How to smooth data to a negative curve

I'm looking to smooth out some experimental data.

Some recorded data points go upwards, altough this isn't possible for the given subject. Is there a way to smooth my data and at the same time, make sure that x_i < x_i-1, i.e., always with a negative curve.

[Jonathan Couture]

For a bit more context, I've already used the 'smoothdata' command on it, and this is the output.

Answer 1

[Matt J]

Thie File Exchange submission allows you to do spline smoothing with monotonicity constraints:

https://www.mathworks.com/matlabcentral/fileexchange/24443-slm-shape-language-modeling

You can also do Gaussian+constant fitting with the following File Exchange submission, and with bound constraints on the mu parameter:

https://www.mathworks.com/matlabcentral/fileexchange/69116-gaussfitn?s_tid=srchtitle

With mu<=0, that would ensure monotonic descent over the range of your data.