*Last updated: 2023-03-16.*
# Module: tf_quant_finance.experimental.american_option_pricing.andersen_lake.common
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Helper functions for calculating American option prices.
## Modules
[`types`](../../../../tf_quant_finance/types.md) module: Types module.
## Functions
[`d_minus(...)`](../../../../tf_quant_finance/experimental/american_option_pricing/andersen_lake/d_minus.md)
[`d_plus(...)`](../../../../tf_quant_finance/experimental/american_option_pricing/andersen_lake/d_plus.md)
[`divide_with_positive_denominator(...)`](../../../../tf_quant_finance/experimental/american_option_pricing/andersen_lake/divide_with_positive_denominator.md): Safely divides by a denominator which is mathematically always positive, but numerically can be zero.
[`machine_eps(...)`](../../../../tf_quant_finance/experimental/american_option_pricing/andersen_lake/machine_eps.md): Returns the machine epsilon for the supplied dtype.
[`standard_normal_cdf(...)`](../../../../tf_quant_finance/experimental/american_option_pricing/andersen_lake/standard_normal_cdf.md)