self, bwd_derivative_dict: Dict[Key, List[Key]]): """ Constructor of the Derivative class. Parameters ---------- inputs : List[Key] A list of keys of the available variables to compute the required variables This list should contain both the variables that need to be differentiated and the variables to differentiate with respect to. derivatives : List[Key] A list of keys of the required derivatives """ super().__init__() self.gradient_dict: Dict[str, Dict[str, int]] = { str(k): {str(w): w.size for w in v} for k, v in bwd_derivative_dict.items() } self.gradient_names: Dict[str, List[str]] = { k: [diff(k, der) for der in v.keys()] for k, v in self.gradient_dict.items() } self.nvtx_str: str = f“Auto-Diff Node: {list(self.gradient_dict.keys())}" @staticmethod def prepare_input( input_variables: Dict[str, torch.Tensor], mask: List[str] ) -> List[torch.Tensor]: return [input_variables[x] for x in mask] @staticmethod def dict_output( output_tensors: List[torch.Tensor], sizes: List[str], var_name: str ) -> Dict[str, torch.Tensor]: return {diff(var_name, name): output_tensors[i] for i, name in enumerate(sizes)}
[docs] def forward(self, input_var: Dict[str, torch.Tensor]) -> Dict[str, torch.Tensor]: output_var = {} for var_name, grad_sizes in self.gradient_dict.items(): var = input_var[var_name] grad_var = self.prepare_input(input_var, grad_sizes.keys()) grad = gradient(var, grad_var) grad_dict = { name: grad[i] for i, name in enumerate(self.gradient_names[var_name]) } output_var.update(grad_dict) return output_var

@classmethod def make_node(cls, inputs: List[Key], derivatives: List[Key], name=None, jit=True): derivatives = [d for d in derivatives if d not in inputs] bwd_derivative_dict = _derivative_dict(inputs, derivatives, forward=False) output_derivatives = [] for key, value in bwd_derivative_dict.items(): output_derivatives += [ Key(, key.size, key.derivatives + [x]) for x in value ] evaluate = cls(bwd_derivative_dict) nvtx_str = evaluate.nvtx_str if jit: evaluate = torch.jit.script(evaluate) derivative_node = Node( inputs, output_derivatives, evaluate, name=(nvtx_str if name is None else str(name)), ) return derivative_node

def _derivative_dict(var, derivatives, forward=False): needed = derivatives while True: # break apart diff to see if first order needed break_loop = True for n in needed: l_n = Key(, n.size, n.derivatives[:-1]) if (len(n.derivatives) > 1) and l_n not in needed and l_n not in var: needed.append(l_n) break_loop = False if break_loop: break current = var diff_dict = {} for c, n in itertools.product(current, needed): c_under_n = Key(, n.size, n.derivatives[0 : len(c.derivatives)]) if (c == c_under_n) and (len(n.derivatives) == len(c.derivatives) + 1): if forward: if n.derivatives[len(c.derivatives)] not in diff_dict: diff_dict[n.derivatives[len(c.derivatives)]] = set() diff_dict[n.derivatives[len(c.derivatives)]].add(c) else: if c not in diff_dict: diff_dict[c] = set() diff_dict[c].add(n.derivatives[len(c.derivatives)]) diff_dict = {key: list(value) for key, value in diff_dict.items()} return diff_dict # ==== Meshless finite derivs ====

