## saxsdata.ini_saxs() — Initialization of SAXS data

`ini_saxs(atmsel, filename='$(LIB)/formfactors-int_tab_solvation.lib', s_min=0.0, s_max=2.0, maxs=100, nmesh=100, natomtyp=15, represtyp='heav', wswitch='uniform', s_hybrid=0.0, s_low=0.0, s_hi=2.0, spaceflag='real', rho_solv=0.334, use_lookup=True, nr=5000, dr=0.1, nr_exp=300, dr_exp=1.0, use_offset=False, use_rolloff=False, use_conv=False, mixflag=False, pr_smooth=False)`

> Routine to initialize the SAXSDATA structure. Here the sampling in reciprocal space needs to be specified; currently only equidistant sampling is possible. Moreover, the parameters for the scoring function and for its computation are set.

> s_min and s_max specify the minimum and maximum frequency in reciprocal space, in Å. maxs gives the maximum number of frequencies, and nmesh the actual number (which must be less than maxs).

> natomtyp gives the number of ”atoms”, i.e. scattering centers. represtyp specifies the representation : 'heav', 'allh', or 'CA'. filename is the name of the library for formfactors. wswitch is the character for filter of scoring function: 'unity', 'sq', or 'hybrid'. If 'hybrid', then s_hybrid is the frequency above which weighting is applied. s_low and s_hi give the lower and upper cutoff for the bandpass filter in Å. spaceflag specifies how should be computed. 'real' space via or 'reciprocal'. 'real' is more than a magnitude faster but less accurate for high resolution ().

> rho_solv gives the electron density of solvent, in Å. (The default 0.334 corresponds to HO.) use_lookup, if `True`, uses lookup tables for SINC and COS functions, giving a significant increase in speed for 'reciprocal' mode.

> nr gives the number of points for sampling, and dr the spacing of these points in Å. nr_exp gives the number of points for sampling, and dr_exp their spacing.

> If use_offset is `True` then allowance is made for an additive constant in the experimental spectrum. If use_rolloff is `True`, allowance is made for Gaussian rolloff in the model spectrum. If use_conv is `True`, the spectrum is multiplied with the formfactor of nitrogen ( 3Å) spectrum. If mixflag is `True` then more than one conformation is modeled simultaneously. If pr_smooth is `True` smoothing of p(r) is done.