*Last updated: 2023-03-16.*
# tf_quant_finance.math.pde.steppers.composite_stepper.composite_scheme_step
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Composes two time marching schemes.
```python
tf_quant_finance.math.pde.steppers.composite_stepper.composite_scheme_step(
first_scheme_steps, first_scheme, second_scheme
)
```
Applies a step of parabolic PDE solver using `first_scheme` if number of
performed steps is less than `first_scheme_steps`, and using `second_scheme`
otherwise.
#### Args:
* `first_scheme_steps`: A Python integer. Number of steps to apply
`first_scheme` on.
* `first_scheme`: First time marching scheme (see `time_marching_scheme`
argument of `parabolic_equation_step`).
* `second_scheme`: Second time marching scheme (see `time_marching_scheme`
argument of `parabolic_equation_step`).
#### Returns:
Callable to be used in finite-difference PDE solvers (see fd_solvers.py).