# SimPEG 0.15.1 Release Notes#

August 27th, 2021

This patch release contains several small bug fixes and improvements to the code base.

## Updates#

We now have a simple depth weighting function that can be used as cell weights for inversions. It is based off of the common potential fields definition:

```
wz = 1/(z - z_0)**(q/2)
```

The way SimPEG handles the definition of standard deviation calculated from the mix of relative error and noise levels is slightly changed to respect a more statistically accurate combination of the two components. It is now:

```
standard_deviation = sqrt(noise_level**2 + (relative_error * abs(d_obs))**2)
```

In addition,

Removed a bit of dead code

Fixed some typos in documentation

Removed all references to old numpy matrix class and replaced with appropriate array functions.

Added clarification to the gravity examples explaining why SimPEG’s gravity module looks backwards.

removed some internal references to deprecated properties

## Contributors#

This is a combination of contributors and reviewers who’ve made contributions towards this release (in no particular order).

## Pull requests#

#1004: Depth weighting function in “model_utils.py”

#1009: Fix PGI gallery example

#1016: Remove dead code

#1019: Update receivers.py

#1022: Change definition of standard deviation

#1024: Add notes to gravity examples

#1025: Updates to fix the test errors

#1026: Replace np.matlib.repmat by np.tile

#1027: Replace np.matrix by regular ndarrays

#1029: Fix Typo in static_utils.py

#1034: rename .freqs to frequencies

#1035: 0.15.1 Release Notes