Update README.md

README.md

@@ -18,16 +18,19 @@ Petersson, N. Anders, Sjogreen, Bjorn, Tang, Houjun, & Pankajakshan, Ramesh. (20
 
 Primary References
 ------------------
-Sjögreen, B.; Petersson, N.A. (2012), A Fourth Order Accurate Finite Difference Scheme for the Elastic Wave Equation in Second Order Formulation, Journal of Scientific Computing, 52 (1) , 17-48, doi: 10.1007/s10915-011-9531-1, url: http://link.springer.com/10.1007/s10915-011-9531-1
+Zhang, L.;  Wang, S.; and Petersson, N.A. (2021), Elastic Wave Propagation in Curvilinear Coordinates with Mesh Refinement Interfaces by a Fourth Order Finite Difference Method, SIAM J. Sci. Comp.  43(2) pp. A1472-A1496. doi:10.1137/20M1339702
 
-Petersson, N.A.; Sjögreen, B. (2012), Stable and efficient modeling of anelastic attenuation in seismic wave propagation, Communications in Computational Physics, 12 (01) , 193-225
+Petersson, N.A.; Sjögreen, B. (2015), Wave propagation in anisotropic elastic materials and curvilinear coordinates using a summation-by-parts finite difference method, Journal of Computational Physics, 299, 820-841, doi: 10.1016/j.jcp.2015.07.023, url: http://linkinghub.elsevier.com/retrieve/pii/S0021999115004684
 
-Petersson, N.A.; Sjögreen, B.; Tang, H. (2023), User's guide to SW4, version 3.0, LLNL-SM-741439 (LLNL-SM-741439)
+Petersson, N.A.; Sjögreen, B. (2012), Stable and efficient modeling of anelastic attenuation in seismic wave propagation, Communications in Computational Physics, 12 (01), 193-225
+
+Sjögreen, B.; Petersson, N.A. (2012), A Fourth Order Accurate Finite Difference Scheme for the Elastic Wave Equation in Second Order Formulation, Journal of Scientific Computing, 52 (1), 17-48, doi: 10.1007/s10915-011-9531-1, url: http://link.springer.com/10.1007/s10915-011-9531-1
 
-Petersson, N.A.; Sjögreen, B. (2015), Wave propagation in anisotropic elastic materials and curvilinear coordinates using a summation-by-parts finite difference method, Journal of Computational Physics, 299, 820-841, doi: 10.1016/j.jcp.2015.07.023, url: http://linkinghub.elsevier.com/retrieve/pii/S0021999115004684
 
-Zhang, L.;  Wang, S.; and Petersson, N.A. (2021), Elastic Wave Propagation in Curvilinear Coordinates with Mesh Refinement Interfaces by a Fourth Order Finite Difference Method, SIAM J. Sci. Comp.  43(2) pp. A1472-A1496. doi:10.1137/20M1339702
 
+User's Guide
+------------
+Petersson, N.A.; Sjögreen, B.; Tang, H. (2023), User's Guide to SW4, version 3.0, LLNL-SM-741439 (LLNL-SM-741439)
 
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