[docs]class MeshlessFiniteDerivative(torch.nn.Module): """ Module to compute derivatives using meshless finite difference Parameters ---------- model : torch.nn.Module Forward torch module for calculating stencil values derivatives : List[Key] List of derivative keys to calculate dx : Union[float, Callable] Spatial discretization of all axis, can be function with parameter `count` which is the number of forward passes for dynamically adjusting dx order : int, optional Order of derivative, by default 2 max_batch_size : Union[int, None], optional Max batch size of stencil calucations, by default uses batch size of inputs double_cast : bool, optional Cast fields to double precision to calculate derivatives, by default True jit : bool, optional Use torch script for finite deriv calcs, by default True """ def __init__( self, model: torch.nn.Module, derivatives: List[Key], dx: Union[float, Callable], order: int = 2, max_batch_size: Union[int, None] = None, double_cast: bool = True, input_keys: Union[List[Key], None] = None, ): super().__init__() self.model = model self._dx = dx self.double_cast = double_cast self.max_batch_size = max_batch_size self.input_keys = input_keys self.count = 0 self.derivatives = {1: [], 2: [], 3: [], 4: []} for key in derivatives: try: self.derivatives[len(key.derivatives)].append(key) except: raise NotImplementedError( f"{len(key.derivatives)}th derivatives not supported” ) self.first_deriv = FirstDeriv(self.derivatives[1], self.dx, order=order) self.second_deriv = SecondDeriv(self.derivatives[2], self.dx, order=order) self.third_deriv = ThirdDeriv(self.derivatives[3], self.dx, order=order) self.forth_deriv = ForthDeriv(self.derivatives[4], self.dx, order=order)
[docs] @torch.jit.ignore() def forward(self, inputs: Dict[str, torch.Tensor]) -> Dict[str, torch.Tensor]: self.count += 1 dx = self.dx self.first_deriv.dx = dx self.second_deriv.dx = dx self.third_deriv.dx = dx self.forth_deriv.dx = dx torch.cuda.nvtx.range_push(f“Calculating meshless finite derivatives”) # Assemble global stencil global_stencil = [] for deriv in [ self.first_deriv, self.second_deriv, self.third_deriv, self.forth_deriv, ]: stencil_list = deriv.stencil # Remove centered stencil points if already in input dictionary for i, point in enumerate(stencil_list): if point.split("::")[1] == str(0) and point.split("::")[0] in inputs: stencil_list.pop(i) global_stencil.extend(stencil_list) global_stencil = list(set(global_stencil)) # Number of stencil points to fit into a forward pass input_batch_size = next(iter(inputs.values())).size(0) if self.max_batch_size is None: num_batch = 1 else: num_batch = max([self.max_batch_size, input_batch_size]) // input_batch_size # Stencil forward passes index = 0 finite_diff_inputs = inputs.copy() while index < len(global_stencil): torch.cuda.nvtx.range_push(f“Running stencil forward pass”) # Batch up stencil inputs stencil_batch = [global_stencil[index]] index += 1 for j in range(1, min([len(global_stencil) - (index - 1), num_batch])): stencil_batch.append(global_stencil[index]) index += 1 model_inputs = self._get_stencil_input(inputs, stencil_batch) # Model forward outputs = self.model(model_inputs) # Dissassemble batched inputs for key, value in outputs.items(): outputs[key] = torch.split(value.view(-1, len(stencil_batch)), 1, dim=1) for i, stencil_str in enumerate(stencil_batch): for key, value in outputs.items(): finite_diff_inputs[f"{key}>>{stencil_str}"] = value[i] torch.cuda.nvtx.range_pop() # Calc finite diff grads torch.cuda.nvtx.range_push(f“Calc finite difference”) if self.double_cast: # Cast tensors to doubles for finite diff calc for key, value in finite_diff_inputs.items(): finite_diff_inputs[key] = value.double() outputs_first = self.first_deriv(finite_diff_inputs) outputs_second = self.second_deriv(finite_diff_inputs) outputs_third = self.third_deriv(finite_diff_inputs) outputs_forth = self.forth_deriv(finite_diff_inputs) outputs = inputs if self.double_cast: dtype = torch.get_default_dtype() for key, value in outputs_first.items(): outputs_first[key] = value.type(dtype) for key, value in outputs_second.items(): outputs_second[key] = value.type(dtype) for key, value in outputs_third.items(): outputs_third[key] = value.type(dtype) for key, value in outputs_forth.items(): outputs_forth[key] = value.type(dtype) outputs = { **inputs, **outputs_first, **outputs_second, **outputs_third, **outputs_forth, } torch.cuda.nvtx.range_pop() torch.cuda.nvtx.range_pop() return outputs

