ExpressionFactorGraph

This API walkthrough introduces the wrapped classes ExpressionFactorGraph declared by ExpressionFactorGraph.h and demonstrates their principal Python operations.

Authors: Frank Dellaert, et al. (see THANKS for the full author list)

See LICENSE for the license information

try:
    import google.colab
    %pip install --quiet gtsam-develop
except ImportError:
    pass

import gtsam
import numpy as np
from gtsam.symbol_shorthand import L, X

Overview¶

The ExpressionFactorGraph class in GTSAM is a specialized factor graph designed to work with expressions. It extends the capabilities of a standard factor graph by allowing factors created from GTSAM expressions, that implement automatic differentiation. It creates ExpressionFactors.

Adding Expression Factors¶

use addExpressionFactor: This method allows the user to add a new factor to the graph based on a symbolic expression. The expression defines the relationship between the variables involved in the factor.

  template<typename T>
  void addExpressionFactor(const Expression<T>& h, const T& z,
      const SharedNoiseModel& R) {
    using F = ExpressionFactor<T>;
    push_back(std::allocate_shared<F>(Eigen::aligned_allocator<F>(), R, z, h));
  }

Python wrapper walkthrough¶

The following cell exercises the wrapped API directly.

print(gtsam.ExpressionFactorGraph.__init__.__doc__)
print([name for name in dir(gtsam.ExpressionFactorGraph) if not name.startswith('_')])