---
title: ForwardEulerSolver (v0.46)
description: API reference for qiskit.algorithms.time_evolvers.variational.ForwardEulerSolver in qiskit v0.46
source: https://eu-de.quantum.cloud.ibm.com/docs/en/api/qiskit/0.46/qiskit.algorithms.time_evolvers.variational.ForwardEulerSolver
---

# ForwardEulerSolver

*class* `qiskit.algorithms.time_evolvers.variational.ForwardEulerSolver(function, t0, y0, t_bound, vectorized=False, support_complex=False, num_t_steps=15)`

[GitHub](https://github.com/qiskit/qiskit/tree/stable/0.46/qiskit/algorithms/time_evolvers/variational/solvers/ode/forward_euler_solver.py)

Bases: `OdeSolver`

Forward Euler ODE solver.

Forward Euler ODE solver that implements an interface from SciPy.

**Parameters**

- **function** ([*Callable*](https://docs.python.org/3/library/collections.abc.html#collections.abc.Callable)) – Right-hand side of the system. The calling signature is `fun(t, y)`. Here `t` is a scalar, and there are two options for the ndarray `y`: It can either have shape (n,); then `fun` must return array\_like with shape (n,). Alternatively it can have shape (n, k); then `fun` must return an array\_like with shape (n, k), i.e., each column corresponds to a single column in `y`. The choice between the two options is determined by vectorized argument (see below). The vectorized implementation allows a faster approximation of the Jacobian by finite differences (required for this solver).
- **t0** ([*float*](https://docs.python.org/3/library/functions.html#float)) – Initial time.
- **y0** ([*Sequence*](https://docs.python.org/3/library/collections.abc.html#collections.abc.Sequence)) – Initial state.
- **t\_bound** ([*float*](https://docs.python.org/3/library/functions.html#float)) – Boundary time - the integration won’t continue beyond it. It also determines the direction of the integration.
- **vectorized** ([*bool*](https://docs.python.org/3/library/functions.html#bool)) – Whether `fun` is implemented in a vectorized fashion. Default is False.
- **support\_complex** ([*bool*](https://docs.python.org/3/library/functions.html#bool)) – Whether integration in a complex domain should be supported. Generally determined by a derived solver class capabilities. Default is False.
- **num\_t\_steps** ([*int*](https://docs.python.org/3/library/functions.html#int)) – Number of time steps for the forward Euler method.

## Attributes

### TOO\_SMALL\_STEP

Default value: `'Required step size is less than spacing between numbers.'`

### step\_size