# What’s New in kcorrect 5¶

For this version the software has been migrated to pure Python. There is no longer a C or IDL interface. There are fewer high-level utilities as well; basically, more of the data preparation is left to the users. The new version does not require any environmental variables to be set.

The methodology is otherwise almost the same, using the same set of templates as v4.

The only methodological difference to the K-corrections is that the nonnegative least squares is performed with the SciPy NNLS function rather than the iterative method used in the past. Both methods solve the same minimization problem so the answers are very close to one another.

The stellar masses and absolute magnitudes are no longer referenced to $$h=1$$. Instead, they are given by default using the Planck18 version of the FlatLambdaCDM cosmology, with the Hubble Constant for that cosmology.

If you are still using v4, please look at its online documentation for more information.