# Simulating dataΒΆ

Simulating a data set normally involves:

- evaluate the model
- add in noise

This may need to be repeated several times for complex models, such as when different components have different noise models or the noise needs to be added before evaluation by a component.

The model evaluation would be performed using the techniques
described in this section, and then the noise term can be
handled with `sherpa.utils.poisson_noise()`

or routines from
NumPy or SciPy to evaluate noise, such as `numpy.random.standard_normal`

.

```
>>> import numpy as np
>>> from sherpa.models.basic import Polynom1D
>>> np.random.seed(235)
>>> x = np.arange(10, 100, 12)
>>> mdl = Polynom1D('mdl')
>>> mdl.offset = 35
>>> mdl.c1 = 0.5
>>> mdl.c2 = 0.12
>>> ymdl = mdl(x)
>>> from sherpa.utils import poisson_noise
>>> ypoisson = poisson_noise(ymdl)
>>> from numpy.random import standard_normal, normal
>>> yconst = ymdl + standard_normal(ymdl.shape) * 10
>>> ydata = ymdl + normal(scale=np.sqrt(ymdl))
```