id,summary,reporter,owner,description,type,status,priority,milestone,component,resolution,keywords,cc,workpackage
805,improve accuracy of fcc/bcc/sc,pkienzle,,"fcc/bcc/sc paracrystal models use the following expression:
{{{
exp_qd = mp.exp(-qd**2*a/2)
return (1 - exp_qd**2) / (1 - 2*exp_qd*mp.cos(qd*b) + exp_qd**2)
}}}
this can behave poorly for low q, even though the limit exists:
{{{
lim x->0 [(1 - exp(-a x^2)) / (1 - 2*exp(-a x^2/2) cos(b x) + exp(-a x^2)]
=> a/b^2
}}}
Maybe replace this with a Taylor expansion at low q so that the model can run in single precision.
Note that there are alternate forms of this expression:
{{{
sinh(ax^2) / (cosh(ax^2) - cos(bx))
tanh(ax^2) / (1 - cos(bx)/cosh(ax^2)
}}}",defect,new,major,SasView 4.3.0,SasView,,,,SasView Bug Fixing