# Differences

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 del_parameter [2015/08/14 09:30]johnsoevans created del_parameter [2020/07/16 11:29] (current) 2019/07/26 17:14 johnsoevans 2019/07/26 17:13 johnsoevans 2015/08/14 10:14 johnsoevans 2015/08/14 10:13 johnsoevans 2015/08/14 09:47 johnsoevans 2015/08/14 09:43 johnsoevans 2015/08/14 09:35 johnsoevans 2015/08/14 09:30 johnsoevans created Next revision Previous revision 2019/07/26 17:14 johnsoevans 2019/07/26 17:13 johnsoevans 2015/08/14 10:14 johnsoevans 2015/08/14 10:13 johnsoevans 2015/08/14 09:47 johnsoevans 2015/08/14 09:43 johnsoevans 2015/08/14 09:35 johnsoevans 2015/08/14 09:30 johnsoevans created Line 4: Line 4: For user defined parameters del defaults to 1e-5 which may be too small for some parameters. An optimum value of del is one that traverses the minimum in around 5 steps, with each step increasing by 1.6. Thus a search is performed as follows: For user defined parameters del defaults to 1e-5 which may be too small for some parameters. An optimum value of del is one that traverses the minimum in around 5 steps, with each step increasing by 1.6. Thus a search is performed as follows: - Let s = x + ​Let s = x - First point evaluated at P(x) + First point evaluated at P(x) - s = s + 1.6 del + s = s + 1.6 del - Next point evaluated at P(x+s) + Next point evaluated at P(x+s) - Do + + ​Do s = s + 1.6 del s = s + 1.6 del If P is decreasing then If P is decreasing then Line 15: Line 16: evaluate at P(x-s) evaluate at P(x-s) endif endif - Loop + Loop + + Some built in values are: + + - The loop is performed ​5 times. + cell parameter ​      %min = Max(1.5, 0.995 Val - .05);  %max = 1.005 Val + .05;         del = 0.0001 Val; + cell angle           %min = Max(1.5, Val - .2);         %max = Val + .2;                del 0.01 + scale                 min 1e-15                                                         del = Abs(Val) 0.003 + 1e-10; + fractional_coordinate min = Val-Constant(1/​Get(a)); ​     max = Val+Constant(1/​Get(a)); ​ del = Constant(.1 / Get(a)); + sh_Cij_prm ​           min = -Abs(Val) 2 - .1;            max =  Abs(Val) 2 + .1;        del = If(Val < 0, -0.01, .01) + .01 Val; + ​ + ​