<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:16px"><div id="yui_3_16_0_1_1424641640274_46433" dir="ltr">Hi, <br></div><div id="yui_3_16_0_1_1424641640274_46455" dir="ltr"><br></div><div id="yui_3_16_0_1_1424641640274_46457" dir="ltr"> Contingency analysis of power systems requires to solve a sequence <br></div><div id="yui_3_16_0_1_1424641640274_46490" dir="ltr">a (non-)linear systems in which the Jacobian/matrix changes by a <br></div><div id="yui_3_16_0_1_1424641640274_46502" dir="ltr">rank-2/rank-1 update. <br></div><div dir="ltr"><br></div><div id="yui_3_16_0_1_1424641640274_46504" dir="ltr"> Does the PETSc interface to GAMG allow to freeze the AMG hierarchy <br></div><div dir="ltr">for a given matrix (base case) and to reuse this hierarchy in solving a list of <br></div><div dir="ltr">slightly perturbed linear problems (list of contingencies)? <br></div><div id="yui_3_16_0_1_1424641640274_46583" dir="ltr"><br></div><div id="yui_3_16_0_1_1424641640274_46577" dir="ltr"> Thanks, Domenico. <br></div><div id="yui_3_16_0_1_1424641640274_46119" style="font-family: times new roman, new york, times, serif; font-size: 16px;"><div id="yui_3_16_0_1_1424641640274_46118" style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> </div> </div> </div></body></html>