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 FEMTIC is a 3-D magnetotelluric inversion code based on the following studies. 
 FEMTIC was made using object-oriented programming with C++.
 
-Y. Usui, 3-D inversion of magnetotelluric data using unstructured tetrahedral elements: applicability to data affected by topography, Geophys. J. Int., 202 (2): 828-849, https://doi.org/10.1093/gji/ggv186, 2015.
+*Y. Usui, 3-D inversion of magnetotelluric data using unstructured tetrahedral elements: applicability to data affected by topography, Geophys. J. Int., 202 (2): 828-849, https://doi.org/10.1093/gji/ggv186, 2015.*
 
-Y. Usui, Y. Ogawa, K. Aizawa, W. Kanda, T. Hashimoto, T. Koyama, Y. Yamaya and T. Kagiyama, Three-dimensional resistivity structure of Asama Volcano revealed by data-space magnetotelluric inversion using unstructured tetrahedral elements, Geophys. J. Int., 208 (3): 1359-1372, https://doi.org/10.1093/gji/ggw459, 2017.
+*Y. Usui, Y. Ogawa, K. Aizawa, W. Kanda, T. Hashimoto, T. Koyama, Y. Yamaya and T. Kagiyama, Three-dimensional resistivity structure of Asama Volcano revealed by data-space magnetotelluric inversion using unstructured tetrahedral elements, Geophys. J. Int., 208 (3): 1359-1372, https://doi.org/10.1093/gji/ggw459, 2017.*
 
-Y. Usui, T. Kasaya, Y. Ogawa and H. Iwamoto, Marine magnetotelluric inversion with an unstructured tetrahedral mesh, Geophys. J. Int., 214(2): 952-974, https://doi.org/10.1093/gji/ggy171, 2018.
+*Y. Usui, T. Kasaya, Y. Ogawa and H. Iwamoto, Marine magnetotelluric inversion with an unstructured tetrahedral mesh, Geophys. J. Int., 214(2): 952-974, https://doi.org/10.1093/gji/ggy171, 2018.*
 
 The website of FEMTIC:
 https://sites.google.com/view/yoshiyausui/femtic
@@ -22,3 +22,14 @@ Parallel computation: Hybrid MPI/OpenMP parallel calculation can be used.
 
 Model parameter: Subsurface electrical resistivity and distortion matrix of galvanic distortion.
 
+# Release note
+**v4.1** Nov. 9, 2021 This new version supports difference filter. The error calculation of log10(apparent resistivity) is modified. Rotation angles of distortion matrix are limited to from -90 to 90 (deg.) when gains and rotations of galvanic distortion are estimated.
+
+**v4.0** Jun. 3, 2021 This new version supports non-conforming deformed hexahedral mesh.
+
+**v3.5** Jan. 11, 2021 This new version supports observed data of apparent resistivity and phase and unsymmetric roughening matrix.
+
+**v3.4.7** Sep. 4, 2020 The integer indices into the multiple right-hand-side vectors and solution vectors were changed from 32-bit to 64-bit.
+
+**v3.4.6** Sep. 2, 2020 This version allows us to make resistivity of every individual subsurface element to be a different model parameter, in analogy with other 3-D inversion code.
+