@property def dx(self): if hasattr(self._dx, “__call__”): return self._dx(self.count) else: return self._dx def _get_stencil_input( self, inputs: Dict[str, Tensor], stencil_strs: List[str] ) -> Dict[str, Tensor]: """Creates a copy of the inputs tensor and adjusts its values based on the stencil str. Parameters ---------- inputs : Dict[str, Tensor] Input tensor dictionary stencil_strs : List[str] batch list of stencil string from derivative class Returns ------- Dict[str, Tensor] Modified input tensor dictionary Example ------- A stencil string `x::1` will modify inputs[‘x’] = inputs[‘x’] + dx A stencil string `y::-1,z::1` will modify inputs[‘y’] = inputs[‘y’] - dx, inputs[‘z’] = inputs[‘z’] + dx """ if self.input_keys is None: outputs = inputs.copy() else: outputs = {str(key): inputs[str(key)].clone() for key in self.input_keys} for key, value in outputs.items(): outputs[key] = value.repeat(1, len(stencil_strs)) for i, stencil_str in enumerate(stencil_strs): # Loop through points for point in stencil_str.split("&&"): var_name = point.split("::")[0] spacing = int(point.split("::")[1]) outputs[var_name][:, i] = outputs[var_name][:, i] + spacing * self.dx for key, value in outputs.items(): outputs[key] = value.view(-1, 1) return outputs

[docs] @classmethod def make_node( cls, node_model: Union[Node, torch.nn.Module], derivatives: List[Key], dx: Union[float, Callable], order: int = 2, max_batch_size: Union[int, None] = None, name: str = None, double_cast: bool = True, input_keys: Union[List[Key], List[str], None] = None, ): """Makes a meshless finite derivative node. Parameters ---------- node_model : Union[Node, torch.nn.Module] Node or torch.nn.Module for computing FD stencil values. Part of the inputs to this model should consist of the independent variables and output the functional value derivatives : List[Key] List of derivatives to be computed dx : Union[float, Callable] Spatial discretization for finite diff calcs, can be function order : int, optional Order of accuracy of finite diff calcs, by default 2 max_batch_size : Union[int, None], optional Maximum batch size to used with the stenicl foward passes, by default None name : str, optional Name of node, by default None double_cast : bool, optional Cast tensors to double precision for derivatives, by default True input_keys : Union[List[Key], List[str], None], optional List of input keys to be used for input of forward model. Should be used if node_model is not a :obj:`Node`, by default None """ # We have two sets of input keys: # input_keys: which are the list of inputs to the model for stencil points # mfd_input_keys: input keys for the MFD node if input_keys is None: input_keys = [] mfd_input_keys = [] else: input_keys = [str(key) for key in input_keys] mfd_input_keys = [str(key) for key in input_keys] for derivative in derivatives: mfd_input_keys.append( for dstr in derivative.derivatives: mfd_input_keys.append( input_keys.append( if isinstance(node_model, Node): model = node_model.evaluate input_keys = input_keys + [str(key) for key in node_model.inputs] else: model = node_model # Remove duplicate keys mfd_input_keys = Key.convert_list(list(set(mfd_input_keys))) input_keys = Key.convert_list(list(set(input_keys))) evaluate = cls( model, derivatives, dx=dx, order=order, max_batch_size=max_batch_size, double_cast=double_cast, input_keys=input_keys, ) derivative_node = Node( mfd_input_keys, derivatives, evaluate, name=( “Meshless-Finite-Derivative Node” + "" if name is None else f": {name}" ), ) return derivative_node
© Copyright 2023, NVIDIA Modulus Team. Last updated on Jan 25, 2024.