檢視 $diffusortype 的原始碼

$diffusortype is a special function to define the material parameters. Some materials are diffusive material so that we can apply the diffusor parameters. 

The usage is 

 $diffusortype
 type_1 diffusion_length_1
 type_2 diffusion_length_2
 ...
 ...  totalregions
 ...
 type_Nth diffusion_length_N

In side the diffusor, the program will decide if it will change location depending on diffusion length. 

 Type 1,  random diffusion
 Type 2,  cos dependent
 Type 3,  cos^2 dependent


        elseif(diffusortypess==1) then

            I=(1-exp(-1.0*compare(3)*diffusorlength))
            call random_number(diffusing)
            if(diffusing<I)then
              x=cx
              y=cy
              intersectionss=2
              call random_number(angle)
              vx=cos(angle*2*pi)
              vy=sin(angle*2*pi)
            end if
        elseif(diffusortypess==2) then
            I=(1-exp(-1.0*compare(3)*diffusorlength))
            call random_number(diffusing)
            if(diffusing<I)then
               x=cx
               y=cy
               intersectionss=2
               call random_number(angle)
               theta = (1-cos(angle*pi/2) )*pi/2
               call random_number(angle)
               if(angle .ne.0.5) then
                  theta= theta*(angle-0.5)/abs(angle-0.5)
               end if
               oldvx=vx
               oldvy=vy
               if(oldvy>0) then
                 oldtheta=acos(oldvx/sqrt(oldvx*oldvx+oldvy*oldvy))
               elseif(oldvy==0.0) then
                  if(oldvx >0.0) oldtheta=0.0
                  if(oldvx <0.0) oldtheta=pi
               else
                 oldtheta=2*pi-acos(oldvx/sqrt(oldvx*oldvx+oldvy*oldvy))
               end if

               vx=cos(theta+oldtheta)
               vy=sin(theta+oldtheta)
            end if
        elseif(diffusortypess==3) then
            I=(1-exp(-1.0*compare(3)*diffusorlength))
            call random_number(diffusing)
            if(diffusing<I)then
               x=cx
               y=cy
               intersectionss=2
               call random_number(angle)
               theta = (1-cos(angle*pi/2) )**2*pi/2
               call random_number(angle)
               if(angle .ne.0.5) then
                  theta= theta*(angle-0.5)/abs(angle-0.5)
               end if
               oldvx=vx
               oldvy=vy
               if(oldvy>0) then
                 oldtheta=acos(oldvx/sqrt(oldvx*oldvx+oldvy*oldvy))
               elseif(oldvy==0.0) then
                  if(oldvx >0.0) oldtheta=0.0
                  if(oldvx <0.0) oldtheta=pi
               else
                 oldtheta=2*pi-acos(oldvx/sqrt(oldvx*oldvx+oldvy*oldvy))
               end if

               vx=cos(theta+oldtheta)
               vy=sin(theta+oldtheta)

            end if

        end if