source: sans/Analysis/trunk/Put in User Procedures/SANS_Models_v3.00/HardSphereStruct.ipf @ 42

#pragma rtGlobals=1             // Use modern global access method.

////////////////////////////////////////////////
// GaussUtils.ipf is not required (no smearing calculation done) PlotUtils.ipf should be included
////////////////////////////////////////////////
// this function is for the hard sphere structure factor
//
//
// 06 NOV 98 SRK
////////////////////////////////////////////////

Proc PlotHardSphereStruct(num,qmin,qmax)
        Variable num=128,qmin=0.001,qmax=0.3
        Prompt num "Enter number of data points for model: "
        Prompt qmin "Enter minimum q-value (^-1) for model: "
        Prompt qmax "Enter maximum q-value (^-1) for model: "
        
        Make/O/D/n=(num) xwave_hss,ywave_hss
        //xwave_hss = (x+1)*((qmax-qmin)/num)
        xwave_hss = alog(log(qmin) + x*((log(qmax)-log(qmin))/num))     
        Make/O/D coef_hss = {50,0.2}
        make/o/t parameters_hss = {"Radius (A)","vol fraction"}
        Edit parameters_hss,coef_hss
        ywave_hss := HardSphereStruct(coef_hss,xwave_hss)
        Display ywave_hss vs xwave_hss
        ModifyGraph marker=29,msize=2,mode=4
        Label bottom "q (\\S-1\\M)"
        Label left "Structure Factor"
        AutoPositionWindow/M=1/R=$(WinName(0,1)) $WinName(0,2)
End

///////////////////////////////////////////////////////////
// no smeared version is calculated - it is simply not appropriate

///////////////////////////////////////////////////////////////
// unsmeared model calculation
///////////////////////////
Function HardSphereStruct(w,x) : FitFunc
        Wave w
        Variable x
                        
//     SUBROUTINE HSSTRCT: CALCULATES THE STRUCTURE FACTOR FOR A
//                         DISPERSION OF MONODISPERSE HARD SPHERES
//                         IN THE PERCUS-YEVICK APPROXIMATION
//
//     REFS:  PERCUS,YEVICK PHYS. REV. 110 1 (1958)
//            THIELE J. CHEM PHYS. 39 474 (1968)
//            WERTHEIM  PHYS. REV. LETT. 47 1462 (1981)
//
// Input variables are:
        //[0] radius
        //[1] volume fraction
        //Variable timer=StartMSTimer
        
        Variable r,phi,struc
        r = w[0]
        phi = w[1]

// Local variables
        Variable denom,dnum,alpha,beta,gamm,q,a,asq,ath,afor,rca,rsa
        Variable calp,cbeta,cgam,prefac,c,vstruc
//  COMPUTE CONSTANTS
//
      DENOM = (1.0-PHI)^4
      DNUM = (1.0 + 2.0*PHI)^2
      ALPHA = DNUM/DENOM
      BETA = -6.0*PHI*((1.0 + PHI/2.0)^2)/DENOM
      GAMM = 0.50*PHI*DNUM/DENOM
//
//  CALCULATE THE STRUCTURE FACTOR
//     
// loop over q-values used to be here
//      DO 10 I=1,NPTSM
        Q = x           // q-value for the calculation is passed in as variable x
        A = 2.0*Q*R
//        IF(A.LT.1.0D-10)  A = 1.0D-10
        ASQ = A*A
        ATH = ASQ*A
        AFOR = ATH*A
        RCA = COS(A)
        RSA = SIN(A)
        CALP = ALPHA*(RSA/ASQ - RCA/A)
        CBETA = BETA*(2.0*RSA/ASQ - (ASQ - 2.0)*RCA/ATH - 2.0/ATH)
        CGAM = GAMM*(-RCA/A + (4.0/A)*((3.0*ASQ - 6.0)*RCA/AFOR + (ASQ - 6.0)*RSA/ATH + 6.0/AFOR))
        PREFAC = -24.0*PHI/A
        C = PREFAC*(CALP + CBETA + CGAM)
        VSTRUC = 1.0/(1.0-C)
        STRUC = VSTRUC
//   10 CONTINUE
        //Variable elapse=StopMSTimer(timer)
      //Print "HS struct eval time (s) = ",elapse
      RETURN Struc
End
// End of HardSphereStruct