for #1961 added Derbenev-Skrinsky force formula
for #1961 added Derbenev-Skrinsky force formula

mrakitin/sirepo,mkeilman/sirepo,radiasoft/sirepo,mrakitin/sirepo,mrakitin/sirepo,radiasoft/sirepo,mrakitin/sirepo,mkeilman/sirepo,radiasoft/sirepo,mkeilman/sirepo,radiasoft/sirepo,mkeilman/sirepo,radiasoft/sirepo