# Frequently Asked Questions¶

A list of common questions.

## What’s the best way to ask for help or submit a bug report?¶

See Getting Help.

## Why did my script break when upgrading from lmfit 0.8.3 to 0.9.0?¶

## I get import errors from IPython¶

If you see something like:

```
from IPython.html.widgets import Dropdown
ImportError: No module named 'widgets'
```

then you need to install the `ipywidgets`

package, try: `pip install ipywidgets`

.

## How can I fit multi-dimensional data?¶

The fitting routines accept data arrays that are one dimensional and double precision. So you need to convert the data and model (or the value returned by the objective function) to be one dimensional. A simple way to do this is to use numpy.ndarray.flatten, for example:

```
def residual(params, x, data=None):
....
resid = calculate_multidim_residual()
return resid.flatten()
```

## How can I fit multiple data sets?¶

As above, the fitting routines accept data arrays that are one dimensional and double precision. So you need to convert the sets of data and models (or the value returned by the objective function) to be one dimensional. A simple way to do this is to use numpy.concatenate. As an example, here is a residual function to simultaneously fit two lines to two different arrays. As a bonus, the two lines share the ‘offset’ parameter:

```
import numpy as np
def fit_function(params, x=None, dat1=None, dat2=None):
model1 = params['offset'] + x * params['slope1']
model2 = params['offset'] + x * params['slope2']
resid1 = dat1 - model1
resid2 = dat2 - model2
return np.concatenate((resid1, resid2))
```

## How can I fit complex data?¶

As with working with multi-dimensional data, you need to convert your data and model (or the value returned by the objective function) to be double precision floating point numbers. The simplest approach is to use numpy.ndarray.view, perhaps like:

```
import numpy as np
def residual(params, x, data=None):
....
resid = calculate_complex_residual()
return resid.view(np.float)
```

## Can I constrain values to have integer values?¶

Basically, no. None of the minimizers in lmfit support integer programming. They all (I think) assume that they can make a very small change to a floating point value for a parameters value and see a change in the value to be minimized.